Cargo Work Draft, Trim and Stability The Load Line Marks
LR – the symbols of the classification society (Lloyds Register) by the side of the Plimsoll mark TF – Tropical Fresh (water)
F – Fresh Water
S – Summer (Sea Water)
W – Winter (Sea Water)
WNA – Winter North Atlantic (Sea Water)
T – Tropical (Sea Water)
Criteria of Stability: Extract from the Load Line Rule (1968) The area under the curve of Righting Levers shall not be less than: 0.055 metre-radians up to an angle of heel of 30˚ 0.09 metre-radians up to an angle of heel of 40˚ 0.03 metre-radians between the angles of heel of 30˚ and 40˚ The Righting Lever shall be at least 0.20 metre at an angle of heel equal to or greater than 30˚ The maximum Righting Lever shall occur at an angle of heel not less than 30˚ The Initial Transverse Metacentric Height (GM) shall not be less than 0.15 metre
Ship Stability – working with ‘kg’, TM, Draft, Displacement and Trim including LCB and LCF Method of working:
The following example shows how a ships stability booklet has pre-determined conditions of loading and the consequent stability criteria. The said condition is 12; each ‘Departure’ condition has an ‘Arrival’ condition. In the Departure condition the vessel is assumed to be sailing out with a load of cargo and with full bunkers and stores. The ballast is negligible. In the Arrival condition the vessel is assumed to have arrived her disport/ way port (may be bunkering for long voyage), here the cargo remains the same only change is in the bunkers and FW. The Arrival condition is to be worked out prior departure since the arrival condition determines the loading of the cargo. Since no vessel would like to arrive a port in a critical condition – not satisfying the stability criteria. The weight is multiplied with the ‘kg’ of each compartment to obtain the vertical moments. These are added up (all – cargo, ballast, Bunkers and light ship) and the total of the V-M is divided by the displacement to get the final KG In the same way the weight is multiplied with the ‘lcg’ of each compartment to obtain the longitudinal moments. These are added up (all – cargo, ballast, Bunkers and light ship) and the total of the L-M is divided by the displacement to get the final LCG. Noting the Displacement the tables are referred to obtain the LCB, Mean Draft and the Trimming Moment. With these inputs the final drafts and the GM is calculated. For obtaining the Fluid GM, the FSM of the compartments are read off from the tank data sheets. The total of the FSM when divided by the displacement gives the FSC that is to be subtracted from the GM to obtain the GM (F). The following shows the departure condition of a ship, the general particulars are given.
And the following gives the arrival condition for the same ship – the cargo is the same, only change being the fuel and the ballast.
The following are extract from the hydrostatic table of ship ‘A’.
Given that the morning draft in sea water of ship ‘A’ is Forward: 8.92m and Aft: 9.12m Ship ‘A’ loads cargo throughout the morning shift and her sailing drafts are: Fwd: 8.99m, Aft: 9.19m To find the amount of cargo loaded. Note, during the morning the ship received H.O. bunkers – 100MT and consumed 10MT of FW. Morning Mean Draft: (8.92 + 9.12)/ 2 = 9.02m Sailing Mean Draft: (8.99 + 9.19)/ 2 = 9.09m
Displacement at 9.02m: 20419 Displacement at 9.09m: 20604 Thus the difference in displacement would be: (20604 – 20419) = 185 MT Bunkers received: 100MT FW consumed: 10MT Thus the cargo loaded would be: 185 – 100 = 85 MT (correcting for the bunker) and 85 + 10 = 95MT (correcting for the FW consumed) For change of trim the earlier example is to be referred.
C Caarrggoo W Woorrkk Securing Cargo
Need for solid stow and securing of all cargoes
Cargo onboard a ship will tend to shift with the motion of the ship. This necessitates the cargo to be lashed (secured) to the ship structure. However the lashing with ropes/ wire ropes/ iron restraining bars is not very effective because of the fact that the tightened lashings have a tendency to work loose with the motion of the ship.
On shore any nut which is fitted tightly on a bolt works loose with vibrations as such - spring washers are used together with check nuts and split pins to prevent the working loose of such nuts. This is not practical on shipboard lashings - except for turnbuckles and bottle screws with restraint bars. Below deck lashings further are not attended to during sailing and if they work loose it is practically impossible to do a very effective job to re-secure them. Temporary measures are often adopted and these may not be very effective as stated earlier. Thus the only way to prevent the lashings from working loose is to stow the cargo very close to each other and then to shore the cargo with timber. This would prevent the cargo from acquiring momentum while swaying with the ship and thus prevent to a large extent the working loose of the lashings.
For bagged cargo if the same is not stowed solidly and thus allowing too much of broken stowage, would tend to shift with the motion of the ship, thus shifting the centre of gravity laterally and inducing a list to the ship. This coupled with the heeling of the ship would make the weather deck of a ship too close to the water line and thus endanger the safety of the ship. Bulk cargo on general cargo carriers are therefore saucered with the same cargo, in order to prevent the cargo from shifting to one side. Deck cargo due to the high KG is especially vulnerable lateral shifting and the lashings work loose and also to part lashing. Especially since the transverse momentum gained by such cargo during the rolling of a ship is liable to part lashings. Thus all deck cargo has to be definitely shored and then also lashed to deny the cargo from gaining any momentum.
Deck cargo - Lashed
Deck Cargo - Shored and Lashed
Cargo liable to slide during rolling, such as steel rails, should be Stowed fore and aft All long cargoes such as steel rails, pipes, long steel plates as well as steel coils are stowed with their ends in the fore and aft direction. This again is necessary due to the fact that most of theses cargo cannot be individually lashed they rather grouped into bundles and the bundles are lashed to make many small bundles of pipes or rails as the case may be. This prevents the individual pipes from sliding and since as mentioned the transverse momentum is quite large when the ship is rolling, and the pipes are thus prevented from damaging the sidewalls of the hold. This is severe since repeated banging has resulted in tearing holes in the shipside plates below the waterline and the ship capsizing due the inflow of water. If the pipes / rails are stowed in the fore and aft direction this is prevented.
Bundling of long cargo (pipes/ rails):
This is the first tier. It is important to place the dunnage to spread the load as well as to facilitate the passing of slings at the disport. The lashing wires are also placed prior to loading the cargo. The size of the bundles should be to the capacity of the derrick/ crane that would be used to discharge the cargo. The number of lashing wires is dependent on the weight of the bundles as well as the length of the cargo.
As each bundle is completed the lashings are closed and tightened. And subsequently dunnage is again placed and the lashing wires again spread on top of the earlier cargo.
Stowage and securing for vehicles and trailers Vehicle lashing on deck Force parallel to and across the deck = 1.0 W Force normal to the deck = 1.4 W Force in the longitudinal direction = 0.3 W The above forces are intended to represent the total force to be applied in each direction i.e., the aggregate of the static and the dynamic forces. Case 1 – Vehicle stowed in Fore and Aft direction: The forces preventing tipping of the vehicle are the vertical downward force and the lashings holding the vehicle (FLT) Taking moments about A (the outer edge of wheel i.e., fulcrum position) FLT x L = (1.0 W x 2/3 H) – (1.4 W – X) FLT x (X + Y) sin = W (0.67 H – 1.4 X) FLT = (W (0.67 H – 1.4 X) / ((X + Y) sin) Note the importance of the fulcrum position (A), The height of the centre of gravity, normally taken as 2/3 H is the angle of inclination of the lashings To examine the force causing the vehicle to slide sideways: For this example a trailer is supported by wheels on the one end and with a trestle at the other end.
In both cases sliding is resisted by the frictional resistance ‘’ between the tyre/ deck and the trestle/ trailer frame and also lashings (FLS). Case 1 – Effect at the trestle end of trailer. Note: Assuming ½ total forces act at each end of trailer then effective sliding force = 0.5 W – 0.7 W x Ls (assume 0.2) = 0.5 W – 0.14 W = 0.36 W then the force in the lashing resisting sliding = FLS = 0.36 W / cos
Case 2 – Effect at wheel end of trailer. Effective sliding force = 0.5 W – 0.7 W x (assume 0.4) = 0.5 W – 0.28 W = 0.22 W then the force in the lashing resisting sliding = FLS = 0.22 W / cos Note the importance of ‘’ the coefficient of friction and the angle of inclination of the lashings. In the above it can be seen near vertical lashing is great to prevent tipping but is useless for sliding whereas a near horizontal is great for sliding but is useless for tipping. So a correct angle of inclination should be fixed appropriate for the cargo. In general the safe working load (S.W.L.) of lashing wires is taken as 1/3 the Breaking load. If chain is used for lashing then: If made of H.T. steel then the SWL would be 40% of the Breaking load. And if made of ordinary steel then the SWL would be 33% of the Breaking load. Efficient securing of cargoes is essential for the safety of the ship as well as the cargo Securing of cargo is of prime importance not only for the cargoes themselves but also for the ship as a whole including the crew that sail on her. Improperly secured cargo will shift in a seaway and can endanger the cargo as well as the ship. In the worst cases the cargo may fall overboard and may endanger other ships such cargoes like logs and containers have been noted to have floated and come within the sea-lanes. When a container falls overboard it must be remembered that it does so in spite of it being secured on the ship as well as the opposition to this being offered by the ship structure. Thus when it does go overboard it does after causing a great amount of structural damage. There are many instances of cargo improperly secured breaking the lashings and punching a hole at or below the waterline and the ship having been lost with casualties.
Deck cargos if they part their lashings are liable to cause extensive damage, which can endanger the watertight integrity. Even minor movement of heavy cargoes has been known to shear off air pipes and sounding pipes resulting in water entering the tanks or other spaces below deck. Fire lines have also been damaged due to inadvertent movement of cargo. Accommodation ladders as well as companionway can be damaged due to the cargo movement on deck in a seaway. Even if the ship is not lost the damage such heavy cargoes can bring upon the structure of the ship is very heavy. Crew has often been sent to re-secure such cargo in rough weather with the crew suffering loss of limbs and other injuries. Stowage and securing of deck cargo should be adequate for the worst conditions which could be experienced Good stowage and good securing arrangement should be foreseen prior loading the cargo. If it is required extra lugs and eyes on deck have to be welded to provide lashing points for the cargo- this is generally done for heavy lifts or cargoes of odd sizes.
Securing should be always for the worst weather that would be encountered. Many a ship have suffered damage to cargoes and to their own structure by neglecting good and adequate lashing while on a short voyage, failing to take into account diversions and anchorage at open roadstead and cyclonic weather. Hatches should be securely closed and cleated before loading over them Once the cargo below deck has been loaded and all securing has been completed (securing can continue after the hatches are secured provided there is adequate space for the crew to enter and to lash), the hatches are closed and battened down and all cleats and centre wedges should be in place. Only after the above have been completed should any cargo be loaded on to the hatch tops. If this is not done, and the hatch is battened down after the cargo has been loaded on to the hatch tops the battening down and the fitting of the cleats as well as the centre wedges
would be ineffective since the weight of the cargo would not permit the hatch covers to be correctly in place and the hatch would leak in a seaway or even in rain.
Deck Cargo
Cargo which are normally carried on deck include the following but are not limited to these and many exceptional cargoes may be carried and also have been carried in the past. Dangerous cargo – IMDG cargo not permitted on deck Large packages which due to any size restriction may have to be loaded on to the deck The above includes engineering or construction equipment Odd size package Where the bulk volume far exceeds the weight of the cargo – knocked down bridges, port equipment – not easily liable to weather damage. Occasionally livestock in limited numbers Onions or other perishables – short voyages with the weather holding Yachts – luxury boats. Cast iron goods – man hole covers – pipes. The list is endless and it all depends on the routes, the trading pattern and the weather. The cargo whether on deck or under deck stow has to be stowed well and the cargo should be prevented from moving and gaining enough momentum to part lashings and damage the ship structure. Deck cargo is liable to damage itself – fall overboard and thus be lost. However the misery does not stop here in the act of parting lashing and going overboard the deck cargo unleashes considerable damage to the ship structure as well as the crewmembers. Small apparently insignificant items such as sounding pipes and air pipes are often torn out and this may endanger the ship from the resulting chances of flooding lower down compartments.
Crewmembers ordered to lash cargo where the lashings have parted have been seriously injured and some have lost lives combating the shifting cargo. The point is to have a good solid stow – prevent the cargo from shifting and gaining momentum with the shift. Since this would part any strong lashing. The lashing undertaken should be for the worst sea condition that may be experienced. Deck cargo loading on top of hatch covers should be carefully planned. All loading of under deck spaces should have been completed – lashing may continue with portable lights. The hatch covers should be closed and battened down – all side wedges as well as cross wedges (centre wedges) should have been fitted. With the hatch cover sealed for sea, the space should then be given out for loading of deck cargo. The permissible load density of the hatch covers should be checked and timbers laid to spread the weight of the cargo. The load density of the hatch covers are given for a new vessel and as the ship ages the load density would reduce due to fatigue of the metal as well as wear and tear. Thus the utmost need to spread the weight using timber. Shoring and toming of the hatch cover from below deck is practically useless since the hatch cover moves/ slides somewhat with the motion of the ship. The height of the cargo on the hatch covers as well as that on deck should not be so high that the view is obstructed from the Navigating Bridge.
Ice accumulation on hatch cover and on deck
The above photographs show the extent of the weight that Ice accumulation can pose for a ship. The weight on deck may eventually lead a ship to progress to a condition of ‘angle of loll’. The weight of the ice may be in excess of a hundred tonnes, and thus the danger of a ship regarding stability. As with the above any deck cargo for that matter would have a very high KG as such the GM (F) would be quite small. Especially in the case of GC vessels, which do not have a very large GM (F) the loading of deck cargo, is bound to lead to further loss of GM (F). If the ship loads the deck cargo with her own gear then the ship would during the loading operation have still further low GM (F) due to the KG of the load being at the top of the derrick/ crane for part of the loading sequence. Containers on deck
Containers when they are loaded on deck are subject to the following consideration – barring stability, which would have been planned for. The load density of the deck Spreading the load of the container evenly Chocking the container base to prevent shifting due to rolling or pitching Lashing the container for the above as well to prevent the container from being bodily lifted.
Placing the containers in as close a group as possible Safeguarding the sounding pipes and the air pipes within the periphery of the container space. Keeping the fire hose boxes clear as well as the passage leading to them, the fire hydrants should similarly be kept clear. No lashing should be taken which would damage or cause to be damaged the fire lines. Checking that the leads for the lashing wires are adequate as well as that the chocking points are well supported Keeping a passage for crew members to check the lashings during g voyage. In general the close stow is difficult on GC vessels where the container is usually loaded between the hatch coaming and the bulwark. So the container should be loaded as close as possible to the hatch coaming, as well as close to the Mast House structure. If few containers are being loaded then the shelter offered by the Mast House structure should be kept in mind. The load is spread by having the container loaded onto timbers at least 4” x 4”. The timbers should be extended to well beyond the shoe of the container in all directions to spread the load. Once this is done the chocking of the container is started. Again heavy timbers are used and the container is first secured to prevent any lateral and transverse shifting. While selecting chocking points all heavy framework should be selected. Bulwark stays are not strengthened enough to be used as chocking points. Hatch coamings may be used and as a last resort bulwark stays. After the chocking is completed the container is lashed. The lashing is further to prevent the longitudinal as well as the transverse shifting. For this the base shoes offer the best lashing points. To prevent the container being bodily shifted out the lashings are continued to the top shoes. All lashing should be separate in the sense that a single lashing wire should not be passed over a few shoes and then lashed at the final point. Each lashing should have a turnbuckle or bottle screw incorporated and there should be at least 60% free thread in them after completion of lashing.
The bottom lashing and the top lashing should not be counted together fore the purpose of assessing the total number of lashings taken for the container. The top lashings are for bodily rise and as such should be counted separately. As a thumb rule, if the SWL of the lashing wire is 2T then to lash the top of a 20T container the number of lashings should be a minimum of 10 (all well positioned), similarly the bottom should have 10. The bottom lashings may be reduced depending upon the chocking of the container and the availability of the lashing point. Note that a single strong point for lashing should not have more than 2 lashing wires – the preferred would be 1, however it is often impossible to find so many lashing points.
This shows a container ship lashing; note that the container is loaded onto the ship shoe slots which are strengthened, the rod lashings are only for the top of the containers. Here the bottom shoes are not lashed since the ships sunken shoes and twist locks effectively chock and lash the bottom of the container.
Stowage and Lashing of Timber deck cargoes as laid down by IMO code of Safe Practice for Ships Carrying Timber Deck Cargoes Purpose The purpose of the Code is to make recommendations on stowage, securing and other operational safety measures designed to ensure the safe transport of mainly timber deck cargoes. Application This Code applies to all ships of 24 m or more in length engaged in the carriage of timber deck cargoes. Ships that are provided with and making use of their timber load line should also comply with the requirements of the applicable regulations of the Load Line Convention. Timber means sawn wood or lumber, cants, logs, poles, pulpwood and all other type of timber in loose or packaged forms. The term does not include wood pulp or similar cargo. Timber deck cargo means a cargo of timber carried on an uncovered part of a freeboard or superstructure deck. The term does not include wood pulp or similar cargo. Timber load line means a special load line assigned to ships complying with certain conditions related to their construction set out in the International Convention on Load Lines and used when the cargo complies with the stowage and securing conditions of this Code. Weather deck means the uppermost complete deck exposed to weather and sea. The stability of the ship at all times, including during the process of loading and unloading timber deck cargo, should be positive and to a standard acceptable to the Administration. It should be calculated having regard to: The increased weight of the timber deck cargo due to: Absorption of water in dried or seasoned timber, and Ice accretion, if applicable; Variations in consumables; The free surface effect of liquid in tanks; and Weight of water trapped in broken spaces within the timber deck cargo and especially logs.
Safety precautions to be taken as far as stability of the ship is concerned The master should: Cease all loading operations if a list develops for which there is no satisfactory explanation and it would be imprudent to continue loading; Before proceeding to sea, ensure that: The ship is upright; The ship has an adequate metacentric height; and The ship meets the required stability criteria. Ships carrying timber deck cargoes should operate, as far as possible, with a safe margin of stability and with a metacentric height which is consistent with safety requirements but such metacentric height should not be allowed to fall below the recommended minimum. However, excessive initial stability should be avoided as it will result in rapid and violent motion in heavy seas which will impose large sliding and racking forces on the cargo causing high stresses on the lashings. Operational experience indicates that metacentric height should preferably not exceed 3% of the breadth in order to prevent excessive accelerations in rolling provided that the relevant stability criteria are satisfied. This recommendation may not apply to all ships and the master should take into consideration the stability information obtained from the ship’s stability manual.
STOWAGE
General Before timber deck cargo is loaded on any area of the weather deck: Hatch covers and other openings to spaces below that area should be securely closed and battened down; Air pipes and ventilators should be efficiently protected and check valves or similar devices should be examined to ascertain their effectiveness against the entry of water; Accumulations of ice and snow on such area should be removed; and It is normally preferable to have all deck lashings, uprights, etc., in position before loading on that specific area. This will be necessary should a preloading examination of securing equipment be required in the loading port. The timber deck cargo should be so stowed that: Safe and satisfactory access to the crew’s quarters, pilot boarding access, machinery spaces and all other areas regularly used in the necessary working of the ship is provided at all times; Where relevant, openings that give access to the areas can be properly closed and secured against the entry of water; Safety equipment, devices for remote operation of valves and sounding pipes are left accessible; and It is compact and will not interfere in any way with the navigation and necessary working of the ship. During loading, the timber deck cargo should be kept free of any accumulations of ice and snow. Upon completion of loading, and before sailing, a thorough inspection of the ship should be carried out. Soundings should also be taken to verify that no structural damage has occurred causing an ingress of water. On ships provided with, and making use of, their timber load line, the timber deck cargo should be stowed so as to extend:
.1 over the entire available length of the well or wells between superstructures and as close as practicable to end bulkheads; .2 at least to the after end of the aftermost hatchway in the case where there is no limiting superstructure at the aft end; .3 athwartships as close as possible to the ship sides, after making due allowance for obstructions such as guard rails, bulwark stays, uprights, pilot boarding access, etc., provided any area of broken stowage thus created at the side of the ship does not exceed a mean of 4% of the breadth; and .4 to at least the standard height of a superstructure other than a raised quarterdeck. The basic principle for the safe carriage of any timber deck cargo is a solid stowage during all stages of the deck loading. This can only be achieved by constant supervision by shipboard personnel during the loading process. SECURING General Every lashing should pass over the timber deck cargo and be shackled to eye plates and adequate for the intended purpose and efficiently attached to the deck stringer plate or other strengthened points. They should be installed in such a manner as to be, as far as practicable, in contact with the timber deck cargo throughout its full height. All lashings and components used for securing should: .1 possess a breaking strength of not less than 133 kN; .2 after initial stressing, show an elongation of not more than 5% at 80% of their breaking strength; and .3 show no permanent deformation after having been subjected to a proof load of not less than 40% of their original breaking strength. Every lashing should be provided with a tightening device or system so placed that it can safely and efficiently operate when required. The load to be produced by the tightening device or system should not be less than: .1 27 kN in the horizontal part; and
.2 16 kN in the vertical part. NOTE: 1 Newton equals 0.225 lbs. force or 0.1 kgf. Upon completion and after the initial securing, the tightening device or system should be left with not less than half the threaded length of screw or of tightening capacity available for future use. Every lashing should be provided with a device or an installation to permit the length of the lashing to be adjusted. The spacing of the lashings should be such that the two lashings at each end of each length of continuous deck stow are positioned as close as practicable to the extreme end of the timber deck cargo. If wire rope clips are used to make a joint in a wire lashing, the following conditions should be observed to avoid a significant reduction in strength: .1 the number and size of rope clips utilized should be in proportion to the diameter of the wire rope and should not be less than four, each spaced at intervals of not less than 15 cm; .2 the saddle portion of the clip should be applied to the live load segment and the U-bolt to the dead or shortened end segment; .3 rope clips should be initially tightened so that they visibly penetrate into the wire rope and subsequently be retightened after the lashing has been stressed. Greasing the threads of grips, clips, shackles and turnbuckles increases their holding capacity and prevents corrosion.
Uprights Uprights should be fitted when required by the nature, height or character of the timber deck cargo. When uprights are fitted, they should: .1 be made of steel or other suitable material of adequate strength, taking into account the breadth of the deck cargo; .2 be spaced at intervals not exceeding 3 m; .3 be fixed to the deck by angles, metal sockets or equally sufficient means; and .4 if deemed necessary, be further secured by a metal bracket to a strengthened point, i.e., bulwark, hatch coaming. Loose or packaged sawn timber The timber deck cargo should be secured throughout its length by independent lashings. The maximum spacing of the lashings should be determined by the maximum height of the timber deck cargo in the vicinity of the lashings: .1 for a height of 4 m and below, the spacing should be 3 m; .2 for heights of above 4 m, the spacing should be 1.5 m. The packages stowed at the upper outboard edge of the stow should be secured by at least two lashings each. When the outboard stow of the timber deck cargo is in lengths of less than 3.6 m, the spacing of the lashings should be reduced as necessary or other suitable provisions made to suit the length of timber. Rounded angle pieces of suitable material and design should be used along the upper outboard edge of the stow to bear the stress and permit free reeving of the lashings. Logs, poles, cants or similar cargo The timber deck cargo should be secured throughout its length by independent lashings spaced not more than 3 m apart.
If the timber deck cargo is stowed over the hatches and higher, it should, in addition be further secured by: .1 a system of athwarthship lashings (hog lashings) joining each port and starboard pair of uprights near the top of the stow and at other appropriate levels as appropriate for the height of the stow; and .2 a lashing system to tighten the stow whereby a dual continuous wire rope (wiggle wire) is passed from side to side over the cargo and held continuously through a series of snatch blocks or other suitable device, held in place by foot wires. The dual continuous wire rope should be led to a winch or other tensioning device to facilitate further tightening. Testing, examination and certification
All lashings and components used for the securing of the timber deck cargo should be tested, marked and certified according to national regulations or an appropriate standard of an internationally recognized standards institute. Copies of the appropriate certificate should be kept on board. No treatments, which could hide defects or reduce mechanical properties or strength, should be applied after testing. A visual examination of lashings and components should be made at intervals not exceeding 12 months. A visual examination of all securing points on the ship, including those on the uprights, if fitted, should be performed before loading the timber deck cargo. Any damage should be satisfactorily repaired. Lashing plans
One or more lashing plans complying with the recommendations of this Code should be provided and maintained on board a ship carrying timber deck cargo. Personnel Protection And Safety Devices During the course of the voyage, if there is no convenient passage for the crew on or below the deck of the ship giving safe means of access from the accommodation to all parts used in the necessary working of the ship, guard lines or rails, not more than 330 mm apart
vertically, should be provided on each side of the deck cargo to a height of at least 1 m above the cargo. In addition, a lifeline, preferably wire rope, set up taut with a tightening device should be provided as near as practicable to the centreline of the ship. The stanchion supports to all guard rails or lifelines should be spaced so as to prevent undue sagging. Where the cargo is uneven, a safe walking surface of not less than 600 mm in width should be fitted over the cargo and effectively secured beneath, or adjacent to, the lifeline. Where uprights are not fitted, a walkway of substantial construction should be provided having an even walking surface and consisting of two fore and aft sets of guard lines or rails about 1 m apart, each having a minimum of three courses of guard lines or rails to a height of not less than 1 m above the walking surface. Such guard lines or rails should be supported by rigid stanchions spaced not more than 3 m apart and lines should be set up taut by tightening device. As an alternative a lifeline, preferably wire rope may be erected above the timber deck cargo such that a crewmember equipped with a fall protection system can hook onto and work about the timber deck cargo. The lifeline should be: .1 erected about 2 m above the timber deck cargo as near as practicable to the centreline of the ship; .2 stretched sufficiently taut with a tightening device to support a fallen crewmember without collapse or failure. Properly constructed ladders, steps or ramps fitted with guard lines or handrails should be provided from the top of the cargo to the deck, and in other cases where the cargo is stepped, in order to provide reasonable access.
Action To Be Taken During The Voyage Tightening of lashings It is of paramount importance that all lashings be carefully examined and tightened at the beginning of the voyage as the vibration and working of the ship will cause the cargo to settle and compact. They should be further examined at regular intervals during the voyage and tightened as necessary. Entries of all examinations and adjustments to lashings should be made in the ship’s logbook.
Container Cargo
Sea Containers were invented in the mid 1950s by Malcolm McLean, a North Carolina trucking owner who grew tired of wasting his trucking company’s time with trucks standing idle in line as ships were unloaded bit by bit by dockworkers. McLean developed sealed truck trailers and the concept of loading and unloading the trailer interiors only at the points of origin and destination. The first ship modified to accept these “containers” on deck, sailed with 58 of them from New York to Houston in April 1956. This was the start of McLean’s company, the Sea-Land Corporation. The Matson Line (Hawaii) put the first fully containerized ship into service in 1960. The International Standards Organization (ISO) first established container standards in 1961. The ISO standard is not prescriptive and instead simply stipulates tests that the containers must pass. Modern container ships have only one problem – when the ship arrives in port, the object is to unload the containers quickly to get them on to their final destination and to get the container ships back out to sea fully loaded heading for the next port. To accomplish this, container ships are equipped with steel skeletons called “cell guides”. A special lifting fixture is used with remote actuators, which engage the corner blocks on the top of the container.
A recent survey indicates that port crane operators can execute full crane cycles to remove and position containers at rates of between 30 and 60 boxes per hour. Containers come in two basic sizes – 20 Footer and 40 Footer and are commonly known as TEU (Twenty Equivalent Units) and FEU (Forty Equivalent Units). The external body of the container is made of corrugated sheet metal and is not capable of taking any load. The four corners have shoes and are strengthened to take in load.
The inside bottom has a wooden ceiling. There are weather-insulted vents provided to facilitate venting. The weights marked on the containers are TARE weight and LADEN weight. TARE weight is the weight of the empty container and is usually 2200KGS for a TEU, while the LADEN weight may be anything from 20000KGS to 32000KGS (strengthened steel construction). The container shoes fitted at the corners are hollow with 5 oval slots to facilitate the fitting of container fittings as well as for lifting the container – either by using conventional wire slings or by spreaders.
Since the containers are concentrated weights the loading of the same require special heavy dunnaging to spread the load evenly over the deck – if carried as deck cargo on conventional general cargo ships. However the carriage of containers are primarily on container ships or on ships, which have been built to take in general cargo as well as containers to a limited extent. Lashing of containers on purpose ships are supplied from reputed lashing makers and have been tested for the loads they are to lash. Various fittings are used and all of these are generally carried on board.
Base stacker
Twist Lock
Double Stacker
Corner Eye Pad
Side Stack Thrust
Bridge
Fitting
Twist Lock
Rod Lashing Bar
Spacer Stacker
A spacer stacker is used where there is a difference between adjacent containers as loaded in their heights, one being the 8ft and the other 8.5FT. On normal ships where these fittings may not be available wire ropes are used however the number of ropes to be used would be decided by the weight of the container. On GC ships with no provision for built in shoes only single height loads are carried. However on container ships the hold stacks may extend to 7 high and on hatch top/ deck to 5 high. The hold and the deck/ hatch top being strengthened. The lashings to be done are specified in the container-lashing manual supplied to the ship from the building yard. This is not to be reduced since the stresses have been calculated and the number of lashings incorporated. The containers are loaded onto a container ship in a specified manner. The ship is divided into BAYS or ROWS. Looking from the side the bays are marked from forward to aft. The containers are stacked in tiers and are in general called the stacks. This way ensures that any container can be located very easily – knowing the bay number and the row number isolates the location and the stack height give the exact position of the container. On container ships the containers are lowered onto slots inside the holds, the holds bottom is provided with sunken shoes, twist locks/ stackers are fitted onto these and the container is lowered onto them.
Cell Guides on Deck – Open hatch concept:
Some containers are designed to carry refrigerated cargo, these special containers have their own cooling plant in built on one end of the container, and all that is required for the ship to provide is a power point for the electricity. The containers come with their own recording device and card, the ships officers has to renew the card on the expiry of the same, and is to see that the cooling plant does not stop functioning, manuals are provided whereby ships staff can do some minor repairs to the plant.
Today a variety of cargo which previously was thought could only be loaded onto a general cargo ship, is transported on container ships. An example is a tank, thus small parcels of liquid is carried on container ships.
Lashing of containers is very important since a typical container ship has a low GM(F), consequently the ship rolls quite a bit and the stresses developed by the cargo swaying is liable to break the lashings and put the containers into the sea.
All lashings are to be done following the ships lashing manual. In general the following is a typical lashing system, others may also be accepted if permitted by the manual.
The planning of loading of a container ship is normally undertaken ashore, but the officer in charge of the watch should keep an eye on the loading to detect errors in stowage which may occur. A particular watch should be kept for containers with dangerous goods placards to see that their stowage satisfies segregation requirements as laid down in the IMDG code. Other things to watch for are that container marked for underdeck stowage do not end up on deck – this is serious since the container may be for second port by rotation, also the heavier containers are generally loaded underdeck to increase the GM. Thus in addition to a loss of GM the ship would also have a mess up at the disport. Refrigerated containers should be loaded where they can be connected to the ship’s power supply and the duty officer is to ensure the same. While loading a slight slackening of watch can become a liability since the gantries load very fast and to unload or to shift is expensive and time consuming – even if the fault actually is of the port. Sometimes containers are loaded which due to the nature of the contents have to be overstowed, in this case the container is loaded and the container is then blocked off so that there would be no chance of any pilferage – such containers may carry – currency/ coins, drugs, and mail or other high value cargo.
Bulk Cargo (Not Grain)
Bulk cargoes (other than grain) The officer of the watch should know the pre-planned loading procedure regarding quantities to be loaded in each space, the order of deballasting tanks and shifting the vessel under loading chutes. The procedure will have been worked out to keep stresses within acceptable limits and to finish with a satisfactory weight distribution and trim. The officer of the watch should see that the plan is followed, particularly at berths with only one loading chute, to avoid over-stressing the ship. Code of Safe Practice for Solid Bulk Cargoes BC Code is intended to set a standard for the safe stowage and carriage of solid bulk cargoes. This Code is a recommended guide for ship owners, shippers and masters and shall apply to all shipments of bulk cargoes.
The list of products appearing in the Appendices of the BC Code, however, is by no means exhaustive. Consequently, before any bulk cargo is loaded, it is essential to ascertain (normally from the shipper) the current physical and chemical properties of the cargo, as required under SOLAS Chapter VI. General requirements
Before and during loading, transport and unloading of bulk cargoes, all necessary safety precautions including any regulations or requirements should be observed, including the following: 1. Dangerous Bulk Material Regulations 2. Safe Working Practices Regulations 3. International Maritime Dangerous Goods Code (IMDG Code) 4. Emergency Procedures For Ships Carrying Dangerous Goods 5. Medical First Aid Guide for Use in Accidents Involving Goods (MFAG) 6. IMO BC Code - Code of Safe Practice for Solid Bulk Cargoes Poisoning and asphyxiation hazards
Certain bulk cargoes are liable to oxidation, which in t urn may result in oxygen depletion, emission of toxic fumes and self-heating. Other bulk cargoes may not oxidize but may emit toxic fumes. It is important therefore that the shipper inform the master before loading of the existence of any chemical hazards. The master should refer to Appendix B of the BC Code and take the necessary precautions, especially those pertaining to ventilation. Certain cargoes may emit toxic gases when wetted. In these cases the ship should be provided with the appropriate gas detection equipment. A flammable gas detector is only suitable for testing the explosive nature of gas mixtures. Emergency entry into a cargo space should be undertaken only by trained personnel wearing self-contained breathing apparatus, and protective clothing if considered necessary, always under the supervision of a responsible officer.
In the event of emergency entry into a cargo space, in addition to the above requirement, spare self-contained breathing apparatus, safety belts and safety lines should be readily available. Health hazard from dust
To minimize the chronic risks from exposure to the dust of certain materials carried in bulk, a high standard of personal hygiene for those exposed to the dust cannot be too strongly emphasized. The precautions should include not only the use of appropriate protective clothing and barrier creams when needed but also adequate personal washing especially before meals, and laundering of outer clothing. Flammable atmosphere
Dust created by certain cargoes may constitute an explosion hazard, especially, during loading, unloading and cleaning. This risk can be minimized at such times by ensuring that ventilation is sufficient to prevent the formation of a dustladen atmosphere and by hosing down rather than sweeping. CARGOES THAT MAY LIQUEFY (section 7 of the BC Code) Properties, characteristics and hazards
Cargoes that may liquefy include concentrates, certain coals and other materials having similar physical properties. Appendix A of the BC Code contains a list of such cargoes, which generally consist of a mixture of small particles in contrast with natural ores that include a considerable percentage of large particles or lumps. Section 5 of the BC Code - Trimming Procedures
At moisture content above that of the transportable moisture limit, shift of cargo may occur as a result of liquefaction. The major purpose of the sections of this Code dealing with these cargoes is to draw the attention of masters and others to the latent risk of cargo shift, and to describe the precautions deemed necessary to minimize this risk. Such cargoes may appear to be relatively dry and granular when loaded, but may contain sufficient moisture as to become fluid under the stimulus of compaction and the vibration that occurs during a voyage.
In the resulting viscous fluid state, cargo may flow to one side of the ship when it rolls one way, but not completely return when it rolls the other. Thus, the ship sways progressively until it reaches a dangerous heel and capsizes. To prevent subsequent shifting, and also to decrease the effects of oxidation of material with a predisposition to oxidize, these cargoes should be trimmed reasonably level on completion of loading, irrespective of the angle of repose.
Amended Extract from SOLAS Chapter VI Part B
Special provisions for bulk cargoes other than grain Regulation 6 Acceptability for shipment Concentrates or other cargoes which may liquefy shall only be accepted for loading when the actual moisture content of the cargo is less than its transportable moisture limit. However, such concentrates and other cargoes may be accepted for loading even when their moisture content exceeds the above limit, provided that safety arrangements to the satisfaction of the Administration are made to ensure adequate stability in the case of cargo shifting and further provided that the ship has adequate structural integrity. Prior to loading a bulk cargo which is not a cargo classified but which has chemical properties that may create a potential hazard, special precautions for its safe carriage shall be taken. Regulation 7 Loading, unloading and stowage of bulk cargoes To enable the master to prevent excessive stresses in the ship’s structure, the ship shall be provided with a booklet, which shall be written in a language with which the ship’s officers responsible for cargo operations are familiar. The booklet shall, as a minimum, include: .1 stability data, .2 ballasting and de-ballasting rates and capacities; .3 maximum allowable load per unit surface area of the tank top plating; .4 maximum allowable load per hold; .5 general loading and unloading instructions with regard to the strength of the ship’s structure including any limitations on the most adverse operating conditions during loading, unloading, ballasting operations and the voyage; .6 any special restrictions such as limitations on the most adverse operating conditions imposed by the Administration or organization recognized by it, if applicable; and
.7 where strength calculations are required, maximum permissible forces and moments on the ship’s hull during loading, unloading and the voyage. Before a solid bulk cargo is loaded or unloaded, the master and the terminal representative shall agree on a plan* which shall ensure that the permissible forces and moments on the ship are not exceeded during loading or unloading, and shall include the sequence, quantity and rate of loading or unloading, taking into consideration the speed of loading or unloading, the number of pours and the de-ballasting or ballasting capability of the ship. The plan and any subsequent amendments thereto shall be lodged with the appropriate authority of the port State. Bulk cargoes shall be loaded and trimmed reasonably level, as necessary, to the boundaries of the cargo space so as to minimize the risk of shifting and to ensure that adequate stability will be maintained throughout the voyage. When bulk cargoes are carried in ‘tween-decks, the hatchways of such ‘tween-decks shall be closed in those cases where the loading information indicates an unacceptable level of stress of the bottom structure if the hatchways are left open. The cargo shall be trimmed reasonably level and shall either extend from side to side or be secured by additional longitudinal divisions of sufficient strength. The safe load-carrying capacity of the ‘tweendecks shall be observed to ensure that the deck-structure is not overloaded. The master and terminal representative shall ensure that loading and unloading operations are conducted in accordance with the agreed plan. If during loading or unloading any of the limits of the ship are exceeded or are likely to become so if the loading or unloading continues, the master has the right to suspend operation and the obligation to notify accordingly the appropriate authority of the port State with which the plan has been lodged. The master and the terminal representative shall ensure that corrective action is taken. When unloading cargo, the master and terminal representative shall ensure that the unloading method does not damage the ship’s structure. The master shall ensure that ship’s personnel continuously monitor cargo operations. Where possible, the ship’s draught shall be checked regularly during loading or unloading to confirm the tonnage figures supplied. Each draught and tonnage observation shall be recorded in a
cargo logbook. If significant deviations from the agreed plan are detected, cargo or ballast operations or both shall be adjusted to ensure that the deviations are corrected. At a moisture content above that of the transportable moisture limit, shift of cargo may occur as a result of liquefaction. Many cargoes may appear to be relatively dry and granular when loaded, but may contain sufficient moisture as to become fluid under the stimulus of compaction and the vibration that occurs during a voyage. In the resulting viscous fluid state, cargo may flow to one side of the ship when it rolls one way, but not completely return when it rolls the other. Thus, the ship way progressively reaches a dangerous heel and capsize. Ships other than specialist suited ones shall carry only those cargoes having a moisture content that is not in excess of the transportable moisture limit as defined in this Code. Specially suited ships
Specially suited ships may carry concentrates having a moisture content in excess of the transportable moisture limit if the ship possesses a valid document of approval from her administration, accompanied by such stability information as her administration may require. The document of approval must clearly state “For carriage of concentrates having a moisture content in excess of the transportable moisture limit”. When concentrates are loaded that have a moisture content in excess of the transportable moisture limit, the whole surface area of each cargo space shall be trimmed level. Cargoes having a moisture content in excess of the flow moisture point shall not be carried in bulk. Before loading, the shipper or his appointed agents shall provide to the master and the port warden, if requested, details, as appropriate, of the characteristics and properties of any material constituting bulk cargo, such as flow moisture point, stowage factor, moisture content, angle of repose, chemical hazards, etc. so that any necessary safety precautions can be put into effect. To do this the shipper shall arrange, possibly in consultation with the producers, for the cargo to be properly sampled and tested. Furthermore, the shipper should provide the ship’s
master and the port warden, if requested, with the appropriate certificates of test, as applicable for a given cargo. Before and during loading, auxiliary check tests of the moisture content may be carried out using instruments designed specifically for that purpose, such as the “SPEEDY MOISTURE TESTER”. Tests conducted with this instrument indicate a precision of ±1% compared with the laboratory method, i.e., with a laboratory reading of 10%, the “SPEEDY” reading could range from, 9% to 11%. If the readings obtained by this method are consistently higher than those shown on the certificate, loading of the cargo should cease and a further laboratory test be conducted. If the master has doubts as regards the appearance of condition of the cargo for safe shipment, the following auxiliary method may be used on board ship or at the dockside to perform a check test for approximately determining the possibility of flow: Half fill a cylindrical can or similar container (0.5-1 litre capacity) with a sample of cargo. Take the can in one hand and bring it down sharply from a height of about 0.2m to strike a hard surface such as a solid table. Repeat the procedure twenty-five times at one or two second intervals. Examine the surface for free moisture or fluid conditions. If free moisture or a fluid condition appears, make arrangements to have additional laboratory tests on the cargo conducted before it is accepted for loading.
COAL is very liable to spontaneous heating. If there is sufficient oxygen available, combustion is liable to take place. The amount of heating that takes place depends on the type of type coal and how much heat can be dispersed by ventilating the coal. Ventilation can be a double-edged weapon as although it takes heat from the coal it also allows unwanted oxygen into the coal. To keep the coal as cool as possible it should be stowed away from hot bulkheads. To keep oxygen away from the coal only surface ventilation should be allowed. All spar ceiling or cargo battening should be removed as besides the liability of it to damage, it can give unwanted air pockets in the coal. Unwanted air may also get into a cargo through a temporary wooden bulkhead. If such a bulkhead has been constructed all cracks should be sealed, preferably by pasting paper over both sides of the bulkhead. Freshly mined coal absorbs oxygen, which, with extrinsic moisture, forms peroxides. These in turn breakdown to form carbon monoxide and carbon dioxide. Heat is produced by this exothermic reaction causing further oxidation and further heat. If this heat is not dissipated ignition will occur. This is called Spontaneous combustion. As this is essentially a surface reaction the smaller the surface available for the absorption of oxygen the better. Every attempt should be made to prevent undue breakage of the coal whilst it is being loaded. It may be noted that 1 MT of coal in an unbroken cube has a surface area of about 3.72m2, whereas if it is broken up to pass through a 1.5mm mesh screen its surface area is nearly 4000m2. If a large amount of breakage occurs the small coal with the large surface area is found in the centre of the hold, whilst the large coal will roll down the sides. This aggravates the situation, as the large coal gives a good path for air to flow to the smaller coal where the spontaneous heating is most liable to occur. Most coal fires in cargo occur at about ‘tween deck level and this is the area where the greatest attention should be paid to temperature and the restriction of through ventilation.
The following are recommendations for the carriage of coal. The ventilators to the lower holds should be so arranged that they might be opened or closed at will during the voyage. As the critical temperature at which the process of spontaneous heating in coal becomes greatly accelerated is in some varieties of coal as low as 36˚C, and generally is not much higher, the need of keeping the exteriors surface of the hull, and thereby the interior of the ‘tween decks and holds, as cool as possible is manifest. The iron decks of ships carrying coal in the tropics can be covered with dunnage to lessen heating. Suitable means should be provided for ascertaining from time to time the temperature of the lower mass of coal, particularly below the hatchways, and this might be done by means of two pipes leading down to the bottom of the coal at each hatchway. The temperature tubes should have closed ends to prevent admission of air into the cargo. The temperature of the coal at three heights should be taken daily.
Gas from the holds or ‘tween decks space may find its way into shaft, peaks, chain lockers or similar space unless the bulkheads and casings are maintained in gas tight conditions. Naked lights should not be used in holds or other spaces in which gas may accumulate until the spaces have been well ventilated. Full use should, when necessary, be made of the breathing apparatus or smoke helmet and the safety lamp, which form part of the ship’s statutory fire appliances. The employment of the crew in chipping and painting below decks during the voyage should be avoided. The danger from smoking should be realized and no oily waste, wood, old rope, sacking etc. should be left below where it can become ignited by spontaneous heating On arrival at the port of discharge the hold ventilators should be unplugged and the lower hold well ventilated before commencing to work cargo. Coal is frequently loaded from a single tip and earlier it was necessary to drift the vessel fore and aft so that all holds may be filled. To keep these shifts to a minimum No.2 was first put under the tip. After about one third the capacity of the hold was loaded the vessel was shifted so that No. 3 was loaded to about one third of its capacity. Likewise the remaining after holds were loaded and then the tip was shifted astern to reach No. 1, half the capacity was put in, before shifting to No. 2, which was then filled. The other after holds were now filled in order excepting the aftermost. The aftermost hold and the No.1 were now worked so that the vessel would complete loading in a good trim. Coal is sometimes graded, when this in so, care should be taken to prevent undue breakage. Lowering the first few truckloads into the hold helps as do control of the rate of tipping down and chute. Some ports have conveyor belts and an endless bucket system for loading; this is excellent for graded coal and also keeps the dust down with the ordinary coal. Fortunately it is mainly the better coals, which are graded, and in generally these are not so friable.
Coal will need to be trimmed and its angle of repose is quite high, especially if large coal is loaded. There is no danger for coal shifting unless it is the very small stuff known as mud coal, slurry or duff. This is very fine coal, almost dust, and if the moisture content is high it behaves almost like a liquid.
Bulk Cargo (Grain)
Loading and Stowage of Bulk Grain
Before loading bulk the following preparations should be done: Holds and tween deck thoroughly swept down. All dunnage removed from cargo spaces or stowed at one and covered. Bilges should be cleaned and sweetened Bilges suctions should be tested Tween deck scuppers should be covered with double weave separation cloth, edges to be fixed with cement. Any cracks between limber boards to be covered with separation cloth nailed down to prevent the cargo from going into the bilges. All pipelines passing through the bilges should be tested and any leaks discovered should be fixed – esp. fire mains, water ballast lines and bilge pumping out lines. After the holds are swept and if required hosed down, the holds/ compartments are to be inspected for any infestation. The inspection should include all easily accessible areas together with inaccessible areas including under the beams and hatch pontoon frames. In case fumigation is carried out prior loading then the compartment has to be swept and again inspected for any dead insects and rodents. The fumigant used should be compatible with the cargo to be carried.
For loading of Rice the fumigation may be carried out twice – prior loading and on completion of discharging. The inspection for infestation should be very thorough since apart from later claims, some ports especially in the US, the USDA inspectors would have to clear the ship for loading – and these inspectors are known to be very thorough. Shifting of cargo Certain bulk cargos have a tendency to shift and precautions must be taken to counteract this tendency. These precautions are dealt with below: Recommendation are made about the stowage of the cargo: Weight =
db (3L+B)
tonnes
4.6 where d is the summer load draft b is average breadth of lower hold L is length of lower hold B is the maximum moulded breadth The height of the cargo pile peak should not exceed: 1.89 x d x S. F. (m3/tonne) metres Angle of repose
This is the greatest angle from the horizontal to which a substance can be raised without it shifting. Cargoes most liable to shift are those having a small angler of repose. Angle of repose of 35˚ is taken as being the dividing line for bulk cargoes of lesser or greater shifting hazard and cargoes having angles of repose of more or less than this figure are considered separately. Trimming
In compartments entirely filled with bulk grain the grain shall be trimmed so as to fill all the spaces between the beams and in the wings and ends. In compartments partly filled with bulk grain the grain shall be levelled whenever practicable.
The provision of a shifting boards or longitude bulkheads within 5% of the vessel’s moulded breadth from the centre line or two or more longitudinal bulkheads or shifting boards with a distance between of not more than 60% of the vessel’s moulded breadth. In the latter case suitable sized trimming hatches are to be provided in the wings at intervals of not more than 7.62m., the end hatches being not more than 3.66m from transverse bulkheads. In holds the shifting boards must extend downwards from the deck at least 2. 44m or ½ depth of hold whichever is the greater. In ‘tween decks and in feeders, unless there is some exemption they must extend from deck to deck. If the compartment is only partly filled with grain, the shifting boards must extend from the bottom of the compartment to at 0.6m above the surface of the bulk grain, however no shifting boards are necessary if the bulk grain does not occupy more than ½ of the hold or ½ of the hold where there is a shaft tunnel. The Shifting boards must not be less than 50mm in thickness and are to have a 80mm housing at the bulkhead. They must be adequately supported by wood minimum size 250mm x 50mm or metal uprights with a maximum spacing of 3.96mm and set in 80mm housings top and bottom. The jointing of 50mm shifting boards must overlap by at least 230mm in way of the uprights. If the uprights are made sufficiently strong and the length is not too great, shoring or staying may be unnecessary. If wood shores are used they must be in a single piece securely fixed at each end and heeled against the permanent structure of the ship, but not directly against the side plating. The angle between the shore and the horizontal should be kept as small as possible and must never exceed 45˚. The size of the shore is dependent upon its length; a shore over 6.1m in length would be at least 200m x 150mm. If stays are used they will be fitted horizontally and will consist of 75mm – 6 x 12 galvanised flexible steel wire rope, secured with 25mm shackles to uprights and frames and fitted with 32mm rigging screws in accessible positions. If the uprights are not secured at the top, the uppermost shore or stay is to be not less than 0.46m from the top. The vertical spacing of the shores or stays is obtained from tables in the rules. GM
If a GM after correction for FSC of not less than 0.31m is maintained throughout the voyage in one or two deck ships or 0.36m in other ships longitudinal bulkheads or shifting boards are not required in the following positions, (except when linseed in bulk is being carried therein) Below and within 2.13m of a feeder which contains not less than 5% of the quantity of grain in the space it feeds, but only in way a hatchway, In feeders as above provided that the free grain surface will remain within the feeders throughout the voyage allowing for a sinkage of 2% of the volume of the compartment fed and a shift of the free grain surface to 12˚, In way of the hatchway where the bulk grain has been saucered, provided that the hatchway is filled with bagged grain or other suitable bagged cargo. The minimum depth of the bagged cargo in the centre of the saucer to be 1.83m below the deck level. The grains to be stored tightly up to the deck head in the other parts of the compartment, In way of a hatchway in a compartment partly filled with bulk grain.
The surface of grain in a partly filled compartment is to be saucered with a minimum height of 1.52m of bagged grain or other suitable cargo over the portion where there are no shifting boards and 1.22m where there are shifting boards. This latter height is also required
when the bulk grain does not occupy more than 1/3 of the hold or ½ of the hold where there is a shaft tunnel.
The bagged grain shall be carried in sound bags, which shall be securely closed and well filled. The bags or other suitable cargo shall be supported on suitable platforms which consist of strong separation cloths with adequate overlapping or 25mm boards spaced not more that 100mm apart laid on bearers not more than 1.22m apart. Feeders are to be fitted to feed compartments entirely filled with bulk grain, except in deep tanks not over ½ moulded breadth of vessel in case ‘GM c’ above. They are to contain not less than 2% of the quantity of grain carried in the compartment, which they feed. The boarding may be horizontal or vertical but must be sufficiently supported by binders, shores or stays as laid down in the rules. Feeding holes are to be provided about 0.61m apart in coamings, which extend more that 0.39m below the deck. The diameter of the hole is 50mm or 88mm depending on coaming depth. Feeders are assumed to be capable of feeding a distance of 7.62m.
If any part of the compartment is more that 7.62m (measured in a fore and aft line) from the nearest feeder, the grain in the space beyond 7.62m is to be levelled off at a depth of at least 1.83m below the deck and the space above is to be filled with bagged grain or suitable cargo. Loading two different cargoes in the same hold Very occasionally, different types of grain are loaded into the same hold. The heavier grain is loaded first and trimmed level over the entire area of the hold. The surface is covered with separation cloths/ canvas, allowing for ample overlaps, at least 1m. The cloths are carried well up the sides and ends of the compartment so that the next grain loaded will force them against the plating between the frames and stiffeners, it has to be ensured that adequate leeway is allowed for the separation cloth being taken up the sides and ends of the compartment, since the lower cargo would settle down during the voyage and if this leeway is not allowed for the cloth would exert a pull and tear off from the side moorings. This would result in the cargo being mixed. The lighter grain should be loaded carefully at first to avoid displacing the separation cloths. Once the lighter cargo has been leveled off to a height of 0.5m all over the loading may begin at the usual rate, care being taken to see that it is constantly leveled by adjusting the loading chute inflow direction. When bulk grain is carried in the ‘tween deck of a two deck ship or in the upper ‘tween deck of a ship having more than two decks or above deck the following are to be complied with:
Either the GM shall not be less than that specified in paragraph ‘GM’ or the total quantity of bulk grain or other cargo carried in the specified space shall not exceed 28% by weight of the total cargo below the ‘tween deck. Partly filled deck area in the above space is not to exceed 93m2, The spaces which contain bulk grain are to be divided into lengths of not more than 30.5m by transverse bulkheads, or if not so divided the excess space – beyond 30.5m is to be entirely filled with bagged grain or other suitable cargo. Vessels having a GM less than that specified in paragraph ‘GM’ are not permitted to have more than two holds or compartments partly filled with bulk grain wherein the overstowing cargo does not fill the space to the deck head. Feeders are not compartments and so they are exempted from this requirement. Double bottom tanks used to meet a stability requirement are to be adequately subdivided longitudinally unless the width of the tank at its ½ length does not exceed 60% of the vessel’s moulded breadth. A grain-loading plan may be supplied to certain ships, which may then be exempted from some of the provisions outlined above due to their special construction (such as tanker and bulk carriers), which prevents shifting of the bulk cargo. However, the resulting list of the vessel must not exceed 5˚ if the grain settles by 2% and shifts to an angle of 12˚ from its original position.
Cargo Care
Inspection of Holds prior Loading: All holds should be inspected prior commencing loading this may be done while the ship is enroute or just after completion of discharging and prior loading at the same port.
A thorough cleaning of the hold is undertaken; the bilges are cleaned and tried out with an amount of water. If required the hold is hosed down and the water pumped to holding tanks. This ensures that there is no refuse lying within the holds and that the bilges after loading would if necessary be capable of being pumped out. The bilges if with offensive smell have to be sweetened. This is again a necessity to prevent any food cargo from being tainted. All other lines in the hold are to be pressed up and checked for leaks. Air pipes and sounding pipes passing through the hold spaces are to be checked up with a head of water. The above ensures that ingress of water into the hold is minimized. The hold bottom has to be inspected for any dents in the plating. Some DB’s may be dedicated for fuel oil/ ballast as such this would give a fair idea if the plates have set in or if their appears to be a deep indentation/ All spar dunnage at the ship sides are to be fitted and the frames at the sides have to be inspected. This is done so that if bale cargo is loaded the shipside steel does not come in contact with the cargo. The used lashing material has to be removed including all temporary eyes, which had been made. And if this is not done then the same eyes may be inadvertently be used for new lashing – lashing wires are for one use only and the risk of parted lashing arises by using old lashings. Use of Dunnage
There are basically a few reasons why dunnage is so necessary on general cargo ships while loading general cargo. Of prime importance is to keep the cargo away from the steel bottom of the hold. The steel bottom condenses the moisture in the air and these droplets of moisture over a period of time can damage cargo. This is known as ship sweat. And only by dunnage can the cargo be
safeguarded against this. Good ventilation certainly helps but some amount of sweat is ever present. The second reason why dunnage is spread about on the holds is to bring about some amount of frictional resistance between the cargo and the steel bottom. Thus lashing becomes easier. Another factor is the dunnage helps in spreading the cargo weight evenly. In the event of small ingress of water the dunnage helps in channeling the water into the bilge wells, if this were not prevented then any accidental ingress of water would be absorbed or retained in pools by the cargo. If the hold bottom is dirty due to stain and hard coating of earlier cargo and hosing down is not possible then a double layer of dunnage would prevent the cargo in coming into contact with the stain. In general holds are laid with double dunnage while tween decks are layered with single dunnage. The size of the dunnage may vary but usually they are about 6” X 1” X 6 feet. These are laid about 6” to 10” apart, though the gaps may again vary depending upon the nature of the cargo. The bottom tier of the hold dunnaging may be laid in the fore and aft direction and the top tier in the athwart ship direction. At the aft of the hold a clearing of two feet is laid with the bottom tier in the athwart ship direction. This helps in the water/ condensation from trickling to aft and then subsequently finding the bilge well. Tween deck dunnaging is of one tier – exceptionally may be two tiers and it really doesn’t make much difference if the dunnage is laid out in the fore and aft direction or in the athwart ship direction. For heavy cargo where spreading the weight takes precedence over other hazards, the dunnage or timber used is generally 4” X 4” X 6 feet (they may be also of stouter variety). These heavy timbers are laid out in the fore and aft direction in order that the load is spread on as many frame spaces as possible. Dunnaging also forms a very important factor when ventilation is of primary concern especially when loading a consignment of Rice. Extra channels are created within the bagged cargo to allow good ventilation. Together with double dunnaging being provided between
stacks of 4-6 bags. If this is not done then the cargo sweat that may be generated is not removed and condenses on the cargo itself allowing the cargo to rot. Dunnage is used primarily for the protection of the cargo from sweat related damage and consequently it is used so that the cargo does not get too closely packed thereby obstructing to the flow of air. Special cargoes use more dunnage where air channels have to be kept so that the airflow is not hampered. Rice is one such cargo. Advantage of dunnaging is also from the fact that it spreads the weight of the cargo evenly all across the tank top or tween deck top, but this advantage is a side benefit, the main reason is protection from sweat. And to some extent from heat from the boiler spaces in the engine room. Dunnage is thus primarily for the prevention of sweat damage to cargo. The structure of the ship is made of steel, this steel being a good conductor of heat cools down faster than wood as such the temperature of the steel may fall below the dew point of the air within the compartment leading to sweat. However if this steel can be prevented from coming into contact with the cargo by a layer of wood, which being a poor conductor of heat does not cool down so drastically, then the effect of the sweat coming into contact with the cargo and thus damaging the same may be limited.
If despite precautions being taken, sweating does occur, the damage caused may be minimized by adequate dunnaging of the boundaries of the compartment.
The permanent dunnage of the ships side is known as SPAR Ceiling or CARGO BATTENS. It consists of timber about 150mm x 50mm fitted over the side frames. It is usually fitted horizontally into cleats on the frames. There is a vertical distance of not more than 230mm between the battens. On some ships the spars are fitted vertically and this gives better protection to the cargo as well as it suffers less damage and is thus more long lasting. Spar ceiling may also be fitted on the bulkheads at the ends of the compartment; this is especially the case where the bulkhead is the engine room bulkhead.
The tank top should be covered with a double layer of dunnage. The bottom layer is usually 100mm x 50mm or 150mm x 50mm spaced about 300mm apart and laid athwart ships to ensure free drainage to the bilges. If the ship has only bilge wells then it is preferable to lay the dunnage in the fore and aft direction. The upper layer consists of 25mm boards about 150mm in width laid at right angles to the bottom layer, about 150mm - 300mm apart. Occasionally burlap/Hessian is laid over the dunnage - this improves the appearance of the hold but restricts air circulation through the cargo, A permanent wooden ceiling more than 65mm thick is often laid on the tank top in the square of the hatch; this is to protect the tank top and does not replace the dunnaging. A similar arrangement of dunnage will be found in the tween decks, although double dunnaging is not so commonly found here. Care should be taken to have a good layer of dunnage at the ship’s side over the stringer plate, as water tends to accumulate there.
Secondhand timber is frequently used for dunnage. It should always be inspected to ensure that it is free of stains, odour, nails and large splinters. New timber also has its drawbacks; it should be free of resin and should not have a strong smell of new wood. The top of the cargo is protected by a covering (especially under the stringer plate) by matting, wood dunnage or some sort of waterproof paper, or plastic sheets.
Single Fore and Aft dunnaging the most common dunnaging:
The second Layer
Contamination of Cargo Cargoes -which taint easily, e.g. tea, flour, sugar, should be kept well away from strong smells. If a pungent (strong smelling) cargo e.g. cloves, cinnamon has been carried previously, deodorizing of the compartment will be necessary. Dirty Cargoes should never be carried in the same compartment as “clean” cargoes. A very general classification for “dirty” cargoes could include paints and oils, steelwork, animal products other than foodstuffs. Similarly a general classification of clean cargo could
include food products and manufactured vegetable products e.g. clothing. Naturally there will be exceptions to both of the above groups. Reasons for a general inspection of holds All holds should be inspected prior commencing loading this may be done while the ship is enroute or just after completion of discharging and prior loading at the same port. A thorough cleaning of the hold is undertaken; the bilges are cleaned and tried out with an amount of water. If required the hold is hosed down and the water pumped to holding tanks. This ensures that there is no refuse lying within the holds and that the bilges after loading would if necessary be capable of being pumped out. The bilges if with offensive smell have to be sweetened. This is again a necessity to prevent any food cargo from being tainted. All other lines in the hold are to be pressed up and checked for leaks. Air pipes and sounding pipes passing through the hold spaces are to be checked up with a head of water. The above ensures that ingress of water into the hold is minimized. The hold bottom has to be inspected for any dents in the plating. Some DB’s may be dedicated for fuel oil/ ballast as such this inspection would give a fair idea if the plates have set in or if their appears to be a deep indentation. All spar dunnage at the ship sides are to be fitted and the frames at the sides have to be inspected. This is done so that if bale cargo is loaded the shipside steel does not come in contact with the cargo. The used lashing material has to be removed including all temporary eyes, which had been made. And if this is not done then the same eyes may be inadvertently be used for new lashing lashing wires are for one use only and the risk of parted lashing arises by using old lashings.
Bilge and Suction Wells
Bilges and bilge wells should be thoroughly cleaned prior loading any cargo and especially if the previous cargo was oil cakes or such other cargo. Bilges should be cleaned, the suctions tried out and then the bilges should be sweetened with pine oil or such. The bilges should be finally dried. Prior loading of cargo all bilge wells should be cleaned and then filled with water and the water then pumped out. Timings for pumping out the water should be noted and compared with the pump efficiency. While filling the bilge well the sounding as measured by the sounding rod should be checked against the actual as observed inside the bilge well. The sounding pipe should be checked for any blockage. The striker plate underneath the sounding pipe also should be checked for wear down. Deep Tanks
Deep tanks are tanks on general cargo ships, which are accessible from the hold. The lines leading to such tanks are to be blanked off since a slight leakage in such lines can damage cargo in the holds. The man holes to these tanks also has to be ensured that they are water tight. If any liquid is loaded then the thermometer conduits should be checked for any leakage as well the heating coils have to be tested prior loading. The pumping out arrangement has to be tried out before hand. Covering of Bilge Wells
These suction filters are very easily taken care of. Hessian is used to form a pad comprising of a double layer and this is wrapped around the loose filter covers of the drain wells. The pad should not be so thick that it would absorb water and prevent the water from draining into the wells. For limber boards the same pads are nailed down between the adjacent boards. And they then serve the same purpose, that is prevent any debris from clogging up the suctions. Care of Ballast Lines
This is very important, since the inadvertent ballasting of the deep tanks would damage cargo loaded in the deep tanks.
There are many instances of the above happening, bulk carriers of yesteryears often had a hold dedicated as a water ballast tank, in 1978 a new ship off the building yard in Gothenburg had not blanked off the ballast lines since the line had a double segregation. The vessel proceeded to load grain in a US port and on arriving at a UK port for discharging her cargo, it was found that a substantial amount of cargo in the mentioned hold had become damaged due to leakage of water from the ballast lines. Separation Of Cargo
Separation of cargo for the above cases is required to prevent claims arising due to short landing and later complications with port authorities and customs for cargo left behind on a ship for which duty is payable There may be numerous ways of separating cargoes bound for different ports or for same port and different consignees. In general though not all are any hard and fast rule the principle is to ensure that cargoes destined for a particular port or consignee is delivered accordingly. Failure to do this at the time of loading would create chaos at the discharging port, with short landings – residual cargo, since the excess cargo that would remain would not be permitted to be discharged in a subsequent port without creating more paperwork and expenditure. In fact cases have arisen where ships have been arrested for landing cargo not destined for that port – customs take a very strict view of this in many parts of the world. Thus it is of paramount importance to ensure that cargoes are efficiently separated and marked so that to an un-initiated the cargo discharge may proceed smoothly. Port markings may be made by different means for different cargoes, the following are some of the few: Hessian separation strips, in various colours – used to encircle the parcel Shoring, blocking and securing the later port cargo, since this would have to be done in any case at the discharging port. Paper sheets Lashing ropes with coloured strips of cloth wrapped around the joints-turnbuckles/ shackles/ bulldog clips.
Different cargo used as a separation between two similar cargoes. Water based colours used as port marking or consignee marking – this method though is used more often for consignee marking. Where bare steel cargo is loaded oil based paint is also sometimes used, since the others may not be suitable due to partial rusting of the plates as well that hessian strips are inefficient for these cargoes. Valuable Cargo
Valuable cargo such as Banknotes or mail earlier used to be carried on general cargo ships in special lockers. If such lockers were not available then some dedicated space, which could be effectively secured, was made available. Newer ships do not have such allotted spaces and today most cargoes of such nature is shipped in containers. Personal effects are also shipped and unless stated as very valuable is loaded in ordinary holds and are quickly over stowed with other cargo. As long as the over stowage is incomplete the hold is strictly watched and the watchman is done away with once the cargo is over stowed and the entrance to the hold is locked. All mail and personal effects are tallied on board – by shore staff as well by a ships staff, the results are then verified. In case of any dispute the authorities are informed before a general protest is made. Ventilation
On general cargo ships one of the largest number of cargo claims is made for goods, which, have been damaged in transit. Barring breakages and handling damage the most common damage is caused by sweat. SWEAT is formed when the water vapour in the air condenses out into water droplets when the air is cooled below its dew point. The water droplets may be deposited onto the ship’s structure known as “ship’s sweat” or on to the cargo known as “cargo sweat”. Ship’s sweat may run down, and may also drip onto the cargo. Cargo sweat occurs when the cargo is cold and the incoming air is warm. Cargo sweat that is formed may be absorbed by the cargo or if steel may run down after rusting the cargo.
To avoid sweat and its effects it is imperative that wet and dry bulb temperatures of the air entering and the air contained in the cargo compartment are taken at frequent intervals (once a watch). If the temperature of the outside air is less than the dew point of the air already in the compartment, sweating will occur. This gives rise to ship sweat and is most usually found on voyages from warm places to colder places. Especially in winter, on voyages from Singapore to Northern China. Similarly if the temperature of the air in the compartment (or the cargo) is lower than the dew point of the incoming air sweating will again occur. This gives rise to cargo sweat and usually occurs on voyage from cold to warmer places. Especially in winter, on voyages from Northern China to Singapore. If the latter of the foregoing conditions is encountered ventilation from the outside air should be stopped until more favourable conditions obtain. It should be noted that indiscriminate ventilation often does more harm than no ventilation whatsoever. It should also be noted that variation in the angles of the ventilators from the wind cause very different rates of airflow within the compartment. The angle, which the ship’s course makes with the wind, also affects the flow of air. In general the greatest airflow occurs when the lee ventilators are trimmed on the wind and the weather ventilators are trimmed away from the wind.
Showing air circulation with lee vents on the wind and weather vents off. This is THROUGH VENTILATION. If the dew point temperature of the air in the hold can be kept below the temperature of the ship’s structure (decks, sides and bulkheads) and the cargo, there will be no danger of sweat forming. This condition cannot always be achieved without some means of mechanically circulating and drying the air in the hold. With mechanical ventilation baffle plates are fitted in the hold and tween deck ventilators, so that air can be prevented from the outside when conditions are unfavourable. At these times the air in the hold is re-circulated and, if necessary, it can be dried by passing it through a de- humidifying unit. It must be emphasized that the best results can only be obtained from these systems when air temperatures and dew points are carefully observed and the maker’s instructions followed implicitly. The adequate ventilation of container cargoes poses many problems and experiments have been made with portable ventilation units fitted into the individual containers. However, it
would appear the most common practice is to give through ventilation for the container compartments and hope that the ventilator grilles on the side of the containers give the correct flow air over the contents. It may be pointed out that vastly different types of cargo may be loaded in adjacent containers in the ‘cell’ stowage and in most cases the ship’s personnel are unaware of the contents of individual containers. Refrigerated cargo
The cleanliness of cargo compartments for the transport of refrigerated foodstuffs is more important than for any other cargoes. Failure to clean properly can result in mould growth and rotting of fruit and vegetables. Spaces are swept down and all loose dirt removed. Any remaining residues of previous cargoes will have to be scraped or washed off. After cleaning, the spaces are sprayed with a mild disinfectant such as weak sodium hypochlorite solution, which also helps to remove odours. Alternatively, an ozoniser may be used for the same purpose, especially after the carriage of a strong-smelling cargo like oranges. Holds and lockers are then cooled to carriage temperature. It is essential that any dunnage to be used is placed in the space before pre-cooling, since the use of warm dunnage could cause considerable damage. It is common practice to have holds and refrigerating machinery inspected by an independent surveyor to certify that the ship is in a fit condition for the carriage of the intended cargo. The cargo should be inspected ashore by the ship’s officers before loading to see that it is in good condition and has been properly pre-cooled where that is required. A sample of the cargo should be thoroughly inspected for signs of mould or other damage and its temperature checked by inserting a steel-tipped thermometer into the product. A record of the inspection and temperatures recorded should be kept. Similar random inspections of the cargo should be made during the loading. Any damaged products or carcasses which have thawed should be rejected or loaded separately. They could cause spoiling of the remainder of the cargo which was in good condition. The carriage temperatures are stipulated by the shipper of the goods and should be adhered to as closely as possible. Temperatures are taken and recorded at frequent regular intervals and entered in a log-book. Many ships are also equipped with thermographs, which provide a continuous record of compartment temperatures. In the event of claims for cargo damage,
the records and thermograph charts will be required as evidence that the correct temperatures were maintained. In general cargo ships with a limited amount of refrigerated space it is usual to arrange, as far as possible, for the refrigerated cargo to be loaded last and at its destination to be discharged first. When refrigerated cargo is to be, carried, specially insulated compartments must be provided. The insulation on the sides, top and bottom of the compartment may be of cork, fiberglass wool or polyurethane rigid foam. It will be retained in position by galvanised sheeting. The cooling may be effected by either circulating cold brine (relative density 1.047) through pipes on the sides and deck head, or by blowing cold air through the compartment. The compartment must be scrupulously clean when loading meat and dairy products. It is recommended that after sweeping out, the compartment is wiped down with cloths wrung out in a cleansing fluid; this will prevent the formation of mould on woodwork. If a fruit or other strong smelling cargo has been carried in the compartment previously, it will also be necessary to deodorize it. Spaces are swept down and all loose dirt removed. Any remaining residues of previous cargoes will have to be scraped or washed off. After cleaning, the spaces are sprayed with a mild disinfectant such as weak sodium hypochlorite solution, which also helps to remove odours. Alternatively, an ozoniser may be used for the same purpose, especially after the carriage of a strong-smelling cargo like oranges. The bilges should be cleaned and sweetened and their suctions tested. The brine traps should be cleaned out, refilled and tested. This also applies to those in the ‘tween deck. The brine traps serve a dual purpose they prevent the cold air from reaching the bilges and thus freezing out the water in the pipes and also they prevent the bad odour from the bilges reaching the cold chambers. If the vessel is fitted with brine-pipes the side baffle boards (which keep the cargo clear of the pipes) should be removed and the pipes wiped clean. If fitted with the cold air circulation system, air ducts should be cleaned, this is particularly important if a dusty cargo has been carried previously. Any fat or grease spots on the deck should be scraped up.
The insulation should be inspected and any repairs necessary to it or to the sparring, which is attached to it, must be effected. Thermometers should, be made ready and, where fitted, thermometer pipes should be erected. Any ventilators leading to the compartment must be plugged. Air change plugs should also be in position. Dunnage must be pre-cooled before use. In most-trades the dunnage will be laid before the loading commences. If the compartment is fitted with gratings, these will have been scrubbed before being laid down. When chilled meat is to be carried, the requisite number of meat bars, hooks and chain will have to be placed in the compartment for pre-cooling. The hook and chains should be sterilized (this is usually done ashore). When the compartment has been prepared it will be cooled to the loading temperature. It will then be ready for the surveyor to carry out a loading port survey. In most cases this is in essential before any cargo is loaded. When the cargo has been loaded the portable brine-pipes will be fitted in the. square of the hatch. Afterwards the insulated plug hatches must be shipped and fitted as tightly as possible. It is frequently necessary to paste paper over the joints to keep the hatch as airtight as possible. In extreme cases the joints may have to be caulked and pitched. In the latter case, the greatest. care must be taken when opening up as pitch and oakum falling onto carcass meat can stain it. When general cargo or frozen cargo at a different temperature is being carried in the deck above, a layer of sawdust is often put over the hatches and deck to absorb any condensation. Occasionally it may be necessary to load cargo through a ‘tween deck which contains refrigerated cargo. The refrigeration should be stopped whilst the hatches are open,
otherwise an undue amount of frost may form. If this forms on brine pipes it will act as insulation and prevent further cooling. Refrigerated containers with their own built in cooling units are to be inspected as thoroughly as for chambers above – that is if they are being stuffed on board, this is extremely rare. In general the containers are pre-cooled ashore and then are stuffed at the providers place or in the dock from refrigerated trucks. The inspections are done by shore surveyors. Prior loading all the ships power points for these containers are to be tested and logged down. While receiving the containers the containers are to be inspected for any dents or gashes on the body and the temperature card (circular) is to be noted. The temperature is to be noted, however the temperature may a bit high on loading and it comes down after the ships power is switched on. The temperature graph is to be monitored and any sign of heating up is to be prevented. Some units have drawings to do some sort of emergency arrangements if the unit fails during the voyage. The graph card needs to be renewed once the time scale gets over and these are kept as spare on board and are to be replaced by fresh cards, the filled in cards are to be kept with the cargo/ chief officer for handing them ashore prior discharging. Temperature records are vital in both the methods of carriage. Temperatures are to be recorded at least three times a day and all the points provided and the same is to be recorded, if automatic recorders are provided then the visual sightings also should be used for checking. For containers too the same procedure is to be followed, visual sightings are recorded together with the automatic recording. All records are to be kept safely are to be handed over (copies) to the shore authorities after discharging. These records are vital in case there are claims about the cargo and the temperature records are the only proof the ship has to refute the claims. Prior loading the cargo in pallets are to be inspected (non containerized) by ships officer together with the surveyor. Often the cargo is brought to the jetty and the packages may
show signs of softening (thaw) these are to be rejected. Also depending on the shippers agreeing the temperature probes (which may puncture the cases) may be inserted to note the temperature, this however may not be allowed since they apparently damage the cases (paper hardboard). Any staining of the cases again is to be investigated and rejected if necessary. Reefer cargo is loaded last and discharged first. All cargo is tallied on board and ashore since some are liable for pilferage – shrimps as such.
Dangerous Goods
Classes, divisions, packing groups Definitions Substances (including mixtures and solutions) and articles subject to the provisions of this Code are assigned to one of the classes 1 -9 according to the hazard or the most predominant of the hazards they present. Some of these classes are subdivided into divisions. These classes or divisions are as listed below: Class 1: Explosives Division 1.1: substances and articles, which have a mass explosion hazard Division 1.2: substances and articles, which have a projection, hazard but not a mass explosion hazard Division 1.3: substances and articles, which have a fire hazard and either a minor blast hazard or a minor projection hazard or both, but not a mass explosion hazard Division 1.4: substances and articles, which present no significant hazard Division 1.5: very insensitive substances, which have a mass explosion hazard Division 1.6: extremely insensitive articles which do not have a mass explosion hazard Class 2: Gases Class 2.1: flammable gases Class 2.2: non-flammable, non-toxic gases
Class 2.3: toxic gases Class 3: Flammable liquids Class 4: Flammable solids; substances liable to spontaneous combustion; substances which, in contact with water, emit flammable gases Class 4.1: flammable solids, self-reactive substances and desensitized explosives Class 4.2: substances liable to spontaneous combustion Class 4.3: substances, which, in contact with water, emit flammable gases Class 5: Oxidizing substances and organic peroxides Class 5.1: oxidizing substances Class 5.2: organic peroxides Class 6: Toxic and infectious substances Class 6.1: toxic substances Class 6.2: infectious substances Class 7: Radioactive material Class 8: Corrosive substances Class 9: Miscellaneous dangerous substances and articles The numerical order of the classes and divisions is not that of the degree of danger. Marking, labelling and placarding
Packages containing dangerous goods shall be durably marked with the correct technical name; trade names alone shall not be used. Packages containing dangerous goods shall be provided with distinctive labels or stencils of the labels, or placards, as appropriate, so as to make clear the dangerous properties of the goods contained therein. The method of marking the correct technical name and of affixing labels or applying stencils of labels, or of affixing placards on packages containing dangerous goods, shall be such that this information will still be identifiable on packages surviving at least three months’ immersion in the sea. In considering suitable marking, labelling and placarding methods,
account shall be taken of the durability of the materials used and of the surface of the package. Packages containing dangerous goods shall be so marked and labeled except that: .1 packages containing dangerous goods of a low degree of hazard or packed in limited quantities or .2 when special circumstances permit, packages that are stowed and handled in units that are identified by labels or placards; may be exempted from labelling requirements. General information prior loading/ discharging The duty officer entrusted with the loading of the dangerous goods should have all the relevant data regarding the dangerous goods that would be loaded, these would include: Copy of the document from the shipper regarding the cargo Classification of the DG Quantity to be loaded Proposed stowage Type of packages Shipping name – that is the correct technical name Segregation required from other cargo as well as from other DG MFAG and EmS requirement for the safe handling of the cargo Any fire hazard as per IMDG Any temperature/ wetness restriction for the loading of the cargo UN Numbers and Proper Shipping Names Dangerous goods are assigned to UN Numbers and Proper Shipping Names according to their hazard classification and their composition. Dangerous goods commonly transported are listed in the Dangerous Goods List. Where an article or substance is specifically listed by name, it should be identified in transport by the Proper Shipping Name in the Dangerous Goods List. For dangerous goods not specifically
listed by name, “generic” or “not otherwise specified” entries are provided to identify the article or substance in transport. Each entry in the Dangerous Goods List is assigned a UN Number. This list also contains relevant information for each entry, such as hazard class, subsidiary risk(s) (if any), packing group (where assigned), packing and tank transport provisions, EmS, segregation and stowage, properties and observations, etc. Entries in the Dangerous Goods List are of the following four types: Single entries for well-defined substances or articles e.g. UN 1090 acetone UN 1194 ethyl nitrite solution Generic entries for well-defined groups of substances or articles e.g. UN 1133 adhesives UN 1266 perfumery product Information on the special measures to be taken when a certain dangerous cargo is handled Additionally the chief officer should have attached relevant extracts from the IMDG code in particular all the emergencies that could arise with the handling of the cargo. Also the emergency clean-up measures as well as the first aid requirement as per the EmS (Emergency Schedule of the IMDG) and MFAG. Any special precautions mention as per the Dangerous List should be extracted. Compatibility risks should be ascertained. For example if the following cargo (class 3) is to be loaded, then: Stowage of goods of class 3 The vapours from all substances of class 3 have a narcotic effect, and prolonged inhalation may result in unconsciousness. Deep or prolonged narcosis may lead to death. Class 3 substances should be stowed as indicated in the Dangerous Goods List. However, substances with a flashpoint of 23˚C (c.c). or less packaged in jerricans, plastics (3Hl, 3H2),
drums, plastics (lHl,lH2) and plastics receptacles in a plastic drum (6HH1,6HH2)should be stowed on, deck only unless packed in a closed cargo transport unit. The substances of this class should be kept as cool as reasonably practicable during transit. They should, in general, be stowed “away from” all possible sources of heat. Adequate precautions should be taken to protect the flammable liquids from heat emanating from bulkheads or other sources. Ventilation should be provided which should effectively remove flammable vapours from the cargo space. Adequate measures should be taken to prevent the penetration of leaking liquid or vapour into any other part of the ship. Vapours may not necessarily be lighter than air and may sink to the lower levels of a cargo space where they may be accidentally ignited and a “flashback” to the flammable liquids may occur. Whenever flammable liquids with a flashpoint of 23˚C c.c. or less are transported in portable tanks, the stowage should be such that leaking vapours are unlikely to penetrate the accommodation, machinery spaces and other work areas via entrances or other openings in bulkheads or through ventilation ducts. Where it is deemed necessary for a substance of this class to be stowed “clear of living quarters”, it is included in the Dangerous Goods List. On ships carrying passengers, substances in this class should be stowed well away from any deck or spaces provided for the use of passengers. When such substances are transported on board roll-on/roll-off ships, see chapter 7.4. End extract Reporting of incidents involving dangerous goods
When an incident takes place involving the loss or likely loss overboard of packaged dangerous goods into the sea, the master, or other person having charge of the ship, shall report the particulars of such an incident without delay and to the fullest extent possible to the nearest coastal State. The report shall be based on the guidelines and general principles adopted by IMO for dangerous goods, harmful substances and/or marine pollutants. In the event of the ship referred to in paragraph 1 being abandoned, or in the event of a report from such a ship being incomplete or unobtainable, the owner, charterer, manager or
operator of the ship, or their agents shall, to the fullest extent possible, assume the obligations placed upon the master by this regulation. The duty officer when he discovers an incident or accident has to immediately raise the alarm and inform the Master regarding the same. The crew on deck should be the first to renders assistance as well as start the clean up operations as well as try to minimise the incident under the supervision of the duty officer as per the guidelines laid down for that cargo as per the IMDG code and the Dangerous cargo list. Actions to be taken All actions after an accident are to be as per the following documents – which have detailed instructions for all types of emergencies. The following gives a basic layout of a rescue scenario. The IMO/WHO/ILO Medical First Aid Guide for Use in Accidents Involving Dangerous Goods (MFAG) is the Chemicals Supplement to the International Medical Guide for Ships (IMGS), which is published by the World Health Organization (WHO), Geneva. The Maritime Safety Committee adopted this revised text of the Guide in May 1998, for use in association with Amendment 30-00 of the IMDG Code, and will be further amended as and when, necessary. Table 1 RESCUE Rescuers must be adequately protected from exposure before entering a contaminated area in order to avoid injury. When a chemical is unidentified, worst-case assumptions concerning toxicity must be assumed. ARRIVAL AT SCENE Upon arrival at the scene, an initial assessment of the situation should be made and the size of the incident should be determined. Rescuers must NOT:
Enter a contaminated area without using a pressure-demand self-contained breathing apparatus and wearing full protective clothing; Enter an enclosed space unless they are trained members of a rescue team and follow correct procedures; Walk through any spilled materials; Allow unnecessary contamination of equipment; Attempt to recover shipping papers or manifests from contaminated area unless adequately protected; Become exposed while approaching a potentially contaminated area; Attempt rescue unless trained and equipped with appropriate personal protective equipment (PPE) and protective clothing for the situation. QUICKLY ESTABLISH AN EXCLUSION OR HOT ZONE Assume that anyone leaving the exclusion zone is contaminated and should be assessed and decontaminated, if necessary. Do not remove non-ambulatory casualties from the exclusion zone unless properly trained personnel with the appropriate PPE are available and decontamination has been accomplished. INITIAL TRIAGE OF CASUALTIES (SORTING AND PRIORITY) One unconscious casualty Give immediate treatment to the unconscious casualty only, and Send for help. Several unconscious casualties If there
is more than one unconscious casualty:
Send for help, and Give appropriate treatment to the worst casualty in the priority order of: Casualties who have stopped breathing or have no pulse (see Table 2). Casualties who ARE UNCONCIOUS (see Table 4).
Casualty is unconscious but breathing If the casualty is unconscious or cyanotic (bluish skin) but breathing, connect to portable oxygen. Neck or back trauma Apply neck and back support before moving casualty if there is any question of neck or back trauma. Priority. Airway, Breathing, Circulation (A-B-C) Initial management of Airway, Breathing and Circulation (A-B-C, see table 2) is all that should be undertaken while there is potential for further injury to the casualty or to response personnel. Gross decontamination If the casualty is contaminated with chemicals, gross decontamination should be performed. Cut away or remove all suspected contaminated clothing, including jewellery and watches. Brush or wipe off any obvious contamination. Care should be taken to protect open wounds from contamination. Every effort should be made by personnel to avoid contact with potentially contaminated casualties. Rescuers should wear protective clothing, if necessary. Cover or wrap casualty to prevent spread of contamination. Removal of casualties from exclusion zone Once gross decontamination has been performed, the casualties should be removed from the exclusion zone. If casualties can walk, lead them out of the exclusion zone to an area where decontamination and further evaluation can take place. If casualties are unable to walk, remove them on stretchers. If stretchers are unavailable, carefully carry or drag casualties to an area where decontamination and further evaluation can take place. DECONTAMINATION Decontaminate from head down
Take care not to introduce contaminants into open wounds. Decontaminate exposed wounds and eyes before intact skin areas. Cover wounds with a waterproof dressing after decontamination.
For external contamination, begin with the least aggressive methods Limit mechanical or chemical irritation of the skin. Wash contaminated area gently under a stream of water for at least ten minutes, and wash carefully with soap and warm (never hot) water, scrubbing with a soft brush or surgical sponge. Reduce level of contaminants Remove contaminants to the level that they are no longer a threat to casualty or response personnel. Isolate the casualty from the environment to prevent the spread of any remaining contaminants. Contain runoff; bag contaminated clothing If possible, contain all runoff from decontamination procedures for proper disposal. Ensure that all potentially contaminated casualty clothing and belongings have been removed and placed in properly labelled bags. SUMMARY OF TREATMENT OF CASUALTIES Assign highest priorities to Airway, Breathing, Circulation (ABC) and then decontamination. Complete primary and secondary assessments as conditions allow. Obtain information on chemicals to which the casualty has been exposed from shipping papers, labels or other documents. If there are multiple casualties, direct attention to the most seriously affected individuals first. Treat symptoms and signs as appropriate and when conditions allow. Obtain RADIO MEDICAL ADVICE when conditions allow. Perform invasive procedures only in uncontaminated areas.
Reassess the casualty frequently, because many chemicals have latent physiological effects. Delay preventive measures until the casualty is decontaminated. TRANSFER TO SHIP’S HOSPITAL Casualties who have been stabilized (airway, breathing and circulation) and decontaminated can be transported to the ship’s hospital for further evaluation. Further advice: see IMDG appendix 1 Packing requirements as per the Dangerous Goods List of the IMDG Code Structure of the Dangerous Goods List. The Dangerous Goods List is divided into 18 columns. Among them the packing requirements are specified in column 8 and in column 9 Column 8 Packing Instructions: This column contains alpha – numeric codes, which refer to the relevant packing instructions. The packing instructions indicate the packagings (including large packagings) which may be used for the transport of substances and articles. A code including the letter ‘P’ refers to packing instructions for the use of packagings described in IMDG Chapters – 6.1, 6.2 or 6.3 A code including the letter ‘LP’ refers to packing instructions for the use of large packagings described in IMDG Chapters – 6.6 A code including the letter ‘BP’ refers to the bulk packagings described in IMDG Chapters – 4.3 When a code including the letters ‘P’, ‘LP’ or ‘BP’ is not provided, it means that the substance is not allowed in that type of packaging. When ‘N/R’ is included in this column, it means that the substance or article need not be packaged. Column 9 Special packing provisions: This column contains alphanumeric codes, which refer to the relevant special packing provisions specified in 4.1.4. The special packing provisions indicate the packagings (including large packagings).
A special packing provisions including the letters ‘PP’ refers to a special packing provision applicable to the use of a packing instruction bearing the code ‘P’ in 4.1.4.1 A special packing provision including the letter ‘L’ refers to a special packing provision applicable to a packing instruction bearing the code ‘LP’ in 4.1.4.3 Reporting if the suitability and integrity of packages is found to be suspect Documents In all documents relating to the carriage of dangerous goods by sea where the goods are named, the correct technical name of the goods shall be used (trade names alone shall not be used) and the correct description given in accordance with the classification. The shipping documents prepared by the shipper shall include, or be accompanied by, a signed certificate or declaration that the shipment offered for carriage is properly packaged and marked, labelled or placarded, as appropriate, and in proper condition for carriage. The persons responsible for the packing of dangerous goods in a freight container or road vehicle shall provide a signed container packing certificate or vehicle packing declaration stating that the cargo in the unit has been properly packed and secured and that all applicable transport requirements have been met. Such a certificate or declaration may be combined with the document above. Where there is due cause to suspect that a freight container or road vehicle in which dangerous goods are packed is not in compliance with the requirements, or where a container-packing certificate or vehicle packing declaration is not available, the freight container or vehicle shall not be accepted for shipment. Each ship carrying dangerous goods shall have a special list or manifest setting forth, in accordance with the classification, the dangerous goods on board and the location thereof. A detailed stowage plan, which identifies by class and sets out the location of all dangerous goods on board, may be used in place of such a special list or manifest. A copy of one of these documents shall be made available before departure to the person or organization designated by the port State authority. Cargo transport units, including freight containers, shall be loaded, stowed and secured throughout the voyage in accordance with the Cargo Securing Manual approved by the
Administration. The Cargo Securing Manual shall be drawn up to a standard at least equivalent to the guidelines developed by the IMO. The above are as per SOLAS. If the duty officer feels that there is some discrepancy between the document submitted and the markings on the cargo, he is to stop loading and inform the Master. If the packaging is suspect or if the duty officer feels that the packaging looks worn out or is not sufficient then again he is to stop the loading and inform the Master. General fire precautions The prevention of fire in a cargo of dangerous goods is achieved by practicing good seamanship, observing in particular the following precautions: I. keep combustible material away from ignition sources; II. protect a flammable substance by adequate packing; III. reject damaged or leaking packages; IV. stow packages protected from-accidental damage or heating; V. segregate packages from substances liable to start or spread fire; VI. where appropriate and practicable, stow dangerous goods in an accessible position so that packages in the vicinity of a fire may be protected; VII. enforce prohibition of smoking in dangerous areas and display clearly recognizable “NO SMOKING” notices or signs; and VIII. the dangers from short-circuits, earth leakages or sparking will be apparent. Lighting and power cables, and fittings should be maintained in good condition. Cables or equipment found to be unsafe should be disconnected. Where a bulkhead is required to be suitable for segregation purposes, cables and conduit penetrations of the decks and bulkheads should be sealed against the passage of gas and vapours. When stowing dangerous goods on deck, the position and design of auxiliary machinery, electrical equipment and cable runs should be considered in order to avoid sources of ignition.
Fire precautions applying to individual classes, and where necessary to individual substances, are recommended in following paragraphs and in the Dangerous Goods List. Special fire precautions for class 1 The greatest risk in the handling and transport of goods of class 1 is that of fire from a source external to the goods, and it is vital that any fire should be detected and extinguished before it can reach such goods. Consequently, it is essential that fire precautions, fire-fighting measures and equipment should be of a high standard and ready for immediate application and use. Compartments containing goods of class 1 and adjacent cargo spaces should be provided with a fire detection system. If such spaces are not protected by a fixed fire-extinguishing system, they should be accessible for fire-fighting operations. No repair work should be carried out in a compartment containing goods of class 1. Special care should be exercised in carrying out repairs in any adjacent space. No welding, burning, cutting, or riveting operations involving the use of fire, flame, spark, or arc-producing equipment should be carried out in any space other than machinery spaces and workshops where fire-extinguishing arrangements are available, except in any emergency and, if in port, with prior authorization of the port authority, Special fire precautions for class 2 Effective ventilation should be provided to remove any leakage of gas from within the cargo space or spaces, bearing in mind that some gases are heavier than air and may accumulate in dangerous concentrations in the lower part of the ship. Measures should be taken to prevent leaking gases from penetrating into any other part of the ship. If there is any reason to suspect leakage of a gas, entry into cargo spaces or other enclosed spaces should not be permitted until the master or responsible officer has taken all safety considerations into account and is satisfied that it is safe to do so. Emergency entry under other circumstances should only be undertaken by trained crew wearing self-contained breathing apparatus, and protective clothing when recommended, and always under the supervision of a responsible officer.
Leakage from receptacles containing flammable gases may give rise to explosive mixtures with air. Such mixtures, if ignited, may result in explosion and fire. Special fire precautions for class 3 Flammable liquids give off flammable vapours which, especially in an enclosed space, form explosive mixtures with air. Such vapours, if ignited, may cause a “flashback” to the place in which the substances are stowed. Due regard should be paid to the provision of adequate ventilation to prevent accumulation of vapours. Special fire precautions and fire fighting for class 7 The radioactive contents of Excepted, Industrial, and Type A packages are so restricted that, in the event of an accident and damage to the package, there is a high probability that any material released, or shielding efficiency lost, would not give rise to such radiological hazard as to hamper fire-fighting or rescue operations. Type B (U) packages, Type B (M) packages and Type C packages are designed to be strong enough to withstand severe fire without significant loss of contents or dangerous loss of radiation shielding. Precautions while loading discharging explosives Following are the emergency schedule1-01 with respect to explosives under Class 1 Division 1.1 Primary hazard: Explosive substances and articles, which may detonate all at once in a fire Associated hazards: Heavy debris and high speed fragments; possibility of the formation and escape of toxic fumes. Special Emergency equipment to be available: Protective clothing – gloves, fire resistant coveralls, fire mans helmet with visors SCBA Non sparking footwear Soft brushes and plastic trays – to pick up spillage Emergency procedures:
Wear non sparking footwear when dealing with spillage. Use SCBA and protective clothing when dealing with a spillage of materials having a subsidiary class 6.1 and or 8 label. Avoid sources of ignition – naked lights, unprotected light bulbs, electric hand tools, mechanical shock and friction. Use SCBA and protective clothing when dealing with fire. Understanding the nature of the precautions that have been laid down under the EmS (Emergency Schedule) it is important to note that all the above precautions need to be taken. Regarding whether water is to be kept available with a charged hose, is debatable as far as the cargo is concerned – however the likelihood of other non IMDG cargo catching fire does remain as such for the other cargo the fire mains may be utilized. Water if warranted by the IMDG code for the particular cargo may be used else it should not be used unless shipper says it is OK to use water or to cover spillage on deck with water. Additionally fire extinguishers – CO2 systems should be kept in readiness. The ship generally loads this type of cargo last – some ports have special anchorages or berths where such cargo is loaded, thus it is necessary to have the ship ready to leave berth in case of any fire. As such prior loading the ship should be ready to sail at a short notice.
Segregating of dangerous goods
Segregation
General The provisions of this chapter should apply to all cargo spaces on deck or under deck of all types of ships and to cargo transport units. The International Convention for the Safety of Life at Sea (SOLAS), 1974, as amended, requires in regulation 6.1 of part A of chapter VII that incompatible goods should be segregated from one another. For the implementation of this requirement, two substances or articles are considered mutually incompatible when their stowage together may result in undue hazards in case of leakage or spillage, or any other accident. The extent of the hazard arising from possible reactions between incompatible dangerous goods may vary and so the segregation arrangements required should also vary as appropriate. Such segregation is obtained by maintaining certain distances between incompatible dangerous goods or by requiring the presence of one or more steel bulkheads or decks between them, or a combination thereof. Intervening spaces between such dangerous goods may be filled with other cargo compatible with the dangerous substances in question. The following segregation terms are used throughout this Code: “Away from”; “Separated from”; “Separated by a complete compartment or hold from”; “Separated longitudinally by an intervening complete compartment or hold from”. The general provisions for segregation between the various classes of dangerous goods are shown in the segregation table”. In addition to the general provisions, there may be a need to segregate a particular substance, material or article from other goods, which could contribute to its hazard. Particular provisions for segregation are indicated in the Dangerous Goods List and, in the case of conflicting provisions, always take precedence over the general provisions.
For example: In the Dangerous Goods List entry for ACETYLENE, DISSOLVED, class 2.1, UN 1001, the following particular segregation requirement is specified: “separated from” chlorine In the Dangerous Goods List entry for BARIUM CYANIDE, class 6.1, UN 1565, the following particular segregation is specified: “separated from” acids Where the Code indicates a single secondary hazard (one subsidiary risk label), the segregation provisions applicable to that hazard should take precedence where they are more stringent than those of the primary hazard. Except for class 1, the segregation provisions for substances, materials or articles having more than two hazards (2 or more subsidiary risk labels) are given in the Dangerous Goods List. In the Dangerous Goods List entry for BROMINE CHLORIDE, class 2.3, UN 2901, subsidiary risks 5.1 and 8, the following particular segregation is specified: “segregation” as for class 5.1 but “separated from” class 7”. Segregation of packages Applicability The provisions of this subsection apply to the segregation of: packages containing dangerous goods and stowed in the conventional way; dangerous goods within cargo transport units; and dangerous goods stowed in the conventional way from those packed in such cargo transport units. Segregation of packages containing dangerous goods and stowed in the conventional way Definitions of the segregation terms Legend Reference package - BLUE
Package containing incompatible goods - RED Deck resistant to fire and liquid – BOLD LINE NOTE. Full vertical lines represent transverse bulkheads between cargo spaces (compartments or holds) resistant to fire and liquid.
Away from: Effectively segregated so that the incompatible goods cannot interact dangerously in the event of an accident but may be transported in the same compartment or hold or on deck, provided a minimum horizontal separation of 3 metres, projected vertically, is obtained.
Separated from: In different compartments or holds when stowed under deck. Provided the intervening deck is resistant to fire and liquid, a vertical separation i.e. in different compartments, may be accepted as equivalent to this segregation. For on deck stowage, this segregation means a separation by a distance of sit least 6 metres horizontally.
Separated by a complete compartment or hold from: Either a vertical or a horizontal separation. If the intervening decks are not resistant to fire and liquid,
then only a longitudinal separation, i.e. by an intervening complete
compartment or hold, is acceptable. For on deck stowage, this segregation means a separation by a distance of at least 12 metres horizontally. The same distance has to be applied if one package is stowed on deck and the other one in an upper compartment. Note: One of the two decks must be resistant to fire and to liquid.
Separated longitudinally by an intervening complete compartment or hold from: Vertical separation alone does not meet this requirement. Between a package under deck and one on deck, a minimum distance of 24 metres, including a complete compartment, must be maintained longitudinally. For on deck stowage, this segregation means a separation by a distance of at least 24 metres longitudinally.
Containment covered by the term “packaged form”
Chapter 4.1 describes the different types of packaging for use with goods under the IMDG code. Definitions Effectively closed: liquid-tight closure. Hermetically sealed: vapour-tight closure. Securely closed: so closed that dry contents cannot escape during normal handling; the minimum provisions for any closure. General provisions for the packing of dangerous goods, other than goods of classes 2, 6.2 or 7, in packagings, including Intermediate Bulk Containers (IBCs) and large packagings Dangerous goods should be packed in good quality packagings, including IBCs and large packagings, which should be strong enough to withstand the shocks and loadings normally encountered during transport, including trans-shipment between cargo transport units and/or warehouses as well as any removal from a pallet or overpack for subsequent manual or mechanical handling. Packagings, including IBCs and large packagings, should be constructed and closed so as to prevent any loss of contents when prepared for transport, which might be caused under normal conditions of transport, by vibration, or by changes in temperature, humidity or pressure (resulting from altitude, for example). No dangerous residue should adhere to the outside of packages, IBCs and large packagings during transport. These provisions apply, as appropriate, to new, re-used, reconditioned or remanufactured packagings and to new and re-used IBCs and large packagings. Parts of packagings, including IBCs and large packagings, which are in direct contact with dangerous goods: .1 should not be affected or significantly weakened by those dangerous goods; and .2 should not cause a dangerous effect, such as catalyzing a reaction or reacting with the dangerous goods. Where necessary, they should be provided with a suitable inner coating or treatment.
Unless provided elsewhere in this Code, each packaging, including IBCs and large packagings, except inner packagings, should conform to a design type successfully tested in accordance with the provisions in the IMDG code. When filling packagings, including IBCs and large packagings, with liquids, sufficient ullage (outage) should be left to ensure that neither leakage nor permanent distortion of the packaging occurs as a result of an expansion of the liquid caused by temperatures likely to occur during transport. Unless specific provisions are prescribed, liquids should not completely fill a packaging at a temperature of 55˚C. However, sufficient ullage should be left in an IBC to ensure that at the mean bulk temperature of 50˚C it is not filled to more than 98% of its water capacity. Inner packagings should be packed in an outer packaging in such a way that, under normal conditions of transport, they cannot break, be punctured or leak their contents into the outer packaging. Inner packagings that are liable to break or be punctured easily, such as those made of glass, porcelain or stoneware or of certain plastics, materials, etc., should be secured in outer packagings with suitable cushioning material. Any leakage of the contents should not substantially impair the protective properties of the cushioning material or of the outer packaging. Cushioning and absorbent material should be inert and suited to the nature of the contents. The nature and the thickness of the outer packagings should be such that friction during transport does not generate any heating likely to alter dangerously the chemical stability of the contents. Dangerous goods should not be packed together in the same outer packaging, or in large packagings, with dangerous or other goods if they react dangerously with each other and cause: .1
combustion and/or evolution of considerable heat;
.2
evolution of flammable, toxic or asphyxiant gases;
.3
the formation of corrosive substances; or
.4
the formation of unstable substances.
Unless otherwise specified in the Dangerous Goods List, packages containing substances should be hermetically sealed: .1
evolve flammable gases or vapour;
.2
may become explosive if allowed to dry;
.3
evolve toxic gases or vapour;
.4
evolve corrosive gases or vapour; or
.5
may react dangerously with the atmosphere.
Liquids may only be filled into inner packagings which have an appropriate resistance to internal pressure that may be developed under normal conditions of transport. Where pressure may develop in a package by the emission of gas from the contents (as a result of temperature increase or other cause), the packaging may be fitted with a vent, provided that the gas emitted will not cause danger on account of its toxicity, its flammability, the quantity released, etc. The vent should be so designed that, when the packaging is in the attitude in which it is intended to be transported, leakages of liquid and the penetration of foreign matter are prevented under normal conditions of transport. New, remanufactured or re-used packagings, including IBCs and large packagings, or reconditioned packagings and repaired IBCs should be capable of passing the tests prescribed in IMDG code. Before being filled and handed over for transport, every packaging, including IBCs and large packagings, should be inspected to ensure that it is free from corrosion, contamination or other damage and every IBC should be inspected with regard to the proper functioning of any service equipment. Any packaging which shows signs of reduced strength as compared with the approved design type should no longer be used or should be so reconditioned that it is able to withstand the design type tests. Any IBC which shows signs of reduced strength as compared with the tested design type should no longer be used or should be so repaired that it is able to withstand the design type tests.
Empty packagings, including IBCs and large packagings, that have contained a dangerous substance should be treated in the same manner as is required by this Code for a filled packaging, unless adequate measures have been taken to nullify any hazard.
Every packaging, including IBCS, intended to contain liquids should successfully undergo a suitable leak proofness test, and be capable of meeting the appropriate test level indicated in IMDG code for the various types of IBCs: .1
before it is first used for transport;
.2
after remanufacturing or reconditioning of any packaging, before it is re-used for
transport; .3 after the repair of any IBC, before it is re-used for transport. For this test, the packaging, or IBC, need not have its closures fitted. The inner receptacle of a composite packaging or IBC may be tested without the outer packaging, provided the test results are not affected. This test is not necessary for inner packagings of combination packagings or large packagings. Packagings, including IBCS, used for solids which may become liquid at temperatures likely to be encountered during transport should also be capable of containing the substance in the liquid state. Packagings, including IBCS, used for powdery or granular substances should be sift-proof or should be provided with a liner. Explosives, self-reactive substances and organic peroxides Unless specific provision to the contrary is made in this Code, the packagings, including IBCs and large packagings, used for goods of class 1, self-reactive substances of class 4.1 and organic peroxides of class 5.2 should comply with the provisions for the medium danger group (packing group 11).
Use of salvage packagings Damaged, defective or leaking packages or dangerous goods that have spilled or leaked may be transported in special salvage packagings. This does not prevent- the use of a bigger size of packagings of appropriate type and performance level. During transport, packagings, including IBCs and large packagings, should be securely fastened to or contained within the cargo transport unit, so that lateral or longitudinal movement or impact is prevented and adequate external support is provided. Additional general provisions for the use of IBCs When IBCs are used for the transport of liquids with a flashpoint of 61˚C (closed cup) or lower, or of powders liable to dust explosion, measures should be taken to prevent a dangerous electrostatic discharge. For rigid plastics IBCs and composite IBCs with plastics inner receptacles, unless otherwise approved by the competent authority, the period of use permitted for the transport of dangerous liquids should be five years from the date of manufacture of the receptacle except where a shorter period of use is prescribed because of the nature of the liquid to be transported. General provisions concerning packing instructions Packing instructions applicable to dangerous goods of classes 1 to 9 are specified in chapter 4.1. They are subdivided in three sub-sections depending on the type of packagings to which they apply: sub-section 4.1.4.1 for packagings other than IBCs and large packagings: these packing instructions are designated by an alphanumeric code comprising the letter “P”; sub-section 4.1.4.2
for IBCS; these are designated by an alphanumeric code comprising the
letters “IBC”; sub-section 4.1.4.3
for large packagings; these are designated by an alphanumeric code
comprising the letters “LP”. Special packing provisions may also be specified in the packing instruction for individual substances or articles. They are also designated by an alphanumeric code comprising the letters:
“PP”
for packagings other than IBCs and large packagings
“B”
for IBCs
“L”
for large packagings.
Column 8 of the Dangerous Goods List shows for each article or substance the packing instructions) that should be used. Column 9 indicates the special packing provisions applicable to specific substances or articles. Each packing instruction shows, where applicable, the acceptable single and combination packagings. For combination packagings, the acceptable outer packagings, inner packagings and, when applicable, the maximum quantity permitted in each inner or outer packaging are shown. Maximum net mass and maximum capacity are as defined in chapter 1.2.1. Where the packing instructions in this chapter authorize the use of a particular type of outer packaging in a combination packaging (such as 4G), packagings bearing the same packaging identification code followed by the letters “V”, “U” or “W” marked in accordance with the provisions of part 6 (such as “4GV”, “4GU” or “4GW”) may also be used under the same conditions and limitations applicable to the use of that type of outer packaging according to the relevant packing instructions. For example, a combination packaging marked with the packaging code “4GV” may be used whenever a combination packaging marked “4G” is authorized, provided the provisions in the relevant packing instruction regarding types of inner packagings and quantity limitations are respected. The capacity of gas cylinders should not exceed 450 litres. The capacity for gas receptacles should not exceed 1000 litres.
Dangerous Goods
Classes, divisions, packing groups Definitions Substances (including mixtures and solutions) and articles subject to the provisions of this Code are assigned to one of the classes 1 -9 according to the hazard or the most
predominant of the hazards they present. Some of these classes are subdivided into divisions. These classes or divisions are as listed below: Class 1: Explosives Division 1.1: substances and articles, which have a mass explosion hazard Division 1.2: substances and articles, which have a projection, hazard but not a mass explosion hazard Division 1.3: substances and articles, which have a fire hazard and either a minor blast hazard or a minor projection hazard or both, but not a mass explosion hazard Division 1.4: substances and articles, which present no significant hazard Division 1.5: very insensitive substances, which have a mass explosion hazard Division 1.6: extremely insensitive articles which do not have a mass explosion hazard Class 2: Gases Class 2.1: flammable gases Class 2.2: non-flammable, non-toxic gases Class 2.3: toxic gases Class 3: Flammable liquids Class 4: Flammable solids; substances liable to spontaneous combustion; substances which, in contact with water, emit flammable gases Class 4.1: flammable solids, self-reactive substances and desensitized explosives Class 4.2: substances liable to spontaneous combustion Class 4.3: substances, which, in contact with water, emit flammable gases Class 5: Oxidizing substances and organic peroxides Class 5.1: oxidizing substances Class 5.2: organic peroxides Class 6: Toxic and infectious substances Class 6.1: toxic substances -
Class 6.2: infectious substances Class 7: Radioactive material Class 8: Corrosive substances Class 9: Miscellaneous dangerous substances and articles The numerical order of the classes and divisions is not that of the degree of danger. Marking, labelling and placarding
Packages containing dangerous goods shall be durably marked with the correct technical name; trade names alone shall not be used. Packages containing dangerous goods shall be provided with distinctive labels or stencils of the labels, or placards, as appropriate, so as to make clear the dangerous properties of the goods contained therein. The method of marking the correct technical name and of affixing labels or applying stencils of labels, or of affixing placards on packages containing dangerous goods, shall be such that this information will still be identifiable on packages surviving at least three months’ immersion in the sea. In considering suitable marking, labelling and placarding methods, account shall be taken of the durability of the materials used and of the surface of the package. Packages containing dangerous goods shall be so marked and labeled except that: .1 packages containing dangerous goods of a low degree of hazard or packed in limited quantities or .2 when special circumstances permit, packages that are stowed and handled in units that are identified by labels or placards; may be exempted from labelling requirements. General information prior loading/ discharging The duty officer entrusted with the loading of the dangerous goods should have all the relevant data regarding the dangerous goods that would be loaded, these would include: Copy of the document from the shipper regarding the cargo Classification of the DG Quantity to be loaded
Proposed stowage Type of packages Shipping name – that is the correct technical name Segregation required from other cargo as well as from other DG MFAG and EmS requirement for the safe handling of the cargo Any fire hazard as per IMDG Any temperature/ wetness restriction for the loading of the cargo UN Numbers and Proper Shipping Names Dangerous goods are assigned to UN Numbers and Proper Shipping Names according to their hazard classification and their composition. Dangerous goods commonly transported are listed in the Dangerous Goods List. Where an article or substance is specifically listed by name, it should be identified in transport by the Proper Shipping Name in the Dangerous Goods List. For dangerous goods not specifically listed by name, “generic” or “not otherwise specified” entries are provided to identify the article or substance in transport. Each entry in the Dangerous Goods List is assigned a UN Number. This list also contains relevant information for each entry, such as hazard class, subsidiary risk(s) (if any), packing group (where assigned), packing and tank transport provisions, EmS, segregation and stowage, properties and observations, etc. Entries in the Dangerous Goods List are of the following four types: Single entries for well-defined substances or articles e.g. UN 1090 acetone UN 1194 ethyl nitrite solution Generic entries for well-defined groups of substances or articles e.g. UN 1133 adhesives UN 1266 perfumery product
Information on the special measures to be taken when a certain dangerous cargo is handled Additionally the chief officer should have attached relevant extracts from the IMDG code in particular all the emergencies that could arise with the handling of the cargo. Also the emergency clean-up measures as well as the first aid requirement as per the EmS (Emergency Schedule of the IMDG) and MFAG. Any special precautions mention as per the Dangerous List should be extracted. Compatibility risks should be ascertained. For example if the following cargo (class 3) is to be loaded, then: Stowage of goods of class 3 The vapours from all substances of class 3 have a narcotic effect, and prolonged inhalation may result in unconsciousness. Deep or prolonged narcosis may lead to death. Class 3 substances should be stowed as indicated in the Dangerous Goods List. However, substances with a flashpoint of 23˚C (c.c). or less packaged in jerricans, plastics (3Hl, 3H2), drums, plastics (lHl,lH2) and plastics receptacles in a plastic drum (6HH1,6HH2)should be stowed on, deck only unless packed in a closed cargo transport unit. The substances of this class should be kept as cool as reasonably practicable during transit. They should, in general, be stowed “away from” all possible sources of heat. Adequate precautions should be taken to protect the flammable liquids from heat emanating from bulkheads or other sources. Ventilation should be provided which should effectively remove flammable vapours from the cargo space. Adequate measures should be taken to prevent the penetration of leaking liquid or vapour into any other part of the ship. Vapours may not necessarily be lighter than air and may sink to the lower levels of a cargo space where they may be accidentally ignited and a “flashback” to the flammable liquids may occur. Whenever flammable liquids with a flashpoint of 23˚C c.c. or less are transported in portable tanks, the stowage should be such that leaking vapours are unlikely to penetrate the accommodation, machinery spaces and other work areas via entrances or other openings in bulkheads or through ventilation ducts.
Where it is deemed necessary for a substance of this class to be stowed “clear of living quarters”, it is included in the Dangerous Goods List. On ships carrying passengers, substances in this class should be stowed well away from any deck or spaces provided for the use of passengers. When such substances are transported on board roll-on/roll-off ships, see chapter 7.4. End extract Reporting of incidents involving dangerous goods
When an incident takes place involving the loss or likely loss overboard of packaged dangerous goods into the sea, the master, or other person having charge of the ship, shall report the particulars of such an incident without delay and to the fullest extent possible to the nearest coastal State. The report shall be based on the guidelines and general principles adopted by IMO for dangerous goods, harmful substances and/or marine pollutants. In the event of the ship referred to in paragraph 1 being abandoned, or in the event of a report from such a ship being incomplete or unobtainable, the owner, charterer, manager or operator of the ship, or their agents shall, to the fullest extent possible, assume the obligations placed upon the master by this regulation. The duty officer when he discovers an incident or accident has to immediately raise the alarm and inform the Master regarding the same. The crew on deck should be the first to renders assistance as well as start the clean up operations as well as try to minimise the incident under the supervision of the duty officer as per the guidelines laid down for that cargo as per the IMDG code and the Dangerous cargo list. Actions to be taken All actions after an accident are to be as per the following documents – which have detailed instructions for all types of emergencies. The following gives a basic layout of a rescue scenario. The IMO/WHO/ILO Medical First Aid Guide for Use in Accidents Involving Dangerous Goods (MFAG) is the Chemicals Supplement to the International Medical Guide for Ships (IMGS), which is published by the World Health Organization (WHO), Geneva.
The Maritime Safety Committee adopted this revised text of the Guide in May 1998, for use in association with Amendment 30-00 of the IMDG Code, and will be further amended as and when, necessary. Table 1 RESCUE Rescuers must be adequately protected from exposure before entering a contaminated area in order to avoid injury. When a chemical is unidentified, worst-case assumptions concerning toxicity must be assumed. ARRIVAL AT SCENE Upon arrival at the scene, an initial assessment of the situation should be made and the size of the incident should be determined. Rescuers must NOT: Enter a contaminated area without using a pressure-demand self-contained breathing apparatus and wearing full protective clothing; Enter an enclosed space unless they are trained members of a rescue team and follow correct procedures; Walk through any spilled materials; Allow unnecessary contamination of equipment; Attempt to recover shipping papers or manifests from contaminated area unless adequately protected; Become exposed while approaching a potentially contaminated area; Attempt rescue unless trained and equipped with appropriate personal protective equipment (PPE) and protective clothing for the situation. QUICKLY ESTABLISH AN EXCLUSION OR HOT ZONE Assume that anyone leaving the exclusion zone is contaminated and should be assessed and decontaminated, if necessary.
Do not remove non-ambulatory casualties from the exclusion zone unless properly trained personnel with the appropriate PPE are available and decontamination has been accomplished. INITIAL TRIAGE OF CASUALTIES (SORTING AND PRIORITY) One unconscious casualty Give immediate treatment to the unconscious casualty only, and Send for help. Several unconscious casualties If there
is more than one unconscious casualty:
Send for help, and Give appropriate treatment to the worst casualty in the priority order of: Casualties who have stopped breathing or have no pulse (see Table 2). Casualties who ARE UNCONCIOUS (see Table 4). Casualty is unconscious but breathing If the casualty is unconscious or cyanotic (bluish skin) but breathing, connect to portable oxygen. Neck or back trauma Apply neck and back support before moving casualty if there is any question of neck or back trauma. Priority. Airway, Breathing, Circulation (A-B-C) Initial management of Airway, Breathing and Circulation (A-B-C, see table 2) is all that should be undertaken while there is potential for further injury to the casualty or to response personnel. Gross decontamination If the casualty is contaminated with chemicals, gross decontamination should be performed. Cut away or remove all suspected contaminated clothing, including jewellery and watches. Brush or wipe off any obvious contamination.
Care should be taken to protect open wounds from contamination. Every effort should be made by personnel to avoid contact with potentially contaminated casualties. Rescuers should wear protective clothing, if necessary. Cover or wrap casualty to prevent spread of contamination. Removal of casualties from exclusion zone Once gross decontamination has been performed, the casualties should be removed from the exclusion zone. If casualties can walk, lead them out of the exclusion zone to an area where decontamination and further evaluation can take place. If casualties are unable to walk, remove them on stretchers. If stretchers are unavailable, carefully carry or drag casualties to an area where decontamination and further evaluation can take place. DECONTAMINATION Decontaminate from head down Take care not to introduce contaminants into open wounds. Decontaminate exposed wounds and eyes before intact skin areas. Cover wounds with a waterproof dressing after decontamination.
For external contamination, begin with the least aggressive methods Limit mechanical or chemical irritation of the skin. Wash contaminated area gently under a stream of water for at least ten minutes, and wash carefully with soap and warm (never hot) water, scrubbing with a soft brush or surgical sponge. Reduce level of contaminants Remove contaminants to the level that they are no longer a threat to casualty or response personnel.
Isolate the casualty from the environment to prevent the spread of any remaining contaminants. Contain runoff; bag contaminated clothing If possible, contain all runoff from decontamination procedures for proper disposal. Ensure that all potentially contaminated casualty clothing and belongings have been removed and placed in properly labelled bags. SUMMARY OF TREATMENT OF CASUALTIES Assign highest priorities to Airway, Breathing, Circulation (ABC) and then decontamination. Complete primary and secondary assessments as conditions allow. Obtain information on chemicals to which the casualty has been exposed from shipping papers, labels or other documents. If there are multiple casualties, direct attention to the most seriously affected individuals first. Treat symptoms and signs as appropriate and when conditions allow. Obtain RADIO MEDICAL ADVICE when conditions allow. Perform invasive procedures only in uncontaminated areas. Reassess the casualty frequently, because many chemicals have latent physiological effects. Delay preventive measures until the casualty is decontaminated. TRANSFER TO SHIP’S HOSPITAL Casualties who have been stabilized (airway, breathing and circulation) and decontaminated can be transported to the ship’s hospital for further evaluation. Further advice: see IMDG appendix 1 Packing requirements as per the Dangerous Goods List of the IMDG Code Structure of the Dangerous Goods List. The Dangerous Goods List is divided into 18 columns. Among them the packing requirements are specified in column 8 and in column 9
Column 8 Packing Instructions: This column contains alpha – numeric codes, which refer to the relevant packing instructions. The packing instructions indicate the packagings (including large packagings) which may be used for the transport of substances and articles. A code including the letter ‘P’ refers to packing instructions for the use of packagings described in IMDG Chapters – 6.1, 6.2 or 6.3 A code including the letter ‘LP’ refers to packing instructions for the use of large packagings described in IMDG Chapters – 6.6 A code including the letter ‘BP’ refers to the bulk packagings described in IMDG Chapters – 4.3 When a code including the letters ‘P’, ‘LP’ or ‘BP’ is not provided, it means that the substance is not allowed in that type of packaging. When ‘N/R’ is included in this column, it means that the substance or article need not be packaged. Column 9 Special packing provisions: This column contains alphanumeric codes, which refer to the relevant special packing provisions specified in 4.1.4. The special packing provisions indicate the packagings (including large packagings). A special packing provisions including the letters ‘PP’ refers to a special packing provision applicable to the use of a packing instruction bearing the code ‘P’ in 4.1.4.1 A special packing provision including the letter ‘L’ refers to a special packing provision applicable to a packing instruction bearing the code ‘LP’ in 4.1.4.3 Reporting if the suitability and integrity of packages is found to be suspect Documents In all documents relating to the carriage of dangerous goods by sea where the goods are named, the correct technical name of the goods shall be used (trade names alone shall not be used) and the correct description given in accordance with the classification. The shipping documents prepared by the shipper shall include, or be accompanied by, a signed certificate or declaration that the shipment offered for carriage is properly packaged and marked, labelled or placarded, as appropriate, and in proper condition for carriage.
The persons responsible for the packing of dangerous goods in a freight container or road vehicle shall provide a signed container packing certificate or vehicle packing declaration stating that the cargo in the unit has been properly packed and secured and that all applicable transport requirements have been met. Such a certificate or declaration may be combined with the document above. Where there is due cause to suspect that a freight container or road vehicle in which dangerous goods are packed is not in compliance with the requirements, or where a container-packing certificate or vehicle packing declaration is not available, the freight container or vehicle shall not be accepted for shipment. Each ship carrying dangerous goods shall have a special list or manifest setting forth, in accordance with the classification, the dangerous goods on board and the location thereof. A detailed stowage plan, which identifies by class and sets out the location of all dangerous goods on board, may be used in place of such a special list or manifest. A copy of one of these documents shall be made available before departure to the person or organization designated by the port State authority. Cargo transport units, including freight containers, shall be loaded, stowed and secured throughout the voyage in accordance with the Cargo Securing Manual approved by the Administration. The Cargo Securing Manual shall be drawn up to a standard at least equivalent to the guidelines developed by the IMO. The above are as per SOLAS. If the duty officer feels that there is some discrepancy between the document submitted and the markings on the cargo, he is to stop loading and inform the Master. If the packaging is suspect or if the duty officer feels that the packaging looks worn out or is not sufficient then again he is to stop the loading and inform the Master. General fire precautions The prevention of fire in a cargo of dangerous goods is achieved by practicing good seamanship, observing in particular the following precautions: I. keep combustible material away from ignition sources; II. protect a flammable substance by adequate packing;
III. reject damaged or leaking packages; IV. stow packages protected from-accidental damage or heating; V. segregate packages from substances liable to start or spread fire; VI. where appropriate and practicable, stow dangerous goods in an accessible position so that packages in the vicinity of a fire may be protected; VII. enforce prohibition of smoking in dangerous areas and display clearly recognizable “NO SMOKING” notices or signs; and VIII. the dangers from short-circuits, earth leakages or sparking will be apparent. Lighting and power cables, and fittings should be maintained in good condition. Cables or equipment found to be unsafe should be disconnected. Where a bulkhead is required to be suitable for segregation purposes, cables and conduit penetrations of the decks and bulkheads should be sealed against the passage of gas and vapours. When stowing dangerous goods on deck, the position and design of auxiliary machinery, electrical equipment and cable runs should be considered in order to avoid sources of ignition. Fire precautions applying to individual classes, and where necessary to individual substances, are recommended in following paragraphs and in the Dangerous Goods List. Special fire precautions for class 1 The greatest risk in the handling and transport of goods of class 1 is that of fire from a source external to the goods, and it is vital that any fire should be detected and extinguished before it can reach such goods. Consequently, it is essential that fire precautions, fire-fighting measures and equipment should be of a high standard and ready for immediate application and use. Compartments containing goods of class 1 and adjacent cargo spaces should be provided with a fire detection system. If such spaces are not protected by a fixed fire-extinguishing system, they should be accessible for fire-fighting operations. No repair work should be carried out in a compartment containing goods of class 1. Special care should be exercised in carrying out repairs in any adjacent space. No welding, burning, cutting, or riveting operations involving the use of fire, flame, spark, or arc-producing
equipment should be carried out in any space other than machinery spaces and workshops where fire-extinguishing arrangements are available, except in any emergency and, if in port, with prior authorization of the port authority, Special fire precautions for class 2 Effective ventilation should be provided to remove any leakage of gas from within the cargo space or spaces, bearing in mind that some gases are heavier than air and may accumulate in dangerous concentrations in the lower part of the ship. Measures should be taken to prevent leaking gases from penetrating into any other part of the ship. If there is any reason to suspect leakage of a gas, entry into cargo spaces or other enclosed spaces should not be permitted until the master or responsible officer has taken all safety considerations into account and is satisfied that it is safe to do so. Emergency entry under other circumstances should only be undertaken by trained crew wearing self-contained breathing apparatus, and protective clothing when recommended, and always under the supervision of a responsible officer. Leakage from receptacles containing flammable gases may give rise to explosive mixtures with air. Such mixtures, if ignited, may result in explosion and fire. Special fire precautions for class 3 Flammable liquids give off flammable vapours which, especially in an enclosed space, form explosive mixtures with air. Such vapours, if ignited, may cause a “flashback” to the place in which the substances are stowed. Due regard should be paid to the provision of adequate ventilation to prevent accumulation of vapours. Special fire precautions and fire fighting for class 7 The radioactive contents of Excepted, Industrial, and Type A packages are so restricted that, in the event of an accident and damage to the package, there is a high probability that any material released, or shielding efficiency lost, would not give rise to such radiological hazard as to hamper fire-fighting or rescue operations.
Type B (U) packages, Type B (M) packages and Type C packages are designed to be strong enough to withstand severe fire without significant loss of contents or dangerous loss of radiation shielding. Precautions while loading discharging explosives Following are the emergency schedule1-01 with respect to explosives under Class 1 Division 1.1 Primary hazard: Explosive substances and articles, which may detonate all at once in a fire Associated hazards: Heavy debris and high speed fragments; possibility of the formation and escape of toxic fumes. Special Emergency equipment to be available: Protective clothing – gloves, fire resistant coveralls, fire mans helmet with visors SCBA Non sparking footwear Soft brushes and plastic trays – to pick up spillage Emergency procedures: Wear non sparking footwear when dealing with spillage. Use SCBA and protective clothing when dealing with a spillage of materials having a subsidiary class 6.1 and or 8 label. Avoid sources of ignition – naked lights, unprotected light bulbs, electric hand tools, mechanical shock and friction. Use SCBA and protective clothing when dealing with fire. Understanding the nature of the precautions that have been laid down under the EmS (Emergency Schedule) it is important to note that all the above precautions need to be taken. Regarding whether water is to be kept available with a charged hose, is debatable as far as the cargo is concerned – however the likelihood of other non IMDG cargo catching fire does remain as such for the other cargo the fire mains may be utilized. Water if warranted by the IMDG code for the particular cargo may be used else it should not be used unless shipper says it is OK to use water or to cover spillage on deck with water.
Additionally fire extinguishers – CO2 systems should be kept in readiness. The ship generally loads this type of cargo last – some ports have special anchorages or berths where such cargo is loaded, thus it is necessary to have the ship ready to leave berth in case of any fire. As such prior loading the ship should be ready to sail at a short notice.
Segregating of dangerous goods
Segregation
General The provisions of this chapter should apply to all cargo spaces on deck or under deck of all types of ships and to cargo transport units. The International Convention for the Safety of Life at Sea (SOLAS), 1974, as amended, requires in regulation 6.1 of part A of chapter VII that incompatible goods should be segregated from one another. For the implementation of this requirement, two substances or articles are considered mutually incompatible when their stowage together may result in undue hazards in case of leakage or spillage, or any other accident. The extent of the hazard arising from possible reactions between incompatible dangerous goods may vary and so the segregation arrangements required should also vary as appropriate. Such segregation is obtained by maintaining certain distances between incompatible dangerous goods or by requiring the presence of one or more steel bulkheads or decks between them, or a combination thereof. Intervening spaces between such dangerous goods may be filled with other cargo compatible with the dangerous substances in question. The following segregation terms are used throughout this Code: “Away from”; “Separated from”; “Separated by a complete compartment or hold from”; “Separated longitudinally by an intervening complete compartment or hold from”. The general provisions for segregation between the various classes of dangerous goods are shown in the segregation table”. In addition to the general provisions, there may be a need to segregate a particular substance, material or article from other goods, which could contribute to its hazard. Particular provisions for segregation are indicated in the Dangerous Goods List and, in the case of conflicting provisions, always take precedence over the general provisions.
For example: In the Dangerous Goods List entry for ACETYLENE, DISSOLVED, class 2.1, UN 1001, the following particular segregation requirement is specified: “separated from” chlorine In the Dangerous Goods List entry for BARIUM CYANIDE, class 6.1, UN 1565, the following particular segregation is specified: “separated from” acids Where the Code indicates a single secondary hazard (one subsidiary risk label), the segregation provisions applicable to that hazard should take precedence where they are more stringent than those of the primary hazard. Except for class 1, the segregation provisions for substances, materials or articles having more than two hazards (2 or more subsidiary risk labels) are given in the Dangerous Goods List. In the Dangerous Goods List entry for BROMINE CHLORIDE, class 2.3, UN 2901, subsidiary risks 5.1 and 8, the following particular segregation is specified: “segregation” as for class 5.1 but “separated from” class 7”. Segregation of packages Applicability The provisions of this subsection apply to the segregation of: packages containing dangerous goods and stowed in the conventional way; dangerous goods within cargo transport units; and dangerous goods stowed in the conventional way from those packed in such cargo transport units. Segregation of packages containing dangerous goods and stowed in the conventional way Definitions of the segregation terms Legend Reference package - BLUE
Package containing incompatible goods - RED Deck resistant to fire and liquid – BOLD LINE NOTE. Full vertical lines represent transverse bulkheads between cargo spaces (compartments or holds) resistant to fire and liquid.
Away from: Effectively segregated so that the incompatible goods cannot interact dangerously in the event of an accident but may be transported in the same compartment or hold or on deck, provided a minimum horizontal separation of 3 metres, projected vertically, is obtained.
Separated from: In different compartments or holds when stowed under deck. Provided the intervening deck is resistant to fire and liquid, a vertical separation i.e. in different compartments, may be accepted as equivalent to this segregation. For on deck stowage, this segregation means a separation by a distance of sit least 6 metres horizontally.
Separated by a complete compartment or hold from: Either a vertical or a horizontal separation. If the intervening decks are not resistant to fire and liquid,
then only a longitudinal separation, i.e. by an intervening complete
compartment or hold, is acceptable. For on deck stowage, this segregation means a separation by a distance of at least 12 metres horizontally. The same distance has to be applied if one package is stowed on deck and the other one in an upper compartment. Note: One of the two decks must be resistant to fire and to liquid.
Separated longitudinally by an intervening complete compartment or hold from: Vertical separation alone does not meet this requirement. Between a package under deck and one on deck, a minimum distance of 24 metres, including a complete compartment, must be maintained longitudinally. For on deck stowage, this segregation means a separation by a distance of at least 24 metres longitudinally.
Containment covered by the term “packaged form”
Chapter 4.1 describes the different types of packaging for use with goods under the IMDG code. Definitions Effectively closed: liquid-tight closure. Hermetically sealed: vapour-tight closure. Securely closed: so closed that dry contents cannot escape during normal handling; the minimum provisions for any closure. General provisions for the packing of dangerous goods, other than goods of classes 2, 6.2 or 7, in packagings, including Intermediate Bulk Containers (IBCs) and large packagings Dangerous goods should be packed in good quality packagings, including IBCs and large packagings, which should be strong enough to withstand the shocks and loadings normally encountered during transport, including trans-shipment between cargo transport units and/or warehouses as well as any removal from a pallet or overpack for subsequent manual or mechanical handling. Packagings, including IBCs and large packagings, should be constructed and closed so as to prevent any loss of contents when prepared for transport, which might be caused under normal conditions of transport, by vibration, or by changes in temperature, humidity or pressure (resulting from altitude, for example). No dangerous residue should adhere to the outside of packages, IBCs and large packagings during transport. These provisions apply, as appropriate, to new, re-used, reconditioned or remanufactured packagings and to new and re-used IBCs and large packagings. Parts of packagings, including IBCs and large packagings, which are in direct contact with dangerous goods: .1 should not be affected or significantly weakened by those dangerous goods; and .2 should not cause a dangerous effect, such as catalyzing a reaction or reacting with the dangerous goods. Where necessary, they should be provided with a suitable inner coating or treatment.
Unless provided elsewhere in this Code, each packaging, including IBCs and large packagings, except inner packagings, should conform to a design type successfully tested in accordance with the provisions in the IMDG code. When filling packagings, including IBCs and large packagings, with liquids, sufficient ullage (outage) should be left to ensure that neither leakage nor permanent distortion of the packaging occurs as a result of an expansion of the liquid caused by temperatures likely to occur during transport. Unless specific provisions are prescribed, liquids should not completely fill a packaging at a temperature of 55˚C. However, sufficient ullage should be left in an IBC to ensure that at the mean bulk temperature of 50˚C it is not filled to more than 98% of its water capacity. Inner packagings should be packed in an outer packaging in such a way that, under normal conditions of transport, they cannot break, be punctured or leak their contents into the outer packaging. Inner packagings that are liable to break or be punctured easily, such as those made of glass, porcelain or stoneware or of certain plastics, materials, etc., should be secured in outer packagings with suitable cushioning material. Any leakage of the contents should not substantially impair the protective properties of the cushioning material or of the outer packaging. Cushioning and absorbent material should be inert and suited to the nature of the contents. The nature and the thickness of the outer packagings should be such that friction during transport does not generate any heating likely to alter dangerously the chemical stability of the contents. Dangerous goods should not be packed together in the same outer packaging, or in large packagings, with dangerous or other goods if they react dangerously with each other and cause: .1
combustion and/or evolution of considerable heat;
.2
evolution of flammable, toxic or asphyxiant gases;
.3
the formation of corrosive substances; or
.4
the formation of unstable substances.
Unless otherwise specified in the Dangerous Goods List, packages containing substances should be hermetically sealed: .1
evolve flammable gases or vapour;
.2
may become explosive if allowed to dry;
.3
evolve toxic gases or vapour;
.4
evolve corrosive gases or vapour; or
.5
may react dangerously with the atmosphere.
Liquids may only be filled into inner packagings which have an appropriate resistance to internal pressure that may be developed under normal conditions of transport. Where pressure may develop in a package by the emission of gas from the contents (as a result of temperature increase or other cause), the packaging may be fitted with a vent, provided that the gas emitted will not cause danger on account of its toxicity, its flammability, the quantity released, etc. The vent should be so designed that, when the packaging is in the attitude in which it is intended to be transported, leakages of liquid and the penetration of foreign matter are prevented under normal conditions of transport. New, remanufactured or re-used packagings, including IBCs and large packagings, or reconditioned packagings and repaired IBCs should be capable of passing the tests prescribed in IMDG code. Before being filled and handed over for transport, every packaging, including IBCs and large packagings, should be inspected to ensure that it is free from corrosion, contamination or other damage and every IBC should be inspected with regard to the proper functioning of any service equipment. Any packaging which shows signs of reduced strength as compared with the approved design type should no longer be used or should be so reconditioned that it is able to withstand the design type tests. Any IBC which shows signs of reduced strength as compared with the tested design type should no longer be used or should be so repaired that it is able to withstand the design type tests.
Empty packagings, including IBCs and large packagings, that have contained a dangerous substance should be treated in the same manner as is required by this Code for a filled packaging, unless adequate measures have been taken to nullify any hazard.
Every packaging, including IBCS, intended to contain liquids should successfully undergo a suitable leak proofness test, and be capable of meeting the appropriate test level indicated in IMDG code for the various types of IBCs: .1
before it is first used for transport;
.2
after remanufacturing or reconditioning of any packaging, before it is re-used for
transport; .3 after the repair of any IBC, before it is re-used for transport. For this test, the packaging, or IBC, need not have its closures fitted. The inner receptacle of a composite packaging or IBC may be tested without the outer packaging, provided the test results are not affected. This test is not necessary for inner packagings of combination packagings or large packagings. Packagings, including IBCS, used for solids which may become liquid at temperatures likely to be encountered during transport should also be capable of containing the substance in the liquid state. Packagings, including IBCS, used for powdery or granular substances should be sift-proof or should be provided with a liner. Explosives, self-reactive substances and organic peroxides Unless specific provision to the contrary is made in this Code, the packagings, including IBCs and large packagings, used for goods of class 1, self-reactive substances of class 4.1 and organic peroxides of class 5.2 should comply with the provisions for the medium danger group (packing group 11).
Use of salvage packagings Damaged, defective or leaking packages or dangerous goods that have spilled or leaked may be transported in special salvage packagings. This does not prevent- the use of a bigger size of packagings of appropriate type and performance level. During transport, packagings, including IBCs and large packagings, should be securely fastened to or contained within the cargo transport unit, so that lateral or longitudinal movement or impact is prevented and adequate external support is provided. Additional general provisions for the use of IBCs When IBCs are used for the transport of liquids with a flashpoint of 61˚C (closed cup) or lower, or of powders liable to dust explosion, measures should be taken to prevent a dangerous electrostatic discharge. For rigid plastics IBCs and composite IBCs with plastics inner receptacles, unless otherwise approved by the competent authority, the period of use permitted for the transport of dangerous liquids should be five years from the date of manufacture of the receptacle except where a shorter period of use is prescribed because of the nature of the liquid to be transported. General provisions concerning packing instructions Packing instructions applicable to dangerous goods of classes 1 to 9 are specified in chapter 4.1. They are subdivided in three sub-sections depending on the type of packagings to which they apply: sub-section 4.1.4.1 for packagings other than IBCs and large packagings: these packing instructions are designated by an alphanumeric code comprising the letter “P”; sub-section 4.1.4.2
for IBCS; these are designated by an alphanumeric code comprising the
letters “IBC”; sub-section 4.1.4.3
for large packagings; these are designated by an alphanumeric code
comprising the letters “LP”. Special packing provisions may also be specified in the packing instruction for individual substances or articles. They are also designated by an alphanumeric code comprising the letters:
“PP”
for packagings other than IBCs and large packagings
“B”
for IBCs
“L”
for large packagings.
Column 8 of the Dangerous Goods List shows for each article or substance the packing instructions) that should be used. Column 9 indicates the special packing provisions applicable to specific substances or articles. Each packing instruction shows, where applicable, the acceptable single and combination packagings. For combination packagings, the acceptable outer packagings, inner packagings and, when applicable, the maximum quantity permitted in each inner or outer packaging are shown. Maximum net mass and maximum capacity are as defined in chapter 1.2.1. Where the packing instructions in this chapter authorize the use of a particular type of outer packaging in a combination packaging (such as 4G), packagings bearing the same packaging identification code followed by the letters “V”, “U” or “W” marked in accordance with the provisions of part 6 (such as “4GV”, “4GU” or “4GW”) may also be used under the same conditions and limitations applicable to the use of that type of outer packaging according to the relevant packing instructions. For example, a combination packaging marked with the packaging code “4GV” may be used whenever a combination packaging marked “4G” is authorized, provided the provisions in the relevant packing instruction regarding types of inner packagings and quantity limitations are respected. The capacity of gas cylinders should not exceed 450 litres. The capacity for gas receptacles should not exceed 1000 litres.
Cargo Handling Equipment
Care and Maintenance of Steel Wire Rope Wire ropes have a lubricant incorporated during manufacture. This serves a dual purpose; it provides corrosion protection and also minimises internal friction. The protection provided by this manufacturing lubricant is normally adequate to prevent deterioration due, to corrosion during the early part of a rope’s life. However, the lubricant applied during manufacture must
be supplemented by lubrication in service. This service lubricant is termed the ‘dressing’ the kind of dressing used and the frequency of application varies with the type of rope and its usage. Details of the maintenance of steel wire rope carried, or fitted in, ships is laid down in the Maintenance Manual of the Company or the Planned Maintenance Schedule (PMS) of the item. Wire hawsers should be stowed on reels under a fitted cover whenever possible. When being reeled in or otherwise stowed, the surface of a wire hawser should be washed with fresh water to free it from salt, then dried with cloths and lightly smeared with the appropriate lubricant. Inspecting Steel Wire Rope
Steel wire ropes carried or fitted in ships must be inspected periodically in accordance with the PMS. When inspecting, the indications described below should be sought: Distortion of Strands: This is the result of damage by kinking, crushing, serious crippling round a bad nip, or other mistreatment. If likely to cause the strands to bear unequal stresses they must be considered as reducing the strength of the rope by 30%; and should they be sufficiently serious to cause the heart to protrude, the rope must be discarded. A crushed rope may be restored to some extent by the careful use of a mallet. Flattening of Some of the Outer Wires by Abrasion: These flat’s are easily seen because the abrasion gives the flattened wires a bright and polished appearance, but they do not affect the strength of the rope unless they are very pronounced. Flats, which extend to threequarters of the diameter of the wires will reduce their cross-sections - and therefore their individual strengths - by 10%, and as only a limited number of wires will be affected the loss in strength of the whole rope will be very small. (These flats must not be confused with flattening of the whole rope, which indicates distortion of the strands and is therefore much more serious). Broken Wires: These are usually the result of fatigue and wear, and mostly occur in crane wires. It is generally accepted that a wire rope is coming to the end of its useful life when one wire of any strand breaks. To deal with a broken wire, grip with a pair of pliers the broken end and bend the wire backwards and forwards until the wire breaks inside the rope between the strands, where it can do no harm. A rope should be discarded if more than 5% of its wires are broken in a length equal to 10 times the diameter of the rope; for example a 24mm diameter, 6X24 wire rope should be discarded if seven broken wires are found in a
length of 240mm. Because of the danger to handlers, berthing wires should be discarded if any broken wires are discovered. Corrosion: Wire rope can be corroded by: The action of damp on the wires from which the gaivanising has worn off, if this occurs to the inner wires first it causes rust to fall out of the rope and is therefore easily detected; The action of fumes and funnel gases, which attack the outside wires, the effect then becomes visible on inspection; Contact with acid, which soaks into the heart and attacks the inside wires; this is not necessarily noticeable on the outside of the rope, and can be the cause of parting without warning. Lack of lubrication is a frequent cause of corrosion. When a wire rope is under tension it stretches and becomes thinner, and during this process the individual wires are compressed and friction is set up; the fibre heart and cores are also compressed, releasing oil to overcome the friction. A wire rope of outwardly good appearance, but with a dry powdery heart or core, has -not been properly maintained and should be treated with caution. Effect of Extreme Cold: When subjected to extreme cold a wire rope may become brittle and lose its flexibility, and an apparently sound rope may part without warning. The brittleness is not permanent and the rope will regain its resilience in a normal temperature, but the potential danger should be remembered when working wires in very cold climates. Testing of Steel Wire Rope The wire from which the rope is to be made is tested before manufacture of the rope to ensure it complies with the relevant Standards with regard to tensile strength, torsion and galvanising properties. After manufacture of each production length of rope, test samples are cut from the finished rope and strand. These samples are used for a tensile test to destruction, tests of preforming of the rope, and tests on a mixture of the individual wires with regard to diameter, tensile strength, torsion and quality of galvanising. Each coil of wire
is accompanied by a certificate of conformity and a test certificate showing the guaranteed minimum breaking strength of the wire. (WHEN NEW.) General Remarks on Steel Wire Rope How to Measure the Size of a Rope The size of a wire rope is the diameter in millimetres of a true circle, which will just enclose all the strands. Measure at each of three places at least 2m apart. The average of these measurements is to be taken as the diameter of the rope. Sheaves for Wire Rope Size of Sheave Required for a Wire Rope Hoist. The diameter of sheave required for each type of six-strand wire rope supplied should be at least twenty times the diameter of the wire. The diameter of a sheave used for any wire rope will considerably affect the life of that rope. As the rope bends round a sheave the strands and wires farthest from the centre of curvature move apart and those nearest the centre of curvature move closer together. This results in the generation of considerable friction between these wires and strands, and the smaller the sheave the greater will be the friction. Friction also increases rapidly with the speed at which the rope is moving. While the rope is bent round a sheave the outer wires are also subjected to a marked additional stress, and the smaller the diameter of the sheave the greater will be the stress. For these reasons the minimum diameters of sheaves recommended from practical experience for various types of ropes at speeds not exceeding 60m per minute are 20 times the diameters of the ropes. For each increase in speed of 30m per minute, 5% must be added to these figures; this will give a rope a reasonable life, but it is emphasized that its life will be greatly increased if still larger sheaves are used. Similarly, if a smaller sheave than that recommended has to be accepted it will shorten the life of the rope, and on no account should a sheave be used that is more than 20% smaller than that determined by reference to the above criteria. Use of Correct Sheave: The life of a rope used for hoisting can also be considerably shortened by using the wrong type of sheave. The groove in the sheave must fit and support the rope as it travels round the sheave, otherwise there will be increased internal friction and external wear. Figure
below shows a sheave with too wide a groove, which results in a flattening of the rope and considerable distortion and internal friction.
Figure below shows a sheave with too narrow a groove, which results in the rope not being supported, the wires of the strands being subjected to considerable wear, and friction being set up between the rope and the sides of the groove.
The groove of the correct sheave should be shaped in cross-section to the true arc of a circle for a distance equal to one-third of the circumference of the rope, and the radius of the groove should be between 5 and 10% greater than the specified radius of the rope.
Cargo Blocks
Rigging of cargo blocks:
Union Purchase – derricks with 2 sets of individual side guys.
Union Purchase – derricks with 1 set of individual side guys and a centre guy.
Rigging for a Gun Tackle: Using one of a set of derricks to load heavy loads, this uses the gynfall wire of the other derrick as a steam (power) guy and also uses the gynfall wire of another derrick as the other steam guy. The derrick head block is connected to a floating block and the gun tackle set up as shown below.
Working with Derricks: While topping/ lowering derricks the following are to be ensured: Both side guys are to be rigged and attended to. As the derrick is being lowered or topped the guys are to be heaved up or slackened. The gynfall wire is to be slackened when topping up the derrick The person attending to the lock should be attentive and at the slightest doubt about the speed or range of topping/ lowering he has to release the lock. So that the derrick is prevented from having a free fall. Lowering of the derrick should be within limits as set out in the derrick rigging plan
While parking the derrick, the control over the side guys should be especially good since with a slight swing the boom is liable to damage other structures. The derricks should not be lowered or topped if the ship is rolling as this would make controlling the derrick very difficult. The end rope of the controlling side guys should be held after a full turn on the rams horn and there should be adequate clear slack. In case of an emergency the next turns should be put on quickly If a ram’s horn is not available then other suitable points may be used, however railing are not to be used. Derricks are secured either on a horizontal crutch (light derricks) or vertically with clamping to the mast. Prior to lowering the derrick the following are to be inspected and if any are found wanting they are to be made good: The crutch post and the bracket at the base are to be inspected The grommet attached to the eye pad (for the gynfall wire) is to be inspected The crutch wood sheathing is to be checked if damaged then a canvas packing may be made in lieu After the derrick is parked, the crutch clamp is to be fitted and the locking arrangement fixed. There should be no play. The side guys are to be tightened and fixed on either side, the extra rope of the guys being neatly coiled onto pallets or slung on railings and tied as a whole – the rope should be covered by a canvas cover The gynfall wire hook is to be hooked to the grommet and the wire tightened (just). The topping wire should not have any weight, but neither should it be slack The heel of the derrick should be covered with canvas and so should be the gynfall and the heel block The preventer wire should be coiled and placed on a pallet Types of Slings in common use:
Beside those mentioned there are various other slings in use. Plate sling: Normally the hinges clamp hangs loose, but once fitted on to the plate and the wire pulled up, the clamps hold the plate very firmly.
Open rope sling: This is used for various types of delicate cargo. Not good for heavy weights.
Canvas sling: Used for lifting small bags of rice and other cereals, the canvas is useful for collecting any spillage that may be caused.
Snotter: This is used for various cargos. It is the most versatile form of sling. Has been used even for container loading, by attaching hook/ shackles to one end and using for such snotters.
Pallet:
This is unitized cargo on a wooden pallet (the bottom double tier of wood). Such cargo may be handles using wore slings but the more safe and common is to use nylon straps or rope slings. If the cargo is loaded on to the ship and the pallet retains the nylon strap then it is termed as pre-slung cargo. The strap is returned to the ship after discharging the cargo.
Hook Handling: Bales are soft cargo and they liable to be damaged by hooks, which penetrate the surface and go deep inside. Bales especially of hessian, bagged cargo and other such cargo are rendered useless if the hooks punch holes into them. Such cargo have a label saying use no hooks. However many port workers use the same hooks to handle these cargo The preferred hooks for such cargoes are shown below. These contain about 3 rows of small raised metal pieces that good at gripping but do not damage the cargo. Some bagged cargo come with ‘ears’ protruding from the four corners of the bags, these ‘ears’ are material of the bag and facilitate the handling of the cargo.
Unitized cargo and Pre-slung cargo Unitized cargo are cargo such as tea or bagged sugar/ asbestos which are placed on top of a wooden pallet and are strapped together into a unit. The advantages of this is that the pallet (now referred to the whole) is easily moved and stored by forklifts. Much manual labour is not required. These types of pallets may be stacked more than one high, though genially 2 high. Ease of lashing and faster loading is the essential advantages. However a lot of broken stowage occurs if the hold dimensions are not square. Thus these type of cargo were unsuitable in old ships which had a tunnel in the after holds and the bilges were rounded. Since these cargo came with their own wooden pallets the dunnaging cost was also saved. After the development of unitized cargo, to speed up further the handling process the cargo pallets were pre-slung with nylon straps. Thus a trailer arriving on the jetty had the pallets neatly arranged and with their own slings. All it took from the shore labour was for a person to hook on the slings. Once on board the slings were not returned but the pallets was stowed with the sling. At the discharging port the forklift brought the pallet top the hatch square and aging the pallet was lifted out with the same sling. On completion of discharge if no cargo was being loaded on the ship the slings were brought back on the ship. The slings were the property of the ship and a strict tally was maintained. The slings were made of nylon straps in various colours and were certified as to the SWL.
With the advent and popularization of containers pre-slung cargo system died out. Unitized cargo is still existent and containers are loaded with unitized cargo. Cranes versus Derricks
Using various cargo gear for handling of cargo. Until the early ‘80’s the primary gear was the derrick. A ship would have a set 0of derricks for each hatch, sometimes if the hatch was big the two sets of derricks. One for the fore part and the other for the after part. The advantages of the derricks is that the boom never moved after it was rigged into position. The only moving parts are the sheaves of the blocks and the wires. As such it was and still is the fastest means of discharging cargo. The advantages of discharging with derricks are: Very few moving parts Time to discharge the least Not much skill required to operate the derricks Breakdown rate low Easy to maintain and to repair on board Spares are easily obtained from even small workshops Spares are cheap The disadvantages are: Cannot discharge large and heavy packages To be effective the derrick plumbing position has to be properly judged. Has to be re-rigged every time the discharge area or loading square changes Requires forklifts to feed the loading area Cranes are used to handle heavy and large packages including grabs on bulk carriers. The advantages of the cranes are: Can discharge from 360˚ angle Can handle cargo from anywhere in the hatch square
Depending on the SWL of the crane can handle very heavy packages Sophisticated and has various safety cut outs to prevent damage and accident. The disadvantages are: Is slow Requires skilled person to operate With unskilled labour requires frequent resetting of the safety cut outs. Maintenance difficult and time consuming The good service provided by a crane is dependent on the maintenance Repairs even more difficult and time consuming Spares are to be ordered in advance from the manufacturer Wires are of special construction and are very expensive. Rigging other derricks: Velle Derrick Rigging
The above is a Velle derrick. This type of derrick is a swinging derrick and is capable of lifting heavy weight and may be found on container-oriented vessels (GC as well as container cargo). The rig is one of the most complicated. On a ship the crew has to be very well experienced to rig up this derrick. The length of the wire is also of special length and may be of 250 – 280 metres. There are 3 winches in operation; the 2 extreme winches have separate barrels, which turn in the opposite direction. The extreme winches share 2 wires, 1 wire starts at 1 winch and ends on the other. The same is for the other wire. The gynfall wire is on a single centre winch. The controls are usually joystick control – 1 for the swinging and the other for the lifting. Thus the extreme winches control the swinging as well as the topping/ lowering action and are controlled by a single control joystick. This is a rare rigging plan and the author has taken great pains to personally draw it out while serving on a ship rigged with 22T Velle derricks. Use of Forklifts: The precautions prior lowering and using forklifts inside the holds: The forklift should not have any oil leakages The height of the hold should be considered while lowering a tall forklift The weight of the forklift together with the cargo should not exceed the load density of the hold The forklift should not be emitting profuse quantities of smoke Adequate fire fighting arrangements should be inside the hold for any fire of the forklift Jute and other flammable cargo should be kept away from any ingress of oil from any leaking forklift The driver should not drive the forklift rashly Adequate lighting should be ensured
Saw dust and sand should be kept stand by for any unforeseen oil leaks.
Cargo Handling Safety Safety while working with cargo gear
Derricks are long hollow steel booms rotating on swivels (heel), they each have a part rope guy and a steel pendant which is used for heaving and positioning the derrick and also to keep the derrick in place. The rope is used in a tackle and can absorb sudden shocks, which come on the derrick while in operation. On the opposite side to the cargo being worked a preventer guy made of wire rope is fitted which is kept slightly slack than the rope guy, This enables the rope guy to stretch before any load comes on the preventer guy. This preventer is the last shock and strain absorber, if the preventer is weak or is damaged it can part with disastrous consequences. So maintaining the preventer and fixing it right is of utmost importance. When the two derricks are used together such that one derrick is positioned just above the loading area on the jetty and the other is positioned above the un loading area within the hold, and the gynfall (load lifting) wires are joined together, the arrangement is called a UNION PURCHASE. This is the fastest method of working cargo, however the loads that this arrangement can lift are less than the individual SWL of the derrick. Additionally there is a risk of the angle subtended at the hook point between the two-gynfall wires going beyond 120degrees when the gynfall wires together act as a pulling force on the derricks laterally and can part the rope guys and or the preventer wire. Thus while the Union Purchase may be the fastest method it requires careful rigging of the derricks as well as experienced winch men to handle the operation together with the duty officer keeping an alert watch on the working of the same.
Cargo blocks are maintained during the voyage, but due to various reasons especially with bush bearings sheaves, the bearing may burn out. Prior breakdown however the block would give an indication by a shrill metallic sound, the crew and duty officer on deck is to be alert on deck and the moment a noise is heard the cargo work is to be stopped and the cause investigated. After each shift of cargo handling – when the stevedores take a break all the cargo gear is to be examined for any wear and tear, if required the defective items are to be replaced. If new blocks are being put to use, they should be greased before fitting them. The test certificates and the cargo-rigging plan should be checked to see that the correct item is being fitted. Often a cargo block breaks down and on examining it is seen that it had a SWL 5T marked on it. Instantly a 5T block is brought from the store and fitted, it could be that the block that had been fitted earlier was of a lesser SWL – so it is always better to check the rigging plan. The handling of the cargo gear also needs to be supervised and any extreme rough handling should be stopped. Where the gyn fall wire rubs against the hatch coaming or gunwale suitable padding should be place.
The derricks should be properly rigged and the preventer wire should, if it has been rigged properly, stretch when the load is in between the two derricks (in case of union purchase). With no load the preventer should be with some slack. The cargo hook should have a locking clip to prevent the sling from slipping out of the hook. Cargo handling areas should be cordoned off so that no person is found walking or standing under a cargo load. Free passage may be used of the non-working side of the cargo hatch. A helmet is no safety for a load if it falls – helmets are satisfactory if some loose small objects fall. For heavy individual loads a swinging derrick is often used either a single derrick is used where the guy ropes are removed and other winch wires (also called steam guys) are used to control the movement of the derrick. A number of other types of rigging have over the years been tried out some with great success and some with little. Jumbo derricks were derricks attached to a Mast and could lift as the name suggests heavy loads, the forward Jumbo derrick was generally for extra heavy loads while the aft derrick was for slightly lesser loads. In preparing for operation the Jumbo derricks required four winches – 1 for topping the derrick, one for lifting the load and two for swinging the derrick. As such prior using the Jumbo derrick was rigged and the lashings were then removed. The rigging entailed that four light derricks were inoperable since their winches were requisitioned, so efficient planning on the part of the chief officer was required. Stulken derricks had a single boom but the rigging was such that a single operator could control the movement of the derrick, another advantage was that these derricks could service two adjacent holds by being capable of being plumbed for either hold. Velle derricks (with Thomson rig) were also very popular for ships, which often loaded heavy loads such as containers; in this the control again was unified into a single man operation. The above derricks were however very difficult to rig if the wire had to be changed, and often the crew would spend an entire day rigging one derrick. Cargo cranes are used on many ships and especially on bulk cargo carriers. These may be light cranes for general cargo ships or heavy-duty cranes for lifting huge grabs or containers.
Ships, which have slots for containers but also load general cargo, are often fitted with cranes with SWL up to 40 tonnes. If a single crane is incapable of being used to lift such heavy containers then two cranes are ‘twinned’ to handle the load. The control is unified and both the cranes work in tandem. Hatch Covers
Hatch covers especially the Macgregor rolling hath covers should be opened by a responsible person and after opening the hatch covers should be locked to prevent their rolling and closing on their own due to excessive trim. Partially opening of hatch covers should be avoided unless there is a means of locking them into place. Prior opening a hatch cover the eccentric wheels should be examined to see whether any have not been made upright for opening. All loose gear on top of the hatch cover should be removed. Under no circumstances should a hatch cover be opened with a load on it. Also the hatch cover recess should be physically checked to see that not obstruction is present and that no stevedore is napping in the recess. Similarly a hatch cover should not be closed with load on it and any deck cargo loaded onto hatch cover should be done only after the hatch cover has be battened down (eccentric wheels turned down, cleats and wedges locked. Prior closing it should also be ensured that the track way is clear of all ropes, portable light wires and any other obstruction and that the locking has been removed. Tween deck hatch covers once they are opened are to be fenced off, generally stanchions (Height – 1.2m) are provided which have to be rigged and the wire/ chains fitted. Nobody is to be allowed to work unless these are rigged. Cargo Lighting Portable lights are required to be rigged in holds where there is no provision for fixed lighting system. These lights are commonly called cargo cluster lights and have 4 or more light bulbs fixed to a common pan shaped metal holder. A wire mesh covers the front of the ‘pan’ and the inside of the ‘pan’ is painted white to reflect the light.
The light is attached to a short length of small dia rope to facilitate its being fixed at the coaming. The lights are to be checked in the afternoon and should be rigged and in place by sunset. The lights should be switched when there is adequate light in the hold in the morning and should be un-rigged and stored neatly. They should be switched on only after the gangs come for the work and should be promptly switched off once all have left the hold. Often the cargo lights are not removed and the hatch covers are closed especially when closing due to rain. This is fraught with danger, for the lead is cut and the cluster light falls into the hold, the bulbs are hot and may cause a fire, also the cut lead has power in it and may cause a short circuit for the system or may electrocute any person close by. An experienced crew should supervise the rigging of cargo lights since if loading jute or other flammable cargo the distance off from the cargo should be maintained. Also the shore people may tend to drag a light inside the hold to facilitate loading, this should be supervised. The electric cord should never lift the lights rather the ropes attached for the same should be used. In holds where fixed lighting is available the light fittings should be inspected prior switching on and then only the lights are to be switched on. Water seepage especially during rain may cause short circuits and may eventually lead to fires. All lights should be switched off when no longer required.
Oil Tanker
A tanker is a specialized ship intended for the carriage of bulk liquid cargo. An Oil tanker again is further divided into 2 basic types, namely Crude Oil Tanker and Product Oil Tanker. For both of the above the cargo of oil is carried within the tanks similar to the holds of other ships, the difference being that the bulkheads are extra strengthened to take in the load, and the hatch or rather the tank openings are very small, the sole purpose of having them is for Man Entry and for small repair work in the dry docks. The cargo of oil is loaded on to the ships tanks by pipelines, which are fixed on the ship (permanent structure), the shore pipelines are connected to the ships pipelines at the manifold on either side of the ship. Note that some special ships also have manifolds at the bow and at the stern. The shore pipelines may be connected using flexible steel rimmed rubber hoses (small ports/ Ship to ship transfers/ SBM) – the flexible come in small lengths are connected to each other to make them long pieces. The shore pipelines may also be connected with rigid loading arms – also called ‘chiksons’, which are remotely controlled and take in the roll of the ship to a certain extent but the fore and aft movement of the ship has to be kept to a minimum. The combined pipeline system of the shore and the ship deliver the oil to the cargo oil tanks directly via the drop lines. These are as the name suggests pipelines, which drop to the bottom of the tanks vertically from the pipeline on deck – thus bypassing the pump room. There are various cross- over valves, which are opened in order to load a group of tanks.
The shore system starts to pump/ delivers by gravity (some Persian Gulf ports) at a slow rate, so that any leakages can be detected and to check whether the right tank is receiving the oil or not, once the shore and the shipside are satisfied the pumping – loading of the cargo is increased. In case of any subsequent leakages that are detected the ship valves should not be shut abruptly, rather the shore has to be informed first and then only the ship valves are to shut, this to prevent pressure surge from bursting the pipelines. To prevent this surge from affecting the pipelines the cargo valves have set times at which they close – this depends on the size of the valves – typically a 550mm valve would shut at about 24 seconds, whereas a 250mm valve would shut at 6-8 seconds. After the ship completes her loading the stage is set for the unloading or discharging operation. While loading the cargo had by passed the pump room, now however the cargo from the tanks is allowed to flow to the pump room through the bottom pipelines. Just within the pumproom and at the pumproom bulkhead are situated isolation valves known as ‘Bulkhead Master valves’, by opening the valves the oil is led to the pump suction valve and on opening that the oil flows to the centrifugal pumps. Turbines, which are situated in the Engine Room, commonly drive these pumps; the shaft penetrates the ER bulkhead and drives the pump situated at the bottom of the pumproom. The pump accelerates the flow of the oil into the discharge pipeline and this oil is thus led on the deck pipelines and to the manifold from where it flow through the flexible pipeline or the hard loading arm to the shore pipeline system. The Pump Room
This is a cofferdam kind of space – in fact it is accepted as a cofferdam, which begins on main deck and ends at the keel. It may have more than 2 decks, however these decks are not normally solid decks but are partial decks made of expanded metal, so you are able to see right to the bottom. There would be a companionway leading from the top to the next deck and so on right to the bottom.
At the lowermost deck are situated the Cargo Oil Pumps (COP’s). The numbers of pumps vary in number – for crude oil tankers it is normal to have 4 pumps, three being used at any one time. For product oil tankers the number of pumps depend on the number of grade of oil that the ship is capable of carrying. So if the ship can carry 4 grades of oil then she would be having 4 pumps. Once the gravity flow to the COP’s is not possible the stripped pumps are started, these pumps are of the reciprocating type and have great capacity to create partial vacuum to suck out the remaining oil from the tanks. Again on a product oil tanker the number of stripped pumps would be equal to the number of grades of oil that it can carry. Earlier on Crude oil carrier there would be stripper pumps of the reciprocating type however today largely eductors are used to remove the remaining oil from the tank. Generally 2 eductors are provided on each crude oil tanker. However 1 stripper pump is always provided to strip the cargo lines of any residual oil and to pump the same to the shore system. The pumproom is a hazardous area as such the light fittings are gas tight and only tanker safety torches are used. The ventilation system is of the exhaust type and has intakes from all the levels with the intakes being fitted with closing devices so that if required only a certain level can be evacuated. Hydrocarbon gases being heavier than air tend to settle at the bottom of the pumproom as such the main exhaust are always from the bottom level. The pumproom lighting is devised in such a way that the lights do not come on unless the ventilation has been started and is kept on for 15 minutes. AT the top of the pumproom a harness and lifting arrangement is provided to lift out a person from the lowermost deck, for this reason a clear passage is left vertically from the top to the bottom of the pumproom. Fire man’s outfit are also placed at the top of the pumproom, the pumproom may have different types of fixed fire fighting appliances such as total flooding by CO2 or by foam applicators fitted in the bilges (below the floor plates under the lowermost deck).
Bilge alarms are fitted which give alarms when the bilges are filled – a high level and a low level alarm is fitted which gives indications in the Engine room as well as in the Cargo Control room.
Picture shows the main deck layout of a Product tanker (capable of carrying 4 grades of oil):
The same tanker – with the tank layout.
And part of the pump room layout of the same tanker.
The above shows the location of the drop valves; drop lines, line master, bulkhead master and the bottom lines.
Cargo Oil Pumps (COP) A centrifugal pump, in the pumproom bottom platform. The dark green pipeline is the discharge line. The pump consists of an impeller which rotates within the casing. Due to this rotation which is generally about 1000 – 1700 rpm the oil is speeded up and this increase in velocity causes the oil to flow out at a great pressure. These pumps are capable of delivering a very high rate of discharge (up to 4000 m3/hr). With this type of pump the level of oil has to be above the pump – as such the pump is situated at the bottom of the pump room.
Another detail of the same centrifugal pump.
The earlier centrifugal pump situated in the pumproom is driven by a shaft which is connected to the steam turbine – situated in the ER. The shaft passes from the ER to the pumproom through the pumproom bulkhead via a gas and oil tight gasket.
The turbines are driven by superheated steam from the boiler in the ER. Positive displacement pumps such as the reciprocating pump work on the principle of a hand pump – the movement of the piston creates a vacuum which sucks out the fluid. However the size of the pump is dependent on the size of the piston and the length of the strokes so for discharging at a high rate is practically impossible. In general these pumps are used to discharge small quantities of oil such as the strippings – the balance that the centrifugal pump cannot discharge due to the oil going below the level of the pump. The pump is used today on crude tankers to strip out the pipelines after discharging and then collecting these line content (small) and then pumping them to shore.
Eductors Eductors work on the principles of Bernoulli’s Principle. A driving fluid is pumped down the main line, with very high velocity, through a constriction, and past a relatively smaller opening, thus creating a vacuum. When eductors are used for clean ballast, the driving fluid is seawater. When used for stripping crude oil, the driving fluid is the cargo itself- delivered by means of a bypass from one of the main cargo pumps. When used for stripping tank washings, the driving fluid is from the secondary slop tank and then re-circulated back to the primary slop tank. In the latter case the driving fluid is either crude oil or seawater, depending on the tank cleaning method. Eductors are simple and rugged, have no moving parts, and do not become air locked like other type of pumps. They are widely used on tankers of all types and sizes.
Tank layout of a crude oil tanker:
The Pipeline system: Pipeline systems on tankers differ in their degree of sophistication, depending on employment of the tanker. ULCC’s and VLCC’s have relatively simple pipeline systems usually the direct line system. Some product (parcel) tankers may have very sophisticated piping systems. This could be the ring main system or in case of a chemical product tanker it could mean an individual pipeline and an individual pump for every tank on board. Basically there are three systems of pipelines found on tankers, and the fourth system being the free flow system found on large crude carriers Ring Main System Direct line system Single line to Single tank system (Chemical/Product ship) Free Flow system
Ring Main System:
It is generally of a square or circular layout. It is used mostly on product tankers, as segregation of cargo is required. Though the system is expensive, as more piping, and extra number valves are used. However if the vessel is carrying many grades of cargo, the advantages compensate for the extra cost of the original outlay.
Direct Line System:
This system is mainly found on crude oil carriers where up to 3 grades of cargo can be carried as most of the direct pipeline systems is fitted with three direct lines. This system is cheaper to construct. The disadvantages over the ring main system, is that line washing is more difficult, the system has fewer valves which make pipeline leaks difficult to control, as the system lacks versatility there is problem with line and valve segregation. This system provides the vessel to carry as many grades as there are tanks. The disadvantage is the cost factor having a multitude of pumps on board.
Free flow Tanker: This system is usually found on large crude carriers, where the cargo piping is not used for the discharge of cargo. Instead, gate valves are provided on the bulkheads of the tanks which when opened; allow the oil to flow freely in the aft most tank and into the COP. The advantages of this system are primarily the cost factor, it allows for fast drainage and efficient means of pumping the cargo tanks. Disadvantages are of single crude being shipped. Independent System: This layout is not very common in the tanker trade. This system is quite normal on chemical ships. There are some Product Tankers that have this system fitted on the ships. This is a single line servicing an individual tank through an independent pump that could be either a submersible pump or a deep well pump. Enclosed Space Entry An enclosed space is one with restricted access that is not subject to continuous ventilation and in which the atmosphere may be hazardous due to the presence of hydrocarbon gas, toxic gases, inert gas or oxygen deficiency. This definition includes cargo tanks, ballast tanks, fuel tanks, water tanks, lubricating oil tanks, slop and waste oil tanks, sewage tanks, cofferdams, duct keels, void spaces and trunkings, pipelines or fittings connected to any of these. It also includes inert gas scrubbers and water seals and any other item of machinery or equipment that is not routinely ventilated and entered, such as boilers and main engine crankcases. Many of the fatalities in enclosed spaces on oil tankers have resulted from entering the space without proper supervision or adherence to agreed procedures. In almost every case the fatality would have been avoided if the simple guidance in this chapter had been followed. The rapid rescue of personnel who have collapsed in an enclosed space presents particular risk. It is a human reaction to go to the aid of a colleague in difficulties, but far too
many additional and unnecessary deaths have occurred from impulsive and ill-prepared rescue attempts. Respiratory hazards from a number of sources could be present in an enclosed space. These could include one or more of the following: Respiratory contaminants associated with organic vapours including those from aromatic hydrocarbons, benzene, toluene, etc.; gases such as hydrogen sulphide; residues from inert gas and particulates such as those from asbestos, welding operations and paint mists. Oxygen deficiency caused by, for example, oxidation (rusting) of bare steel surfaces, the presence of inert gas or microbial activity. Hydrocarbon Vapours
During the carriage and after the discharge of hydrocarbons, the presence of hydrocarbon vapour should always be suspected in enclosed spaces for the following reasons: Cargo may have leaked into compartments, including pumprooms, cofferdams, permanent ballast tanks and tanks adjacent to those that have carried cargo. Cargo residues may remain on the internal surfaces of tanks, even after cleaning and ventilation. Sludge and scale in a tank which has been declared gas free may give off further hydrocarbon vapour if disturbed or subjected to a rise in temperature. Residues may remain in cargo or ballast pipelines and pumps. The presence of gas should also be suspected in empty tanks or compartments if nonvolatile cargoes have been loaded into non-gas free tanks or if there is a common ventilation system which could allow the free passage of vapours from one tank to another.
Oxygen Deficiency Lack of oxygen should always be suspected in all enclosed spaces, particularly if they have contained water, have been subjected to damp or humid conditions, have contained inert gas or are adjacent to, or connected with, other inerted tanks. Other Atmospheric Hazards These include toxic contaminants such as benzene or hydrogen sulphide, which could remain in the space as residues from previous cargoes. ATMOSPHERE TESTS PRIOR TO ENTRY General Any decision to enter an enclosed space should only be taken after the atmosphere within the space has been comprehensively tested from outside the space with test equipment that has recently been calibrated and checked for correct operation. It is essential that all atmosphere testing equipment used is: Suitable for the test required; Of an approved type; Correctly maintained; Frequently checked against standard samples. A record should be kept of all maintenance work and calibration tests carried out and of the period of their validity. Testing should only be carried out by personnel who have been trained in the use of the equipment and who are competent to interpret the results correctly. Care should be taken to obtain a representative cross-section of the compartment by sampling at several depths and through as many deck openings as practicable. When tests are being carried out from deck level, ventilation should be stopped and a minimum period of about 10 minutes should be allowed to elapse before readings are taken. Even when tests have shown a tank or compartment to be safe for entry, pockets of gas should always be suspected. Hence, when descending to the lower part of a tank or compartment, further atmosphere tests should be made. Regeneration of hydrocarbon gas
should always be considered possible, even after loose scale has been removed. The use of personal detectors capable of continuously monitoring the oxygen content of the atmosphere, the presence of hydrocarbon vapour and, if appropriate, toxic vapour is strongly recommended. These instruments will detect any deterioration in the quality of the atmosphere and can provide an audible alarm to warn of the change in conditions. While personnel remain in a tank or compartment, ventilation should be continuous and frequent atmosphere tests should be undertaken. In particular, tests should always be made before each daily commencement of work or after any interruption or break in the work. Sufficient samples should be drawn to ensure that the resulting readings are representative of the condition of the entire space. Hydrocarbon Vapours
To be considered safe for entry, whether for inspection, cold work or hot work, a reading of not more than 1% LFL must be obtained on suitable monitoring equipment. Benzene
Checks for benzene vapour should be made prior to entering any compartment in which a cargo that may have contained benzene has recently been carried. Entry should not be permitted without appropriate personal protective equipment if statutory or recommended Permissible Exposure Limits (PEL’s) are likely to be exceeded. Tests for benzene vapours can only be undertaken using appropriate detector equipment, such as that utilizing detector tubes. (Benzene causes cancer, and has a delayed action which may be up to 20years) Detector equipment should be provided on board all vessels likely to carry cargoes in which benzene may be present.
Hydrogen Sulphide Although a tank which has contained sour crude or sour products will contain hydrogen sulphide, general practice and experience indicates that, if the tank is thoroughly washed, the hydrogen sulphide should be eliminated. However, the atmosphere should be checked for hydrogen sulphide content prior to entry and entry should be prohibited in the event of any hydrogen sulphide being detected. Hydrogen sulphide may also be encountered in pumprooms and appropriate precautions should therefore be taken. Oxygen Deficiency
Before initial entry is allowed into any enclosed space, which is not in daily use, the atmosphere should be tested with an oxygen analyzer to check that the normal oxygen level in air of 21% by volume is present. This is of particular importance when considering entry into any space, tank or compartment that has previously been inerted. Generally nearly all substances have been assigned Permissible Exposure Limits (PEL) and /or Threshold Limit Values (TLVs). The term Threshold Limit Value (TLV) is often expressed as a time weighted Average (TWA). The use of the term Permissible Exposure Limit refers to the maximum exposure to a toxic substance that is allowed by an appropriate regulatory body. The PEL is usually expressed as a Time Weighted Average, normally averaged over an eighthour period. Short Term Exposure Limit (STEL), is normally expressed as a maximum airborne concentration averaged over a 15-minute period. The values are expressed as parts per million (PPM) by volume of gas in air. Toxicity can be greatly influenced by the presence of some minor components such as aromatic hydrocarbons (e.g. benzene) and hydrogen sulphide. A TLV of 300PPM, corresponding to about 2%LEL, is established for gasoline vapours.
Entry Procedures
General A responsible officer prior to personnel entering an enclosed space should issue an entry permit. An example of an Enclosed Space Entry Permit is provided in ISGOTT. Suitable notices should be prominently displayed to inform personnel of the precautions to be taken when entering tanks or other enclosed spaces and of any restrictions placed upon the work permitted therein. The entry permit should be rendered invalid if ventilation of the space stops or if any of the conditions noted in the checklist change. No one should enter any cargo tank, cofferdam, double bottom or other enclosed space unless an entry permit has been issued by a responsible officer who has ascertained immediately before entry that the atmosphere within the space is in all respects safe for entry. Before issuing an entry permit, the responsible officer should ensure that: The appropriate atmosphere checks have been carried out, namely oxygen content is 21% by volume, hydrocarbon vapour concentration is not more than 1% LFL and no toxic or other contaminants are present. Effective ventilation will be maintained continuously while the enclosed space is occupied. Lifelines and harnesses are ready for immediate use at the entrance to the space. Approved positive pressure breathing apparatus and resuscitation equipment are ready for use at the entrance to the space. Where possible, a separate means of access is available for use as an alternative means of escape in an emergency. A responsible member of the crew is in constant attendance outside the enclosed space in the immediate vicinity of the entrance and in direct contact with a responsible officer. The lines of communications for dealing with emergencies should be clearly established and understood by all concerned. In the event of an emergency, under no circumstances should the attending crew member enter the tank before help has arrived and the situation has been evaluated to ensure the safety of those entering the tank to undertake rescue operations.
Regular atmosphere checks should be carried out all the time personnel are within the space and a full range of tests should be undertaken prior to re-entry into the tank after any break. The use of personal detectors and carriage of emergency escape breathing apparatus are recommended. Reference should be made to ISGOTT for additional guidance on entry into pumprooms.
Cargo Measurement
Tank quantities are measured by noting the level of the fluid in the tank and then referring to the tank calibration tables and noting down the quantity specified against that level. Thus we take the sounding of a tank – water and fuel on all type of ships and then follow the above practice. Note that prior to referring to the tables the tank level has to be corrected for error due to trim and list. These corrections are generally given in the tank calibration tables. The above method though fine by all are turned upside down on a tanker. A tanker loads oil and it is not feasible to take a sounding every now and then – besides it is very messy. On tankers therefore instead of sounding the reverse is measured – that is the vacant level to reach the top of the tank – or the ullage. Thus ullage tables are nothing but the sounding table reversed. Note the following:
The maximum sounding of a tank is 24.35m the maximum ullage is also 24.35m. When the sounding is 10m the ullage would be 24.35 – 10 = 14.35m Thus when a tank is filling up the sounding increases, whereas the ullage reduces. Once the liquid level is obtained the same is seen for the quantity (Volume) in the calibration book. This is the Gross volume at Natural Temperature GVn (observed temperature being taken of the liquid at three levels and then averaged) The sounding of any water which may be present in the tanks is now taken (some water is usually present in crude oil and also sometimes in product oil). The calibration tables are again referred and the volume of Free Water is obtained. Thus the Net Volume at Natural (NVn) is found by subtracting the water form the GVn. This NVn is now converted to a volume at 15˚C by looking up the correction in the ASTM tables – a factor is found, which converts the Volume at Natural temperature to a volume at 15˚C. This would then be the Net volume of oil loaded. The conversion is required since the loading temperature may be 40˚C whereas the temperature of the oil after a voyage of 30 days would drop to about 30˚C or so. Obviously the volume would then contract, so a standard temperature correction is done to 15˚C at both the load as well as the disport. For weight calculations the volume at 15˚C is taken and this is multiplied by the density at 15˚C of the oil (actually a factor which is 0.0011 less than the density at 15˚C is used)
Bale Capacity: This is the cubic capacity of a space when the breadth is taken from the inside of the cargo battens, the depth from the wooden ceiling to the underside of the deck beams and the length from the inside of the bulkhead stiffeners or sparring where fitted. Grain Capacity: This is the cubic capacity of a space when the lengths, breadths and the depths are taken right to the ships side plating. An allowance is usually made for the volume occupied by frames and beams. Stowage Factor: This is the volume occupied by unit weight of cargo. Usually expressed as cubic metres/ tonne. It does not take into account space, which may be lost due to broken stowage. However it obtained by multiplying the greatest length by the greatest breadth with the greatest height.
Example: A bale of Hessian has the following dimensions: L – 1.2 M, B – 1.2 M and H – 1.5 M. The bale weighs 800 KGS. The SF then would be obtained by: Volume: L x B x H = 1.2 x 1.2 x 1.5 = 2.16 CBM So, 2.16 CBM would weigh 0.8 MT Or 1 MT of the cargo in bales would occupy 2.7 CBM
Broken Stowage: The space between packages which remains unutilized. This is generally expressed as a percentage and the amount that is to be allowed varies with differ rent cargo and the shape of the hold. It is greatest when large cases have to be loaded in a n end hold, where the after end narrows down considerably. BS is generally not given in any of the booking lists, but is a ship/ hold experience factor or a sister ship experience factor for that particular cargo. The most commonly accepted figure is about 10%, thus with a BS of 10% the available cargo space that may be loaded would be 90%. Example: Given to load a quantity of light packaged cargo having a SF at 2.7 CBM/MT, the hold space (bale capacity) is given as 885 CBM. To find the amount of cargo that may be loaded in the hold. The bale capacity is 885 CBM but since the BS is 10% the available space would be 885 x 90% Or 796.5 CBM Thus the cargo that can be loaded would be 796.5/ 2.7 = 295 MT (about). However this BS that is given is for a proper stow as per earlier estimates, the final stow should also be a good stow or the BS that would be obtained on final completion would vary. Thus on final completion of loading if the ‘tween deck was loaded with only 275 MT then the BS that was obtained would be: Full capacity 885 CBM at 2.7 CBM/ MT could take in 885/ 2.7 = 328 MT But it finally took in only 275 MT thus had a shortfall was 53 MT which was due to BS. Thus,
328 MT – 275 MT = 53 And 53 / 328 = 0.16 Expressed as a percentage = 16% was lost due to BS instead of the earlier estimated figure of 10%. Example-101 Given to load No. 1 Lower Hold Bale capacity – 962 m3 Max Height – 11.945m Permissible Load – 9.2 t/ m2 Forward Breadth – 4.5m After Breadth – 11.5m Mean Breadth – 8m Length – 10.5m
Area of the hold – Length x Mean Breadth A = 11 x 8 = 88m2 Permissible Load density – 9.2 t/m2 Therefore the load if evenly spread all over the hold would enable the hold to be loaded with: 88 x 9.2 = 809.6 MT Example-102 Given to load No. 1 Lower Hold Bale capacity – 962 m3 Max Height – 11.945m Permissible Load – 9.2 t/ m2 Forward Breadth – 4.5m After Breadth – 11.5m
Mean Breadth – 8m Length – 10.5m Cargo – SF 2.7 m3/t Volume – 962 m3 Cargo can load – Volume/ SF Cargo to load – 962/ 2.7 Cargo to load – 356 MT
Example-103 Given to load No. 1 Lower Hold Bale capacity – 962 m3 Max Height – 11.945m Permissible Load – 9.2 t/ m2 Forward Breadth – 4.5m After Breadth – 11.5m Mean Breadth – 8m Length – 10.5m Cargo – 150 MT, SF 2.7 m3/t to load only in after half of the hatch space After breadth – 11.5m Mid Breadth – 8m Mean breadth – 9.75m ½ Length – 5.25m Area of ½ hold as above – 51.2 m2 Volume of above – 611 m3 Max permissible load on 51.2 m2 – 9.2 x 51.2 = 471 MT Since the cargo has a SF of 2.7 m3/t the volume occupied by the cargo would be:
Volume/ SF 611/ 2.7 = 226 MT So the after half of the hold would take in 226 MT of the cargo and would remain within the permissible load density. Let us now fill up the forward half of the hold with a cargo having a SF of 0.8 m3/t (heavy cargo) Cargo – ?? MT, SF 0.8 m3/t to load in forward half of the hatch space After breadth – 4.5m Mid Breadth – 8m Mean breadth – 6.25m ½ Length – 5.25m Area of ½ hold as above – 32.8 m2 Volume of above – 392 m3 Permissible load would be: 32.8 m2 x 9.2 (SF) = 302 MT Cargo that could be loaded as per SF – Volume/ SF = 392/ 0.8 = 490 MT But the permissible load is – 302 MT, so the cargo could not be loaded right up to the top of the hold. So there would be a height restriction. First we find the Volume as required for the permissible load of 302 MT Load 302 = Volume/ 0.8 Or Volume = 302 x 0.8 = 242 m3 Since we know the area as 32.8 m2 we can find the height, Volume/ Area or 242/ 32.8 = 7.4 m Thus the cargo of 302 MT could be loaded only up to a height of 7.4m.
Enclosed Space Entry An enclosed space is one with restricted access that is not subject to continuous ventilation and in which the atmosphere may be hazardous due to the presence of hydrocarbon gas, toxic gases, inert gas or oxygen deficiency. This definition includes cargo tanks, ballast tanks, fuel
tanks, water tanks, lubricating oil tanks, slop and waste oil tanks, sewage tanks, cofferdams, duct keels, void spaces and trunkings, pipelines or fittings connected to any of these. It also includes inert gas scrubbers and water seals and any other item of machinery or equipment that is not routinely ventilated and entered, such as boilers and main engine crankcases. Many of the fatalities in enclosed spaces on oil tankers have resulted from entering the space without proper supervision or adherence to agreed procedures. In almost every case the fatality would have been avoided if the simple guidance in this chapter had been followed. The rapid rescue of personnel who have collapsed in an enclosed space presents particular risk. It is a human reaction to go to the aid of a colleague in difficulties, but far too many additional and unnecessary deaths have occurred from impulsive and ill-prepared rescue attempts. Respiratory hazards from a number of sources could be present in an enclosed space. These could include one or more of the following: Respiratory contaminants associated with organic vapours including those from aromatic hydrocarbons, benzene, toluene, etc.; gases such as hydrogen sulphide; residues from inert gas and particulates such as those from asbestos, welding operations and paint mists. Oxygen deficiency caused by, for example, oxidation (rusting) of bare steel surfaces, the presence of inert gas or microbial activity. Hydrocarbon Vapours During the carriage and after the discharge of hydrocarbons, the presence of hydrocarbon vapour should always be suspected in enclosed spaces for the following reasons: Cargo may have leaked into compartments, including pumprooms, cofferdams, permanent ballast tanks and tanks adjacent to those that have carried cargo. Cargo residues may remain on the internal surfaces of tanks, even after cleaning and ventilation. Sludge and scale in a tank which has been declared gas free may give off further hydrocarbon vapour if disturbed or subjected to a rise in temperature. Residues may remain in cargo or ballast pipelines and pumps.
The presence of gas should also be suspected in empty tanks or compartments if non-volatile cargoes have been loaded into non-gas free tanks or if there is a common ventilation system which could allow the free passage of vapours from one tank to another. Oxygen Deficiency Lack of oxygen should always be suspected in all enclosed spaces, particularly if they have contained water, have been subjected to damp or humid conditions, have contained inert gas or are adjacent to, or connected with, other inerted tanks. Other Atmospheric Hazards These include toxic contaminants such as benzene or hydrogen sulphide, which could remain in the space as residues from previous cargoes. ATMOSPHERE TESTS PRIOR TO ENTRY General Any decision to enter an enclosed space should only be taken after the atmosphere within the space has been comprehensively tested from outside the space with test equipment that has recently been calibrated and checked for correct operation. It is essential that all atmosphere testing equipment used is: Suitable for the test required; Of an approved type; Correctly maintained; Frequently checked against standard samples. A record should be kept of all maintenance work and calibration tests carried out and of the period of their validity. Testing should only be carried out by personnel who have been trained in the use of the equipment and who are competent to interpret the results correctly. Care should be taken to obtain a representative cross-section of the compartment by sampling at several depths and through as many deck openings as practicable. When tests are being carried out from deck level, ventilation should be stopped and a minimum period of about 10 minutes should be allowed to elapse before readings are taken. Even when tests have shown a tank or compartment to be safe for entry, pockets of gas should always be suspected. Hence, when descending to the lower part of a tank or compartment,
further atmosphere tests should be made. Regeneration of hydrocarbon gas should always be considered possible, even after loose scale has been removed. The use of personal detectors capable of continuously monitoring the oxygen content of the atmosphere, the presence of hydrocarbon vapour and, if appropriate, toxic vapour is strongly recommended. These instruments will detect any deterioration in the quality of the atmosphere and can provide an audible alarm to warn of the change in conditions. While personnel remain in a tank or compartment, ventilation should be continuous and frequent atmosphere tests should be undertaken. In particular, tests should always be made before each daily commencement of work or after any interruption or break in the work. Sufficient samples should be drawn to ensure that the resulting readings are representative of the condition of the entire space.
Hydrocarbon Vapours To be considered safe for entry, whether for inspection, cold work or hot work, a reading of not more than 1% LFL must be obtained on suitable monitoring equipment. Benzene Checks for benzene vapour should be made prior to entering any compartment in which a cargo that may have contained benzene has recently been carried. Entry should not be permitted without appropriate personal protective equipment if statutory or recommended Permissible Exposure Limits (PEL’s) are likely to be exceeded. Tests for benzene vapours can only be undertaken using appropriate detector equipment, such as that utilizing detector tubes. Detector equipment should be provided on board all vessels likely to carry cargoes in which benzene may be present. Hydrogen Sulphide Although a tank which has contained sour crude or sour products will contain hydrogen sulphide, general practice and experience indicates that, if the tank is thoroughly washed, the hydrogen sulphide should be eliminated. However, the atmosphere should be checked for hydrogen sulphide content prior to entry and entry should be prohibited in the event of any hydrogen sulphide being detected. Hydrogen sulphide may also be encountered in pumprooms and appropriate precautions should therefore be taken. Oxygen Deficiency Before initial entry is allowed into any enclosed space, which is not in daily use, the atmosphere should be tested with an oxygen analyzer to check that the normal oxygen level in air of 21% by volume is present. This is of particular importance when considering entry into any space, tank or compartment that has previously been inerted. Generally nearly all substances have been assigned Permissible Exposure Limits (PEL) and /or Threshold Limit Values (TLVs). The term Threshold Limit Value (TLV) is often expressed as a time weighted Average (TWA). The use of the term Permissible Exposure Limit refers to the maximum exposure to a toxic substance that is allowed by an appropriate regulatory body. The PEL is usually expressed as a Time Weighted Average, normally averaged over an eighthour period.
Short Term Exposure Limit (STEL), is normally expressed as a maximum airborne concentration averaged over a 15-minute period. The values are expressed as parts per million (PPM) by volume of gas in air. Toxicity can be greatly influenced by the presence of some minor components such as aromatic hydrocarbons (e.g. benzene) and hydrogen sulphide. A TLV of 300PPM, corresponding to about 2%LEL, is established for gasoline vapours. Entry Procedures General An entry permit should be issued by a responsible officer prior to personnel entering an enclosed space. An example of an Enclosed Space Entry Permit is provided in ISGOTT. Suitable notices should be prominently displayed to inform personnel of the precautions to be taken when entering tanks or other enclosed spaces and of any restrictions placed upon the work permitted therein. The entry permit should be rendered invalid if ventilation of the space stops or if any of the conditions noted in the checklist change. No one should enter any cargo tank, cofferdam, double bottom or other enclosed space unless an entry permit has been issued by a responsible officer who has ascertained immediately before entry that the atmosphere within the space is in all respects safe for entry. Before issuing an entry permit, the responsible officer should ensure that: The appropriate atmosphere checks have been carried out, namely oxygen content is 21% by volume, hydrocarbon vapour concentration is not more than 1% LFL and no toxic or other contaminants are present. Effective ventilation will be maintained continuously while the enclosed space is occupied. Lifelines and harnesses are ready for immediate use at the entrance to the space. Approved positive pressure breathing apparatus and resuscitation equipment are ready for use at the entrance to the space. Where possible, a separate means of access is available for use as an alternative means of escape in an emergency. A responsible member of the crew is in constant attendance outside the enclosed space in the immediate vicinity of the entrance and in direct contact with a responsible officer. The lines
of communications for dealing with emergencies should be clearly established and understood by all concerned. In the event of an emergency, under no circumstances should the attending crew member enter the tank before help has arrived and the situation has been evaluated to ensure the safety of those entering the tank to undertake rescue operations. Regular atmosphere checks should be carried out all the time personnel are within the space and a full range of tests should be undertaken prior to re-entry into the tank after any break. The use of personal detectors and carriage of emergency escape breathing apparatus are recommended. Reference should be made to ISGOTT for additional guidance on entry into pumprooms.
S Shhiipp C Coonnssttrruuccttiioonn Ship Dimensions and Form General Cargo Vessel
These types of ships in general are built with longitudinal framing at the decks and in the double bottoms. Transverse framing is at the sides. Profile
The transverse strength is given by fitting transverses at the deck and plate floors are fitted in the double bottoms.
Longitudinal framing is not usual in general cargo vessels due to the high broken stowage involved. Also deep transverses then have to be fitted about 3.7 metres to give the ship transverse strength. Bilge wells are fitted with a cubic capacity of 0.17 cbm. Nowadays ceiling on top of tank tops are generally not fitted as such the plating is increased by 2mm. However where ceiling is fitted they should be removable in sections. The ceiling where fitted should have a clear space for drainage at least of 12.5mm. Cargo battens are fitted to the sides and to the turn of the bilges – size of 50mm thick and spacing between rows of 230mm. Midship
Shown above is a centre line bulkhead in the lower hold and in the tween deck. This extends from the transverse watertight bulkhead to the hatch coamings. Tankers These ships may have two or more longitudinal bulkheads – today with double hull concept at least 3 but normally 4.
The bottom and deck are also framed longitudinally and so are the sides and the sides of the longitudinal bulkheads. The length of a tank is not to exceed 0.2L. As the size of the tanker grows transverse wash bulkhead are fitted at about mid length of the tank. These are for size of tanks over 0.1L or 15m whichever is more. Centre line was bulk heads are fitted where the breadth exceeds the dimensions as laid out in the Rules for different size of tanks. Cofferdams are provided both forward of the oil carrying space as well as in from of the ER bulkhead. Generally the pumproom is located within the cofferdam aft. Some ships have a forward pump room located in the forward cofferdam. The cofferdams are to be at least 760mm in length Some smaller ships have a combined transverse and longitudinal framing system. In lieu of bulwarks these ships are to have open rails on deck. Cargo tanks are tested by a head of water in the cargo tank – 2.45m above the highest point of the tank. Generally a system of staggered test is undertaken. Alternate tanks are filled and the empty tanks is inspected. Once all the empty tanks are inspected, the filled tanks are empties and the reverse tanks are filled and the other alternates inspected. Inspecting of the tank welding are done by rafting within a tank. Profile
Plan
Midship
Bulk Carriers: These ships are characterised by their ability to carry cargo in bulk. If carrying grain and other lighter cargo all the holds are filled. However if heavy cargo such as iron ore is carried then alternate holds are filled and to the designed loads only. Profile
The vessel may be constructed on the combined system, longitudinal framing together with transverse framing which are fitted at the sides. The longitudinal framing is fitted in the double bottoms, the deck and the bottoms of the wing tanks. The wing tanks may be utilised to carry cargo as well as remain empty. They carry ballast water during the ballast passage. Transverse webs are fitted at in the wing tanks at intervals as laid out in the Rules. And side stringers are fitted at about 1/3rd and 2/3rd the depth of the tanks. Plan
Midship
Combination Carriers: These ships are capable of carrying ore as well as oil in bulk. Transverse bulkheads are usually of the cofferdam type with all the stiffening on the inside. There is a rise of floor of the inner bottom which facilitates drainage to the drain well arranged on the centre line. The pipelines run through a duct keel. The duct keep entrance in the pumproom has a oil and gas tight door. Profile
On the top the hatch covers are mainly the side rolling Macgregor type.
The hatch breadth is usually about 50% of the breadth of the beam. The main disadvantage of this type of ship is the stability – since they are not built with a longitudinal partition in the centre the free surface effect is enormous and this necessitates overall loading complexities. Plan
Together with this is the sloshing effect which tend to damage the fitting inside. The stability book would give the loading levels as well as the loading stability requirements as per the Rules. Midship
Container: Longitudinal framing is used throughout the main body length of the ship. Transverse framing is used on the fore part and the after part. Profile
The ships are built having a cellular construction at the sides. Strong longitudinal box girders are formed port and starboard by the upper deck – the second deck – top of the shell plating and top of the longitudinal bulkhead. The upper deck and the sheer strake form the box girder. These girders also provide stiffness against racking stresses and used as water ballast tank spaces. Midship
A form of bulkhead is fitted at intervals, centre to centre with water tight bulkheads being fitted as required by the Rules. The bulkhead gives support to the double bottom structure. The container guides consist of angle bars about 150mm x 150mm x 14mm thick connected to vertical webs and adjoining structure spaced 2.6m apart. The bottom of the guides is bolted to brackets welded to the tank top and beams. The brackets are welded to doubling plates, which are welded to the tank top. Ro – Ro Roll on Roll off ships have generally two ramps at either end of the ship to facilitate the loading of vehicles. The main characteristic of these types of ships is the clear decks un interrupted by transverse bulkheads. Deck heights are sufficient to accommodate the various types of vehicles carried. Profile
The lower decks may be used for carriage of cars while the upper may be used for the carriage of bigger vehicles. Transverse strength is maintained by fitting deep closely spaced web frames in conjunction with deep beams. These are usually fitted every 4th frame and about 3 m apart. The lower decks which are divided by watertight bulkheads have hydraulically operated sliding bulkhead doors which are opened while working cargo in port. The deck thickness is increased to take the concentrated loads; a reduction in the spacing of the longitudinals with an increase in size. A centre line row of pillars is fitted. Ramps are fitted at the bow and at the stern to facilitate the loading and discharging of vehicles. The separate decks are reached by fixed and sometimes hydraulically operated foldable operated ramps. A service car is provided within the ship to transfer the lashing gear to the different decks.
Midship
The stern ramps are generally set at an angle to the ships centre line to ensure that the ship can work cargo in any berth.
Passenger: The basic construction of these vessels follows the dry cargo vessel in their detail, a large number of decks being fitted. Profile
Each passenger ship is differently built with the naval architects and the classification societies agreeing on the various additions to the various pillars and bulkheads. However the basic rule and the provisions of SOLAS, MARPOL are complied with. Midship
Midship in way of ER
Definitions
Camber The purpose of rounding the beam is to ensure a good drainage of the water and also to strengthen the upper deck and the upper flange of the ship girder against longitudinal bending stresses- especially the compression stresses. Rise Of Floor This is the distance from the ‘line of floor’ to the horizontal, measured at the ship side. Purpose basically is to allow drainage of the double bottom water/ oil to the centre line suctions.
Tumblehome This is the inward slope of the side plating from the water line to the upper deck – today ships generally do not have a tumblehome. Flare This is the curvature of the side plating at the forward and gives additional buoyancy and thus helps to prevent the bows from diving too deeply into the water when pitching. The anchors are also clear when lowered from the flare of a ship.
Sheer This is the rise of ships deck fore and aft. This again adds buoyancy to the ends where it is needed during pitching. For calculating the freeboard a correction is applied for the sheer. In modern ship the after sheer has been greatly reduced.
Rake This is the slope, which the forward end has with between the bottom plating and the upper deck. The length between perpendiculars and the length overall difference is mostly due to the rake forward. It helps to cut the water and thus adds to the ships form.
Parallel Middle Body This is the part of the main body of the ship and it is a box like structure enabling maximum cargo carrying capacity. It also helps in the pushing when tugs are used to assist the vessel in berthing. Cargo stowage is also greatly facilitated. Entrance This part is the fore end of the ship and helps give the box like mid length a ship shaped structure. Run The after part similarly to the fore part entrance helps in giving the box like mid length a ship shaped structure and thus the handling of the vessel is enhanced.
“Length” means 96 per cent of the total length on a waterline at 85 per cent of the least moulded depth measured from the top of the keel, or the length from the fore side of the stem to the axis of the rudder stock on that waterline, if that be greater. In ships designed
with a rake of keel the waterline on which this length is measured shall be parallel to the designed waterline.
Moulded breadth: is the greatest moulded breadth – measured inside plating. Breadth (B) is the greatest moulded breadth of the ship at or below the deepest subdivision load line. Draught (d) is the vertical distance from the moulded baseline at midlength to the waterline in question. Depth and the draught both are measured from the top of the keel. The depth is measure from the top of the deck beam. If there is a camber then allowance is given as 1/3 rd of the camber. The rest of the meanings are all self-explanatory.
Definitions Forward perpendicular
This is represented by a line, which is perpendicular to the intersection of the designed load water-line with the forward side of the stem. After perpendicular A line represents this, which is perpendicular to the intersection of the after edge of the rudderpost with the designed load water line. This is the case for both single and twin-screw ships. For some ships having no rudderpost, the after perpendicular is taken as the centreline of the rudderstock. Length between perpendiculars This is the horizontal distance between the forward and after perpendiculars. Length on the designed load waterline This is the length, as measured on the water-line of the ship when floating in still water in the loaded, or designed, condition. Length overall This is the length measured from the extreme point forward to the extreme point aft. Base line This represents the lowest extremity of the moulded surface of the ship. At the point where the moulded base line cuts the midship section a horizontal line is drawn, and it is this line, which acts as the datum, or base line, for all hydrostatic calculations. This line may, or may not, be parallel to the load water line depending on the type of ship. Moulded depth This is the vertical distance between the moulded base line and the top of the beams of the uppermost continuous deck measured at the side amidships.
Moulded beam This is the maximum beam, or breadth, of the ship measured inside the inner shell strakes of plating, and usually occurs amidships. Moulded draught This is the draught measured to any water-line, either forward or aft, using the moulded base line as a datum. Extreme beam This is the maximum breadth including all side plating, permanent fenders etc. Extreme draught This is obtained by adding to the draught moulded the distance between the moulded base line and a line touching the lowest point of the underside of the keel. This line is continued to the FP and AP, where it is used as the datum for the sets of draught marks.
Load Lines and Draught Marks Deck line
The deck line is a horizontal line 300 millimetres in length and 25 millimetres in breadth. It shall be marked amidships on each side of the ship, and its upper edge shall normally pass through the point where the continuation outwards of the upper surface of the freeboard deck intersects the outer surface of the shell, provided that the deck line may be placed with reference to another fixed point on the ship on condition that the freeboard is correspondingly corrected. The location of the reference point and the identification of the freeboard deck shall in all cases be indicated on the International Load Line Certificate (1966). Freeboard. The freeboard assigned is the distance measured vertically downwards amidships from the upper edge of the deck line to the upper edge of the related load line. Freeboard deck. The freeboard deck is normally the uppermost complete deck exposed to weather and sea, which has permanent means of closing all openings in the weather part thereof, and below which all the openings in the sides of the ship are fitted with permanent
means of watertight closing. In a ship having a discontinuous freeboard deck, the lowest line of the exposed deck and the continuation of that line parallel to the upper part of the deck is taken as the freeboard deck. At the option of the owner and subject to the approval of the Administration, a lower deck may be designated as the freeboard deck, provided it is a complete and permanent deck continuous in a fore and aft direction at least between the machinery space and peak bulkheads and continuous athwartships. When this lower deck is stepped the lowest line of the deck and the continuation of that line parallel to the upper part of the deck is taken as the freeboard deck. When a lower deck is designated as the freeboard deck, that part of the hull which extends above the freeboard deck is treated as a superstructure so far as concerns the application of the conditions of assignment and the calculation of freeboard. It is from this deck that the freeboard is calculated. Load Line Mark
The Load Line Mark shall consist of a ring 300 millimetres in outside diameter and 25 millimetres wide which is intersected by a horizontal line 450 millimetres in length and 25 millimetres in breadth, the upper edge of which passes through the centre of the ring. The centre of the ring shall be placed amidships and at a distance equal to the assigned summer freeboard measured vertically below the upper edge of the deck line. The Load line rules which were brought in were due to the fact that the ships were being loaded in such a way that the ships were foundering. Thus the important fact to remember is that it was the freeboard that was being restricted, from very low to a safe figure. Depending on this freeboard the load line circle was marked as well as the other marks were made for different zones and densities. Thus the chapter on CONDITIONS OF ASSIGNMENT OF FREEBOARD is very important as it determines as to how much would be the distance between the deck line and the load line circle. Once this is determined the load line marks are painted, keeping the above in reference. The calculations give rise to the assigned summer freeboard.
Lines to be used with the Load Line Mark
The lines which indicate the load line assigned in accordance with these Regulations shall be horizontal lines 230 millimetres in length and 25 millimetres in breadth which extend forward of, unless expressly provided otherwise, and at right angles to, a vertical line 25 millimetres in breadth marked at a distance 540 millimetres forward of the centre of the ring.
The following load lines shall be used:
(a) The Summer Load Line indicated by the upper edge of the line which passes through the centre of the ring and also by a line marked S. (b) The Winter Load Line indicated by the upper edge of a line marked W. (c) The Winter North Atlantic Load Line indicated by the upper edge of a line marked WNA. (d) The Tropical Load Line indicated by the upper edge of a line marked T. (e) The Fresh Water Load Line in summer indicated by the upper edge of a line marked F. The Fresh Water Load Line in summer is marked abaft the vertical line. The difference between the Fresh Water Load Line in summer and the Summer Load Line is the allowance to be made for loading in fresh water at the other load lines. (f) The Tropical Fresh Water Load Line indicated by the upper edge of a line marked TF, and marked abaft the vertical line.
If timber freeboards are assigned in accordance with these Regulations, the timber load lines shall be marked in addition to ordinary load lines. These lines shall be horizontal lines 230 millimetres in length and 25 millimetres in breadth which extend abaft unless expressly provided otherwise, and are at right angles to, a vertical line 25 millimetres in breadth marked at a distance 540 millimetres abaft the centre of the ring. The following timber load lines shall be used: (a) The Summer Timber Load Line indicated by the upper edge of a line marked LS. (b) The Winter Timber Load Line indicated by the upper edge of a line marked LW. (c) The Winter North Atlantic Timber Load Line indicated by the upper edge of a line marked LWNA (d) The Tropical Timber Load Line indicated by the upper edge of a line marked LT. (e) The Fresh Water Timber Load Line in summer indicated by the upper edge of a line marked LF and marked forward of the vertical line. The difference between the Fresh Water Timber Load Line in summer and the Summer Timber Load Line is the allowance to be made for loading in fresh water at the other timber load lines. (f) The Tropical Fresh Water Timber Load Line indicated by the upper edge of a line marked LTF and marked forward of the vertical line. Where the characteristics of a ship or the nature of the ship’s service or navigational limits make any of the seasonal lines inapplicable, these lines may be omitted. Where a ship is assigned a greater than minimum freeboard so that the load line is marked at a position corresponding to, or lower than, the lowest seasonal load line assigned at minimum freeboard in accordance with the present Convention, only the Fresh Water Load Line need be marked. On sailing ships only the Fresh Water Load Line and the Winter North Atlantic Load Line need be marked. Where a Winter North Atlantic Load Line is identical with the Winter Load Line corresponding to the same vertical line, this load line shall be marked W.
Additional load lines required by other international conventions in force may be marked at right angles to and abaft the vertical line specified in paragraph (1) of this Regulation. Mark of assigning authority
The mark of the Authority by whom the load lines are assigned may be indicated alongside the load line ring above the horizontal line which passes through the centre of the ring, or above and below it. This mark shall consist of not more than four initials to identify the Authority’s name, each measuring approximately 115 millimetres in height and 75 millimetres in width. Details of marking
The ring, lines and letters shall be painted in white or yellow on a dark ground or in black on a light ground. They shall also be permanently marked on the sides of the ships to the satisfaction of the Administration. The marks shall be plainly visible and, if necessary, special arrangements shall be made for this purpose.
ZONES, AREAS AND SEASONAL PERIODS
The zones and areas are, in general, based on the following criteria: Summer - not more than 10 per cent winds of force 8 Beaufort (34 knots) or more. Tropical - not more than 1 per cent winds of force 8 Beaufort (34 knots) or more. Not more than one tropical storm in 10 years in an area of 5 square in any one separate calendar month. In certain special areas, for practical reasons, some degree of relaxation has been found acceptable. Tropical Zone
(1) Northern boundary of the Tropical Zone The northern boundary of the Tropical Zone is- the parallel of latitude 13N from the east coast of the American continent to longitude 60W, thence the rhumb line to the point latitude 10N longitude 58W, thence the parallel of latitude 10N to longitude 20W, thence the meridian of longitude 20W to latitude 30N and thence the parallel of latitude 30N to the west coast of Africa; from the east coast of Africa the parallel of latitude 8N to longitude 70E, thence the meridian of longitude 70E to latitude 13N, thence the parallel of latitude 13N to the west coast of India; thence the south coast of India to latitude 1030’N on the east coast of India, thence the rhumb line to the point latitude 9N, longitude 82E, thence the meridian of longitude 82E to latitude 8N, thence the parallel of latitude 8N to the west coast of Malaysia, thence the
coast of South-East Asia to the east coast of Vietnam at latitude 10N, thence the parallel of latitude 10N to longitude 145E, thence the meridian of longitude 145E to latitude 13N and thence the parallel of latitude 13N to the west coast of the American continent. Saigon is to be considered as being on the boundary line of the Tropical Zone and the Seasonal Tropical Area. (2) Southern boundary of the Tropical Zone The southern boundary of the Tropical Zone is- the rhumb line from the Port of Santos, Brazil, to the point where the meridian of longitude 40W intersects the Tropic of Capricorn; thence the Tropic of Capricorn to the west coast of Africa; from the east coast of Africa the parallel of latitude 20S to the west coast of Madagascar, thence the west and north coasts of Madagascar to longitude 50E, thence the meridian of longitude 50E to latitude 10S, thence the parallel of latitude 10S to longitude 98E, thence the rhumb line to Port Darwin, Australia, thence the coasts of Australia and Wessel Island eastwards to Cape Wessel, thence the parallel of latitude 11S to the west side of Cape York; from the east side of Cape York the parallel of latitude 11S to longitude 150W, thence the rhumb line to the point latitude 26S, longitude 75W, and thence the rhumb line to the west coast of the American continent at latitude 30S. Coquimbo and Santos are to be considered as being on the boundary line of the Tropical and Summer Zones. (3) Areas to be included in the Tropical Zone The following areas are to be treated as included in the Tropical Zone(a) The Suez Canal, the Red Sea and the Gulf of Aden, from Port Said to the meridian of longitude 45E. Aden and Berbera are to be considered as being on the boundary line of the Tropical Zone and the Seasonal Tropical Area. (b) The Persian Gulf to the meridian of longitude 59E. (c) The area bounded by the parallel of latitude 22S from the east coast of Australia to the Great Barrier Reef, thence the Great Barrier Reef to latitude 11S. The northern boundary of the area is the southern boundary of the Tropical Zone.
Seasonal Tropical Areas
The following are Seasonal Tropical Areas: (1) In the North Atlantic An area boundedon the north by the rhumb line from Cape Catoche, Yucatan, to Cape San Antonio, Cuba, the north coast of Cuba to latitude 20N and thence the parallel of latitude 20N to longitude 20W; on the west by the coast of the American continent; on the south and east by the northern boundary of the Tropical Zone. Seasonal periods: TROPICAL: 1 November to 15 July SUMMER: 16 July to 31 October. (2) In the Arabian Sea An area boundedon the west by the coast of Africa, the meridian of longitude 45E in the Gulf of Aden, the coast of South Arabia and the meridian of longitude 59E in the Gulf of Oman; on the north and east by the coasts of Pakistan and India; on the south by the northern boundary of the Tropical Zone.
Seasonal periods: TROPICAL: 1 September to 31 May SUMMER: 1 June to 31 August. (3) In the Bay of Bengal The Bay of Bengal north of the northern boundary of the Tropical Zone. Seasonal periods: TROPICAL: 1 December to 30 April SUMMER: 1 May to 30 November. (4) In the South Indian Ocean (a) An area boundedon the north and west by the southern boundary of the Tropical Zone and the east coast of Madagascar; on the south by the parallel of latitude 20S; on the east by the rhumb line from the point latitude 20S, longitude 50E, to the point latitude 15S, longitude 5130’E, and thence by the meridian of longitude 5130’E to latitude 10S. Seasonal periods: TROPICAL: 1 April to 30 November SUMMER: 1 December to 31 March. (b) An area boundedon the north by the southern boundary of the Tropical Zone; on the east by the coast of Australia; on the south by the parallel of latitude 15S from longitude 5130’E, to longitude 120E and thence the meridian of longitude 120E to the coast of Australia; on the west by the meridian of longitude 5130’E. Seasonal periods:
TROPICAL: 1 May to 30 November SUMMER: 1 December to 30 April. (5) In the China Sea An area boundedon the west and north by the coasts of Vietnam and China from latitude 10N to Hong Kong; on the east by the rhumb line from Hong Kong to the Port of Sual (Luzon Island) and the west coasts of the Islands of Luzon, Samar and Leyte to latitude 10N; on the south by the parallel of latitude 10N. Hong Kong and Sual are to be considered as being on the boundary of the Seasonal Tropical Area and Summer Zone. Seasonal periods: TROPICAL: 21 January to 30 April SUMMER: 1 May to 20 January. (6) In the North Pacific (a) An area boundedon the north by the parallel of latitude 25N; on the west by the meridian of longitude 160E; on the south by the parallel of latitude 13N; on the east by the meridian of longitude 130W. Seasonal periods: TROPICAL: 1 April to 31 October SUMMER: 1 November to 31 March. (b) An area boundedon the north and east by the west coast of the American continent;
on the west by the meridian of longitude 123W from the coast of the American continent to latitude 33N and by the rhumb line from the point latitude 33N, longitude 123W, to the point latitude 13N, longitude 105W; on the south by the parallel of latitude 13N. Seasonal periods: TROPICAL: 1 March to 30 June and 1 November to 30 November SUMMER: 1 July to 31 October and 1 December to 28/29 February. (7) In the South Pacific (a) The Gulf of Carpentaria south of latitude 11S. Seasonal periods: TROPICAL: 1 April to 30 November SUMMER: 1 December to 31 March. (b) An area boundedon the north and east by the southern boundary of the Tropical Zone; on the south by the Tropic of Capricorn from the east coast of Australia to longitude 150W, thence by the meridian of longitude 150W to latitude 20S and thence by the parallel of latitude 20S to the point where it intersects the southern boundary of the Tropical Zone; on the west by the boundaries of the area within the Great Barrier Reef included in the Tropical Zone and by the east coast of Australia. Seasonal periods: TROPICAL: 1 April to 30 November SUMMER: 1 December to 31 March. Summer Zones The remaining areas constitute the Summer Zones.
However, for ships of 100 metres (328 feet) and under in length, the area boundedon the north and west by the east coast of the United States; on the east by the meridian of longitude 6830’W from the coast of the United States to latitude 40N and thence by the rhumb line to the point latitude 36N, longitude 73W; on the south by the parallel of latitude 36N; is a Winter Seasonal Area. Seasonal periods: WINTER: 1 November to 31 March SUMMER: 1 April to 31 October
Reading Draughts: The following figure shows the draught marks between 11m and 12m.
It means that the mark is submerged up to the level of the mark, measurement of draught being from the bottom up. When the water is touching exactly the 11M mark at the bottom, only then is the draught read as 11m. anywhere above that is more than 11m. The height of the mark being 20cm, therefore the top of the 11m mark would read a draught of 11.20 m. The bottom of the decimal mark of 2 coincides with the top of the 11M mark and is to be read as 11.20m. The decimal marks are each 10 cm in height. Since the decimal marks are at – 2, 4, 5 and 8, the odd numbered decimal being ignored, thus the top of this 2 would read as 30 cm above the 11m mark or 11.30m. If the water level were at a position between the top of 2 and the bottom of 4 then the reading would be 11.35m.
Rest of the marks are self explanatory. If reading the draughts in choppy sea condition then the average of at least 5 readings would give a reasonable draught. Note do not read only the highest or the lowest since these may be due to out of the normal waves. For loading to draught marks – or when being surveyed for load line compliance, the draught may be used to check for overloading or submerging the load line mark. However it should be remembered that it is the freeboard that is being checked. For load line surveys the surveyor would mark a long baton (wooden) with the total length of the freeboard (summer) and others and then checks with the same against the deck line and the markings on the shipside (midship marks).
Ship Stresses Shear force and bending moments
When a section such as a beam is carrying a load there is a tendency for some parts to be pushed upwards and for other parts to move downwards, this tendency is termed Shearing. The Shear force at a point or station is the vertical force at that point. The shear force at a station may also defined as being the total load on either the left hand side or the right hand side of the station; load being defined as the difference between the down and the upward
forces, or for a ship the weight would be the downward force and the buoyancy would be the upward thrust or force. The longitudinal stresses imposed by the weight and buoyancy distribution may give rise to longitudinal shearing stresses. The maximum shearing stress occurs at the neutral axis and a minimum at the deck and keel. Vertical shearing stresses may also occur.
Bending Moment The beam, which we have been considering, would also have a tendency to bend and the bending moment measures this tendency. Its size depends upon the amount of the load as well as how the load is placed together with the method of support. Bending moments are calculated in the same way as ordinary moments that is multiplying force by distance, and so they are expressed in weight – length units. As with the calculation of shear force the bending moment at a station is obtained by considering moments either to the left or to the right of the station. Hogging and sagging Hogging – When a beam is loaded or other wise is subjected to external forces such that the beam bends with the ends curving downwards it is termed as hogging stress. For a ship improper loading as well as in a seaway when riding the crest of a wave the unsupported ends of the ship would have a tendency similar to the beam above.
Sagging – In this case the beam is loaded or other wise subjected to external forces making the beam bend in such a way that the ends curve upwards, this is termed as sagging. Similar with a ship if improper loaded or when riding the trough of a wave – with crests at both ends then the ship is termed to be sagging.
For Hogging the ship ends to curve downwards would mean that the weight/ load amidships is much less than at the end holds/ tanks. For Sagging the ship would have been loaded in such a manner that a greater percentage of the load is around the midship area. In a seaway the hogging and the sagging stresses are amplified when riding the crests and falling into the troughs. Thus especially for large ships there are two conditions in the stability software – Sea Condition and Harbour condition.
A ship loaded while set in the harbour condition may allow loading with hogging/ sagging stresses reaching a high level, when this state of loading is transferred to a Sea condition in the software the results would be catastrophic since now the wave motions have also been incorporated. Thus planning a loading should always be in the Sea Condition.
Discharging in port may be planned in the Harbour Condition. Hogging and sagging cause compressive and tensile stresses on the ship beam – notably on the deck and the keel structure. Water pressure and Thrust Pressure is force per unit area and water pressure is dependent on the head of the water column affecting the point of the measurement of the pressure. Let us assume an area of 1sq.m. then this area of water up to a depth of 1 m below the surface would have a volume of 1sq.m. x 1m = 1cbm and the weight of this volume would be 1cbm x density of the water = 1MT (assuming that it is FW) or 1000kgf, therefore the pressure exerted by this mass would be 1000kgf/sq.m. Similarly if now the depth of measurement is increased to 3m then the volume of this area subtending up to the 3m mark would be 1sq.m x 3 = 3cbm and the weight of the water would be 3MT or 3000kgf and the pressure exerted would be 3000kgf/sq.m. If now the liquid had not been FW but any other then the weight would be found by multiplying the volume by the density of the liquid. And thus the pressure exerted would be found.
If we now increase the area of the square of water plane would it make a difference in the pressure? Let us consider a area of 2000sq.m then the volume of this water at a depth of 1 m would be 2000cbm and the weight would be 2000MT (consider FW) and the pressure exerted would be 2000,000kgf/ 2000sq.m which would give us again 1000kgf/sqm, thus the pressure is independent of the area of the water plane. Thrust however is different, thrust is taken to be the total weight of the liquid over an area. Thus for the previous example the thrust would be 2000 tonnes.
Thus the thrust is given by: the area of the water plane x pressure head x density of the liquid. Thrust always acts at right angles to the immersed surface and for any depth the thrust in any of the directions is the same. The pressure head which is used in the above calculation of thrust is the depth of the geometrical centre of the area below the surface of the liquid. For a ship the thrust on the ship side changes as the depth increases, however the bottom is affected uniformly for a set depth. Centre of pressure of an area is the point on the area where the thrust could be considered to act. It is taken that the centre of pressure is at 2/3rds the depth below the surface for ordinary vertical bulkheads and at half the depth in the case of collision bulkheads.
Racking stress and its causes In a seaway as a ship rolls from one side to the other the different areas of the ship have motion which are dependent on the nature of the subject area. The accelerations are thus not similar due to the various masses of the different sections (although joined together). These accelerations on the ships structure are liable to cause distortion in the transverse section. The greatest effect is under light ship conditions.
Local Stresses Panting This is a stress, which occurs at the ends of a vessel due to variations in water pressure on the shell plating as the vessel pitches in a seaway. The effect is accentuated at the bow when making headway.
Pounding: Heavy pitching assisted by heaving as the whole vessel is lifted in a seaway and again as the vessel slams down on the water is known as pounding or slamming. This may subject the forepart to severe blows from the sea. The greatest effect is experienced in the light ship condition.
Stresses caused by localized loading Localized heavy loads may give rise to localized distortion of the transverse section. Such local loads may be the machinery (Main engine) in the engine room or the loading of concentrated ore in the holds.
Shearing force Curve The following example shown is for an old tanker in the ballast condition.
The compartments loaded are the Fpk tank, WB tanks 2P and 2S, WB tank 3C and other miscellaneous tanks in the after section of the tanker. The SF is calculated as per the manual with the multipliers having been set by the shipyard and approved by the classification society. If we are to assume that the ship is a beam then the loads are at the fore end – midship region and the after section which has the accommodation as well as the ER. The SF curve is reproduced and the maximum occur at frames 54 and between 68 to 72, this corresponds to the area on the ship – mid 4C and between 2C (aft to mid region). Note that the signs have changed between the frames 54 and 68 with a point between frames 59 to 63 (3C mid to aft) registering 0 value.
Bending Moment Curve The following example shown is for a old tanker in the ballast condition.
The compartments loaded are the Fpk tank, WB tanks 2P and 2S, WB tank 3C and other miscellaneous tanks in the after section of the tanker. The BM is calculated as per the manual with the multipliers having been set by the shipyard and approved by the classification society. If we are to assume that the ship is a beam then the loads are at the fore end – midship region and the after section which has the accommodation as well as the ER. The BM curve is reproduced and the maximum occur at frames 59 and 76, this corresponds to the area on the ship – 4C forward bulkhead and 2C forward bulkhead. Note that the signs have changed twice.
Hull Structure
Structural components on ships’ plans and drawings: frames, floors, transverse frames, deck beams, knees, brackets, shell plating, decks, tank top, stringers, bulkheads and stiffeners, pillars, hatch girders and beams, coamings, bulwarks
Bow and stern framing, cant beams, breasthooks
Description of standard steel sections: flat plate, offset bulb plate, equal angle, unequal angle, channel, and tee
Longitudinal, transverse and combined systems of framing on transverse sections of the ships Longitudinal framing – Open floors
Longitudinal framing – Plate floors
Transverse framing – Open floors
Transverse framing – Plate floors
Duct keel
Stress concentration in the deck round hatch openings Holes cut in the deck plating by way of hatchways, masts and others create areas of high local stress due to lack of continuity created by the opening. Compensation for loss of strength at hatch openings
Compensation around some of these openings may be overcome by increasing the sizes of the material used, buy a careful disposition of the material and by paying careful attention to the structural design.
Compensating for the stress concentration around hatch corners by rounding off the square hatch corner ends
The corners radiused to reduce the stress concentration
A hatch corner in plan view, showing the structural arrangements A transverse section through a hatch coaming, showing the arrangement of coamings and deep webs
Deck-freeing arrangements - scuppers, freeing ports, and open rails
Connection of superstructures to the hull at the ship’s side
A plane bulkhead, showing connections to deck, sides and double bottom and the arrangement of stiffeners
A corrugated bulkhead
Transverse bulkheads have vertical corrugations and fore and aft bulkheads have horizontal ones
The basic idea of a bulkhead in addition to the water tight integrity is to add to the girder strength of the ship beam. Thus for a transverse bulkhead, which extends from the port to the starboard side or vice versa, the framing is done in a vertical manner so that the compressive and the tensile stress may be reduced for the beam. Similarly for a longitudinal bulkhead which runs parallel to the shipside the framing is done vertically, again so that the additional strength would enhance the stress compensating effect of the ship beam.
Construction of the corrugated bulkhead
A fitted corrugated bulkhead
Purpose of bilge keels and their attachment to the ship’s side Bilge keels are fitted at the turn of the bilge to resist rolling. They also improve the steering qualities of the ship – though very slightly. The ends are to be gradually tapered and should not end on an un-stiffened panel.
Stress relieving while fitting the bilge keel
Hold drainage systems
The hold drainage system of older cargo vessels had limber board covered upper side of the tank side bracket areas. The drainage conduit was these areas and the pipelines were connected to the after ends, which passed through the lightening holes in the DB’s.
The limber boards were removable for cleaning as they were frequently damaged (edges) leaving gaps through which cargo residue would accumulate. Modern ships do not have the side bilges and have only a strum box at the after end of the holds and these are connected in the similar way to pipelines, which run through the DB’s.
Bow and Stern
Pounding and the additional provisions to withstand such pounding: Heavy pitching assisted by heaving as the whole vessel is lifted in a seaway may subject the forepart to severe blows from the sea. The greatest effect is experienced in the light ship condition. To compensate for this the bottom is strengthened from 0.5L to between 0.25L and 0.3L from forward depending on the block coefficient, unless the ballast draught forward is over 0.04L.
Bottom framed Longitudinally Longitudinals are to be spaced 1000mm apart between 0.2L and 0.3L from forward and 700mm apart between 0.2L from forward and the collision bulkhead. Plate floors are to be fitted alternate frames, side girders not more than 2.1m apart.
Bottom framed Transversely Frame spacing abaft 0.2L from forward is not to exceed 1000mm and between 0.2L and the collision bulkhead 700mm. Forward of the collision bulkhead 610mm. Plate floors are to be fitted at every frame. Intercostal side girders are to be not more than 2.2m apart with half height side girders not more than 1.1m apart, the girders extending as far as is practicable. Panting This is a stress, which occurs at the ends of a vessel due to variations in water pressure on the shell plating as the vessel pitches in a seaway. The effect is accentuated at the bow when making headway.
Panting arrangements are to extend 0.15L from forward and abaft the after peak bulkhead. Tiers of beams spaced not more than 2000mm apart vertically are to be fitted at alternate frames in the fore peak or below the lower deck above the water line if the forepeak is small. Alternatively perforated flats may be fitted in lieu of panting beams 2.5m apart vertically.
Tiers of beams are to be supported at the centreline by a partial wash bulkhead or pillars. Beams are to be bracketed to frames and the frames to which no beams are attached are to be
bracketed to the stringer. Stringer plates attached to the shell are to be fitted at each tier of beams. Abaft the collision bulkhead intercostals side stringers having the same depth as the frames are to be fitted in line with those forward of the collision bulkhead and are to extend aft for 0.15L from the fore end. Stringers may be omitted if the shell plating is of increased thickness. Abaft the after peak bulkhead the structure is to be efficiently stiffened by deep floors and tiers of beams in association with stringers spaced 2500mm apart vertically.
Stern Frame Stern frames may be cast/ forged or fabricated from steel plate. In the case of cast or forged steel frames they may be in one piece or in two or more sections riveted or welded together (thermit welding).
Where a riveted connection is used the two sections of the bar are scarphed together and the class rules for the scarph are 3D and the depth as one and one third D, where D is the depth of the bar used in the construction of the frame.
A scarph fitted in a rudder post should not be above the highest gudgeon. Cast steel and fabricated stern frames are to be strengthened at intervals by transverse webs. All stern frames are to be efficiently attached to the adjoining structure and the lower part of the stern frame is to be extended forward to provide an efficient connection to the flat plate keel. With larger stern frames there is a tendency for the whole stern or propeller post and adjacent sections to be fabricated.
Fittings Mechanical Hatch covers
The figures shown below illustrate the various parts of a mechanical hatch cover. These hatch covers may be made up of several individual pontoons (so named because prior to the
‘MacGregor’ type of rolling hatch covers the pontoons had to be individually lifted and battened down).
The pontoons (individual parts of the hatch covers) are connected to one another and can easily and quickly be rolled into or out of position leaving clear hatchways and decks. The normal practice for the lengthwise opening of hatches but sideways opening hatchways are found on large bulk carriers and OBO’s. The smaller versions are mainly operated either manually (using wire and winch) or
electrically. The larger ones are nearly all operated hydraulically. The wheels on the side on which the pontoons rollere are eccentric in their construction thus when in the battened (lowered) position the clearance between the wheel and the trackway is minimum and the pontoon sits on the trackway, the rubber gaskets being compressed by the compression bar.
The cross wedges are used to ensure the pontoon rubber gaskets compress against the compression bars of the forward pontoons. The side cleats ensure that the pontoons stay compressed to the trackway compression bar and the ship motion is effectively compensated or removed.
These hatch cover systems consist of various parts: The pontoons, eccentric wheels, trackway wheels, cross wedges, and the side cleats.
Battening down a hatch is to be done after reading the operations manual. A hatch cover should not be battened with cargo on top.
The Channels are to be swept prior battening so that the packing do not rest on dirt. The drain channel on the front of the hatch pontoons are to be cleaned prior closing the hatch.
Once the wheels are turned the next item to be engaged are the cross wedges and the side cleats are to be fitted last.
Prior proceeding to sea (long voyage) the hatch cover sealing should be tested with chalk marks made on all the compression bars – on the hatch coaming as well as on the pontoons. The hatch is to be battened and then opened to see if all the rubber gaskets have got chalk mark on them or not – if not hen rectification to be done.
Oil tight hatchcover
These hatch covers are small in size and may have butterfly nut locking arrangement. The sealing is done by Hi-nitrile rubber which is not affected by oil.
Manhole covers do not vary much in design, their shape however are sometimes different for different places. When fitted outside a tank they may be either circular or elliptical. But when fitted inside they are almost always elliptical to facilitate their removal. Usual size openings vary between 450mm to about 600mm.
Roller, Multi-angle, Pedestal and Panama fairleads
A roller is to be found on the forward and after stations area – generally at the leads to the mooring ropes as well as on top of ‘old man’ pedestals. These facilitate the hauling of ropes since they reduce the friction when the rope is hauled through a panama fairlead which has no rollers.
A panama fairlead is o named since they were mostly used in the Panama Canal. The ship is hauled by small locomotives and the wires are sent out through these leads – they are of adequate strength to prevent the metal being cut open by the wires.
A multi angle fairlead again is a fairlead used due necessity when in the great Lakes. The ship moves through numerous locks as the ship is made to climb a great height – the Welland Canal system itself uses about 13 lock gates to cross the Niagara falls. The movement of the ship being fast and the difference in height being enormous the ship steadies itself with 2 wires forward and 2 wires aft, when in the locks. These wires are passed through the multi angle fairleads to reduce the enormous friction generated.
Mooring bitts are prefabricated and then are welded onto the deck. The size of the bitts are dependent on their use. Thus a small set may be fitted next to an occasional winch while the larger ones are fitted at the mooring stations. The bitts are hollow and as such require care to ensure that the sides do not corroded and holed.
A typical forecastle mooring and anchoring arrangement, showing the leads of moorings
Securing anchors and making spurling pipes watertight in preparation for a sea passage Once the anchor has been washed the anchor is hove right up into the hawse pipe, the bow stopper is lowered and the locking pin inserted. The winch is reversed a little to make the chain sit properly into the slot of the bow stopper and then the brake is tightened and the windlass gear removed. The anchor chain at the deck level (hawse pipe) is lashed with extra lashings as provided by the shipyard, if none are present or if expecting heavy weather, then extra wire rope lashings are taken, The wire rope to be used should be tested one, if an old (good condition) life boat falls are available then this makes a very good extra lashing wire. This wire is flexible and can be used by hand. A number of turns (figure of eight) are taken around two sets of bitts. The free ends being fastened by bull dog clips at least two fixed in opposite directions. Generally the shipyard would have provide lashing point as well as short length of wire attached to a bottle screw. These should be well oiled and are the most efficient for lashing the anchor. The wire should be tight.
Once the anchor is lashed the hawse pipe covers are not placed but stowed under deck or in their stowage positions. The spurling pipe area is chipped to remove any residual remains of earlier cement. The metal spurling pipe covers are placed around the chain and over the spurling pile. The clips provided at the edges of the covers should be hooked to the lips of the spurling pipe. A new canvas cover is then placed over the metal covers just fitted and is tied around the lips of the spurling pipe as well as the chain. No empty spaces should be found. Cement mixture is prepared and the entire cover is covered with this mixture. Cable stopper
A chain stopper as shown below may be of various designs, but all serve the same purpose – to hold the cable. The cable is passed through the stopper – with the holding bar lifted up – by the counterweight on top. There is a pin to hold the bar in this position. Once the decision has been taken to hold the cable, the safety locking pin is removed and the bar is eased down on top of the cable. Note that the default position of the holding bar is to arrest the cable, only a effort is required to keep it up. Once the bar is placed over the cable the cable may have to be adjusted a little to ensure that the flat part of the cable falls in the holding area and not the vertical section, the safety locking pin is now introduced to prevent the bar from jumping u[ in case the cable slip from the brake. Once the lacking pin is in position the brake can be released and the stopper would do the work of holding the cable.
Masts and Sampson posts
Bilge and ballast piping system of a cargo ship
The following shows a bilge and ballast line diagram of a general cargo ship. The bilges are all fitted with non return valves so that not water may be inadvertently be pumped into the holds. The bilges are serviced by a bilge pump which incorporates a strainer and this should be checked before starting the pump.
The strum box fitted in the holds is to be kept clean and the perforations are to be checked that they are not closed due to muck and rust.
Same with the mud boxes in the ER fitted into the system.
Arrangement of a fire main
Capacity of fire pumps The capacity of the fire pumps is stated in SOLAS but need not exceed 25m3 per hour Arrangements of fire pumps and of fire mains
Ships shall be provided with independently driven fire pumps as follows: Passenger ships of 4,000 tons gross tonnage and upwards at least three Passenger ships of less than 4,000 gross tonnage and cargo ships of 1,000 tons gross tonnage and upwards at least two Cargo ships of less than 1,000 tons gross tonnage to the satisfaction of the Administration Sanitary, ballast, bilge or general service pumps may be accepted as fire pumps, provided that they are not normally used for pumping oil and that if they are subject to occasional duty for the transfer or pumping of oil fuel, suitable change-over arrangements are fitted. The arrangement of sea connections, fire pumps and their sources of power shall be such as to ensure that:
In passenger ships of 1,000 gross tonnage and upwards, in the event of a fire in any one compartment all the fire pumps will not be put out of action. In cargo ships of 2,000 gross tonnage and upwards, if a fire in any one compartment could put all the pumps out of action there shall be an alternative means consisting of a fixed independently driven emergency pump which shall be capable of supplying two jets of water to the satisfaction of the Administration. The pump and its location shall comply with the following requirements: The capacity of the pump shall not be less than 40% of the total capacity of the fire pumps required by this regulation and in any case not less than 25 m3/h. Number and position of hydrants
The number and position of hydrants shall be such that at least two jets of water not emanating from the same hydrant, one of which shall be from a single length of hose, may reach any part of the ship normally accessible to the passengers or crew while the ship is being navigated and any part of any cargo space when empty, any ro-ro cargo space or any special category space in which latter case the two jets shall reach any part of such space, each from a single length of hose. Furthermore, such hydrants shall be positioned near the accesses to the protected spaces. Pipes and hydrants
Mainly galvanised steel pipes are used and during repairs no doublers or such part renewals are allowed – change is flange to flange renewal. The arrangement of pipes and hydrants are to be such as to avoid the possibility of freezing. On cargo ships where deck cargo may be carried, the positions of the hydrants are to be such that they are always readily accessible and the pipes are to be arranged, as far as practicable, to avoid risk of damage by such cargo. A valve is to be fitted at each fire hydrant so that any fire-hose may be removed while the fire pump is at work.
The above figure shows a typical fire mains line. Note that the emergency fire pump is located away from the machinery space as per rules. Isolation valves are provided so that any system being damaged the other system may be used for example the port system and the starboard system. In the machinery space a separate pump (Fire and GS pump) is also coupled, this is generally used when washing decks, and as an emergency measure while the fire pump is being overhauled. Sounding pipes
Sounding pipes covers come with varied designs. That shown below is a sunken cap type generally the cap is made of brass. The justification being that of the two thread and cap assembly the thread of the brass is to wear out first and that of the deck pad. The renewal of the brass cap being inexpensive and convenient rather than the deck pad which entails hot work.
The metal cap (not sunken) type of covers have a chain attached to them to prevent their being washed overboard.
Air pipes to ballast tanks or fuel oil tanks
The above figure shows a design of air pipe cover. In normal condition – the ball remains at the bottom of the air pipe head and the tank breathes in and out through the vent. However in the event that the air pipe is submerged then the ball floats up and closes the opening at the top thus preventing any water from entering the tank. Sea spray and rain is prevented from entering the tank by the design of the head. It is totally enclosed and a rectangular plate, which leaves a small gap between the mesh and itself, allowing the breathing of the tank.
Fittings and lashings for the carriage of containers on deck
In the figure above the containers on deck are loaded on top of shoes which are welded on top of the deck as well on top of the hatch covers. Twistlocks are fitted on the shoes and the containers placed on the twistlocks. Hinged eyes are welded on deck to secure the container rod lashings.
Rudder and Propellers
The shape of a rudder plays an important part in its efficiency. The area of the rudder is approximately 2% of the product of the length of the ship and the designed draught. Since the vertical dimensions of the rudder are somewhat restricted due to the area constraint as mentioned above, the fore and aft dimensions are increased. Again due to this increased dimensions the torque necessary to turn this rudder is overcome by fitting balanced or semi balanced rudders. Such a rudder has about 1/3rd of the rudder area forward of the turning axis.
An ideal rudder is one where the centre of pressure and the turning axis coincide for all angles of the helm. An unbalanced rudder consists of a number of pintles and gudgeons, the top pintle being the locking pintle which prevents any vertical movement in the rudder and the pintle And gudgeon taking the weight of the rudder.
Principle of screw propulsion Some people still occasionally refer to the propeller as the “airscrew”, a very accurate and descriptive term that reflects the basic design and function of the propeller. Leonardo da Vinci had proposed the concept of a “helical screw” to power a machine vertically into the air. The propeller uses that principle to provide propulsion through the air, much like a threaded screw advances through a solid medium, with some notable exceptions, primarily related to the loss of forward movement because the medium is not solid. Nonetheless, the propeller is similar to a screw in some common features. First, the pitch of a propeller is the theoretical distance the propeller would move forward in one revolution (similar to a screw) and conceptually is the same as the pitch of a screw, namely the distance between threads if the propeller were a continuous helix. The second feature that relates to its screw design is that the angle of the blade changes along the radius, so that close to the hub, the angle is very steep and at the tip of the blade it is much more shallow. From a practical standpoint, this means that unless the pitch for a given propeller is known, it requires a trigonometric calculation to determine the pitch empirically. Thirdly, just as screws come in left hand and right hand threads, propellers have the same designation. When facing the water/ air flow if the top of the propeller moves to the right, it is designated “Right Hand” and if to the left it is “Left Hand”. (As viewed from the front a right hand propeller turns counterclockwise and a left hand propeller turns clockwise.) Propellers will frequently be stamped as “RH” or “LH”.
Propeller and some definitions
Boss or Hub The central portion of a screw propeller to which the blades are attached and through which the driving shaft is fitted. Rake
The point displacement, from the propeller plane to the generator line in the direction of the shaft axis. Aft displacement is considered positive rake (see Figure 2). The rake at the blade tip or the rake angle are generally used as measures of the rake. The strength criteria of some classification societies use other definitions for rake.
Skew The displacement of any blade section along the pitch helix measured from the generator line to the reference point of the section (see Figure 2). Positive skew- back is opposite to the direction of ahead motion of the blade section. The skew definition pertains to midchord skew, unless specified otherwise. Back (of blade) The side of a propeller blade which faces generally in the direction of ahead motion. This side of the blade is also known as the suction side of the blade because the average pressure there is lower than the pressure on the face of the blade during normal ahead operation. Tip
The maximum reach of the blade from the center of the propeller hub. It separates the leading edge from the trailing edge. Radius
Radius of any point on a propeller. Pitch
The pitch of a propeller is the theoretical distance the propeller would move forward in one revolution (similar to a screw) and conceptually is the same as the pitch of a screw, namely the distance between threads if the propeller were a screw. For this reason, propellers will frequently be stamped with a designation such as “D 2550/P2610”. This means that the diameter (in this case length of propeller or thickness of a screw) is 2.550 meters, and the pitch is 2.610 meters, so that in a mathematical sense, one revolution of this propeller would move it forward a distance of 2.610 meters.
Comparing fixed-pitch with controllable-pitch propellers Advantages of a controllable pitch propeller Allow greater manoeuvrability Allow engines to operate at optimum revs Removes need for reversing engines Reduced size of Air Start Compressors and receivers Improves propulsion efficiency at lower loads Disadvantages Greater initial cost Increased complexity and maintenance requirements Increase stern tube loading due to increase weight of assembly, the stern tube bearing diameter is larger to accept the larger diameter shaft required to allow room for Oil Tube Lower propulsive efficiency at maximum continuous rating Prop shaft must be removed outboard requiring rudder to be removed for all prop maintenance. Increased risk of pollution due to leak seals
Sketches the arrangement of an oil-lubricated sterntube and tailshaft
Stern tubes are fitted to provide a bearing for the tail end shaft and to enable a watertight gland to be fitted at an accessible position. The tube is usually constructed of cast steel with a flange at its forward end and a thread at the after end. It is inserted from forward and this end is bolted over packing to the after peak bulkhead. A large nut is placed over the thread at the after end, tightened and secured to the propeller post. In an oil lubricated stern tube the bearings are made of white metal. A gland is fitted to each end of the stern tube and since the after end gland will not be accessible during sea service it is made self adjusting. The flange shown is attached to the propeller so that it rotates with the shaft and oil tightness is obtained by a rotating gland. States how the propeller is attached to the tailshaft The after end of the tail end shaft is tapered to receive the propeller boss and a key is provided to transfer the torque from the shaft to the propeller. A nut fitted with a locking plate secures the propeller in position and as an additional safeguard it is fitted with a left hand thread in association with a right hand ed propeller or vice versa.
To remove the propeller and the tail end shaft the propeller should be slung on special eyes provide on the shell for this purpose – the rope guards removed – and the propeller nut slackened. The propeller is then started from the shaft by driving steel wedges between the boss and the propeller post. When it is free the nut is removed.
Cross-section of a shaft tunnel
S Sttaabbiilliittyy
Displacement Mass, Weight, Force and Gravity
Mass is the amount of matter that is contained within a body. The S.I. units of Mass are: Grammes Kilogrammes = 1000 grammes Metric ton = 1000 kilogrammes Force is the product of Mass and acceleration The S.I. Unit of force is: Kilogramme m/ s2 or Newton (N) Example: The car hit the tree with a great force. What would be the great force, this may be calculated by applying the above. However the car may not have been speeding or increasing the acceleration but may have been traveling at a constant speed, in that case we come to Momentum Momentum is the product of Mass and velocity. So in case of nautical terms the constant velocity of a ship is of great importance. If a ship bangs against a jetty with some velocity then there will be damage to the jetty but if the same ship reduces her speed or velocity then the impact damage will be considerably less. Coming back to Mass and Weight Weight and Mass are often confused in everyday life. Weight is actually the resultant force that acts on a body having some mass. Weight is thus a product of the mass of the body and the acceleration due to the earths gravity. So, the S.I. Units of Weight should actually be kg m/s2 or Newton (N)
Here since the acceleration due to gravity is known as 9.81m/s2 Therefore we may write: a mass of 1 kg having a weight of 1kg 9.81 m/s2 as 9.81 kg m/s2 Or simply 1 kgf, which is saying 9.81 N Or conveniently since 9.81 is constant on the surface of the earth We may write the weight to be: 1 kgf, this is the force that is being exerted on a mass of 1 kg. But if have to express this in Newton then it would be: 9.81 N However again since the gravity factor is common the unit of Weight is also expressed as kg. Thus: 1 tonne = 1 metric ton force = 1000 kgf Or 1 tonne is a measure of 1 metric ton weight. Moment is the product of force and distance The S.I. Units of Moment is the Newton-metre (Nm) Since we have seen that force is expressed in kgf or N and the S.I. Unit of distance kg is the metre Thus, 9.81 N = 1 kgf And, 9810 N = 1000 kgf or 1 tonne So, the unit generally used for large moments is the tonnes-metre Pressure is the force that acts on a body to cause it to change in some form. If it does not change and there is room for it to move then it does so. Pressure is thrust or force per unit area and is expressed as: Kilogrammes-force units per square metre or Kilogrammes-force units per square centimetre or for larger pressure in tonnes-metre (t/m2)
Density is defined as mass per unit volume or is expressed as unit of mass per unit of volume Or grammes/ cubic centimetre (gms/cc or gms/cm3) Fresh water has a density of 1 gm/cm3 or 1000kg/m3 Both are correct since: 1 kg is 1000 gms and 1 metre is 100 cm, since we are talking of cubic quantity 1 cubic metre would be 100x100x100 cubic cm So to equate it would be 1000 kg/m3 Or 1 t/m3 Thus the density of FW may be expressed as 1gm/cm3 or 1t/m3 Relative density is a factor without any unit. Relative density is expressed as the density of the substance divided by the density of FW Thus the RD of FW would be 1/1 or 1 And the RD of SW would be 1.025/1 or 1.025 So basically it is expressed as the same numerical value but without a unit. Archimedes found that when a body is immersed in water then the volume of water that overflowed as a result of this immersion was equal to the volume of the body. However the weight of the body plays an important part in this. Although the volume of the displaced water is the same as that of the body the weight may not be the same. Let us assume that a log of wood of dimension 1metre by 1metre by 12 metres is taken (thus the volume is 12 metre3, or 12 cbm), let the weight of the log be 8 t. (assumed density of the log at 0.667 t/m3) This log when it is fully immersed (using external force) in a tank full of water will make some water overflow, the quantity of water that would overflow would be 12 metre3, or 12 cbm But the weight of this water would be 12 t at the density of 1t/cbm
So we see that the weight of the water is more than the weight of the fully immersed log of wood and so the log will float. But at what level? Now if we remove the force that was holding the log underwater the log will bounce back to the surface and only a portion of the log will remain underwater. This amount will depend on the volume that it displaces and the weight of that displaced water. Both have to be equal. If we assume that only 67% of the log is immersed (12cbm x 0.67) then the volume of the water displaced would also be 8 cbm and its weight would be 8 t and that was the weight of the log. So the log would float in a state of equilibrium However the log would still be capable to taking extra load, and we can place weight on the log up to a maximum of 4t, any weight beyond that, and the log would sink. Let us work out the same example with a bar of iron of the same dimensions, thus the volume would be 12 cbm and at a density of iron at 7.86 gm/m3 the weight of the bar would be 94t. The volume of water that this bar would displace would be 12 cbm but the weight would be only 12 t. This being a much lesser figure than the weight of the iron bar, the iron bar would sink. Can we now make this bar of iron float? Yes, we can but we then need to flatten it out to a sheet of iron. We then need to bend the four edges so that the sheet is turned into a open cardboard box. This will give the iron sheet a much larger volume, the empty space on top of the sheet would also contribute to the volume but without adding to the weight (assuming the weight of air to be negligible) The sheet + air combination however has the same weight. Now it will float on the water at a level as determined by the weight of water that it would displace at that level.
Centre of Gravity is the point of a body at which all the mass of the body may be assumed to be concentrated. The force of gravity acts vertically downwards from this point with a force equal to the weight of the body. Basically the body would balance around this point. The Centre of Gravity of a homogeneous body is at its geometrical centre. Buoyancy and Centre of Buoyancy
So what makes the log or the open box iron sheet float. The fact that they are on the surface of the water is due to the earth’s gravity or the weight of the body. That it does not sink is due to Archimedes’ principle. We may also say that a force is pushing up the box. This force is dependent on the volume of the box within the water as well as its weight. This force is termed as the force of Buoyancy. It will act in case of a uniformly loaded box shaped vessel through the centre of gravity of the underwater volume of the box. However if the loading is not uniform, by which we mean that if say only the fore part is loaded with some other weight then obviously the underwater volume of the box will change and the centre of buoyancy will pass through centre of gravity of the new underwater volume of the box. Centre of Buoyancy can be defined as the geometrical centre of the underwater volume and the point through which the total force of buoyancy may be considered to act vertically upwards with a force equal to the weight of the water displaced by the body. Reserve Buoyancy
We have seen the condition of the sheet of iron, which was turned, into an open cardboard box, which floated very nicely on the surface of the water.
What happens if you now decide to tilt the box, depending on how high the edges are the water will enter the enclosed area and the combination of sheet+ air will become sheet + air + some water. This may make the box much more heavier than the weight of the volume of water displaced and the box would sink. Thus we require to put a water tight cover on the open box. This would ensure that no water would enter the open space within the box and the sheet+ air combination would remain intact and the box would float perpetually. Thus what we have created is Reserve buoyancy. A ship in a sea way floats on water, which may be calm and also may be rough. When in a rough seaway the ship rides the waves, the waves support sometimes the ends of the ship and then at the midway mark. In either of the case the ship would have a tendency to sink to a lower level since the weight of the ship and that of the water that it displaces would be different. Thus the requirement for a ship to have reserve buoyancy, to meet any eventual sea condition where more sheet + air combinations would be required to be brought into use. Coefficient of fineness of water-plane area (Cw): A ship floats on water. If at the water line the ship were to be cut off then the area at the water level is known as the ships water plane If we now divide this area of water plane with an imaginary rectangle having the length similar to the maximum length of the water plane and breadth similar to the maximum breadth of the water plane then this ration is termed as the coefficient of fineness of water plane area or Cw Cw
=
Area of water-plane/Area of rectangle ABCD
Similarly if we know the Cw at a particular draft then we may find the actual water plane area of the ship by measuring the maximum length and the greatest breadth. Area of the water-plane = L x B x CW The block coefficient of fineness of displacement (Cb): In exactly the same manner as we obtained the water plane area, if we were to measure the volume of the underwater part of the ship and divide this with the volume of a box having its length as that of the ship at that particular draft and breadth of the box as the maximum breadth of the underwater volume, then we would arrive at a ratio. This ratio is termed as the block coefficient of fineness of displacement, or
Cb
Cb at any particular draft is the ratio of the volume of displacement at that draft to the the volume of a rectangular block having the same overall length, breadth and depth. Knowing how the Cb was arrived at, we understand that for a box shaped vessel the ratio of Cb be 1. Also finer the lines of a ship the lower would be the Cb. Thus a VLCC would be tending towards 1, whereas a slender yacht or a warship would be closer to 0.5. Again this value of Cb would depend on the draft of that particular ship, since at the load draft a ship, even a small one appears quite box shaped but as the light draft is approached the fine curvature of the ship is apparent.
For merchant ship, this value (depending upon draft) will range from about 0.500 to 0.850, with some typical values as shown below: ULCC
–
0.850
General Cargo ships –
0.700
Oil tankers
–
0.800
Passenger ships
–
0.625
Bulk carriers –
0.750
Container / Ro-Ro
–
0.575
Tugs
–
0.500
Cb
=
Volume of displacement / L x B x draft
Therefore as in the case of Cw, the underwater volume of a ship may be found at that particular draft by: Volume of displacement
=
L x B x draft x Cb
The value of Cb is used to determine the carrying capacity of a Life Boat. In figure, the shaded portion represents the volume of the ships displacement at the draft concerned, enclosed in a rectangular block having the same dimensions.
SHIP’S LIFEBOAT BLOCK COEFFICIENT The problem of loading/ declaring the number of persons that it can carry in a Life Boat is that we do not have any load line marks to guide us. And even if there was one it would be difficult to embark looking at the load line mark. So how is the number of passengers determined for a life boat. The block coefficient of the boat is taken, in this case there is no need to launch the boat in the water and note the draft.
Say the If we accept that the Cb of wooden lifeboat is 0.6 Therefore, volume of the entire lifeboat would be given by L x B x draft x 0.6 cubic metres Now that the volume of the lifeboat has been found, the next step is to determine the number of persons that it would safely carry. To determine this the following is used and result is the closest whole number so obtained. Volume of the boat / volume of each person (both in cubic metres) Here the size of the person is generally not taken into consideration but the volume is adjusted with the length of the boat. For lifeboat lengths: 7.3 m or more the volume of a person is taken as 0.283 4.9 m the volume of a person is taken as 0.396 For intermediate boat lengths
the values are interpolated.
Effect of change of density on draft when the displacement is constant It has been already explained that the body floats on water at a particular level/ draft, as long as the weight of the body is equal to the weight of the volume of water that is displaced by the underwater volume of the body.
Thus the volume of the water depends on the underwater volume of the body, and The weight of this volume of water depends on the density of the water. Thus when a ship moves from water of a higher density to a water of lesser density, the weight of the water volume will become less. To compensate for this weight loss an additional volume of water has to be displaced, this is only possible if the underwater volume of the body is increased. So the body/ ship will sink lower in the water of a lesser density, or the draft will increase.
For box shaped vessels since the shape is uniform all the way from the top to the bottom, the walls being all vertical, it is easy to calculate the sinkage or the rising of the vessel with the change in the density. The resulting effect on box shaped vessels will be: New mass of water displaced = Old mass of water displaced New volume x New density = Old volume x Old density New Volume =
Old density
Old Volume
New density
But volume = L x B x draft L x B x New draft L x B x Old draft
=
Old density New density
New draft
=
Old draft
Old density New density
The resulting effect on ship shape vessels will be: New displacement = Old displacement New volume/Old volume = Old density/New density Due to the fact that the ships underwater shape is not like a box shaped vessel, the underwater volume does not linearly change. To find the change in draft of a ship shape, the FWA must be known. This is the number of mm that a ships draft changes when passing from SW to FW. FWA (in mm) = Displacement/(4 x TPC). When the density of the water lies between these two (SW & FW) then the value (in mm) that the ships draft changes when she enters the SW is called the Dock Water Allowance. DWA (in mm) = FWA (1025 – DW density)/25 Keeping the draft constant, in effect means that no load has been added or removed. But if the draft remains unchanged, even when the density of the water has changed implies that some change to the displacement has occurred.
Let us consider: A ship floats in the water at a certain draft, therefore the underwater volume of the ship displaces an equal volume of water. This volume of water when multiplied with the density of the water gives us the weight of the water, which again is equal to the weight of the whole ship. Now if the density of the water is reduced (travelling from SW to FW), the following would happen: The weight of the displaced water would become less. And consequently to compensate for this loss in weight an additional volume of water would have to be displaced.
To get an additional volume of water displaced means that the unde5rwater volume of the ship has to increase. If we do not want the underwater volume of the ship to increase then we have to remove weights fr0om the ship. Thus we see that to keep the draft constant, in a changing density scenario we have to either lighten the ship or we have add more weights to the ship. However, since the draft has not changed, the volume of water displaced also has remained unchanged. New vol. of water displaced = Old vol. of water displaced New displacement
=
New density New displacement Old displacement
Old displacement Old density
=
New density Old density
Tonnes per centimetre immersion (TPC) This is the mass that must be added/ or removed to a ship in order that the mean draft of a ship changes by a value of ONE centimetre. The figures that are given are for SALT WATER only and corrections have to be applied for obtaining the values in FW and in other dock waters. The TPC is not constant for the ship in all states of loading. The TPC changes as the underwater form changes, thus the TPC’s are given against the drafts. For every draft there is a different TPC, the most notable changes are between the light draft and the half way load draft, close to the summer draft the values changes are very small.. The Tonnes per Centimetre is therefore dependent on the underwater form of the ship and this is determined by the water plane at the surface of the water. So to calculate the TPC the water plane is essential. TPC = (water plane area x density of water) / 100 water plane area (WPA) is in m2
Density is in t/m3. Now let the mass ‘w’ tones be loaded such that the draft increases by 1 cm & the ship now floats at new Waterline W’L’ Since the draft increase is by 1 cm the mass loaded is equal to TPC. Also as the displaced water quantity increases by some amount, this weight of extra water displaced equals to TPC as well. Mass = Volume x Density = Area x 1/100 x 1.025 tonnes = 1.025A/100 tonnes TPCSW = 1.025 A/100 TPCFW = A/100 TPCDW
= (RDDW x TPCSW )/1.025
Note: TPC is always stated for Salt Water unless otherwise specifically mentioned. Effect of draft and density on TPC Since the TPC as has been seen is dependent on the 2 factors: 1. Water plane area – which determines the underwater volume of the ship 2. And the density of the water on which the ship is floating Thus if any of these two factors change the TPC will be affected. For box shaped vessels the 1st factor is not applicable since the shape is uniform all the way from the top to the bottom, the walls are all vertical. The 2nd factor of density needs to be attended to. As the density increases the TPC also increases. However for most ships being ship shaped meaning not box shaped, means that both the factors affect the TPC. The water plane area would change as the ship sinks deeper into the water or is lightened. Also the density affects the TPC in the same way as for a box shaped vessel.
TPC Curves
TPC is calculated for a range of drafts extending beyond the light and loaded drafts. This calculated TPC is then tabulated or plotted in a graphical form and these graphs are called the TPC curves. On board a ship the TPC’s are given in both a tabulated form alongside the drafts as well as in a graphical form. Displacement Curves
Displacement of the ship in SW (1.025) at various drafts is given in both a tabular form as well as in a graphical form. A displacement curve is one from which the displacement of the ship at any particular draft can be found, and vice versa. Fresh Water Allowance (FWA) In the basic principle of why a ship floats it is understood that the weight of the volume of water displaced by a ship is equal to weight of the entire ship. The volume of the displaced water is again equal to the volume of the underwater volume of the ship. Now when the weight of this displaced water is calculated we take the product of the volume of the water and the density of the water. So, if the density of the water changes, then the weight of the displaced water changes, the weight of the ship remaining unchanged. Thus to keep the ship floating something has to be adjusted and adjustment is in the underwater volume of the ship. So a ship floating in waters of different densities will do so at different levels. Thus to keep the ship floating something has to be adjusted and adjustment is in the underwater volume of the ship. So a ship floating in waters of different densities will do so at different levels. So we can replace the word level by the nautical word ‘draft’
Thus we may now define Fresh Water Allowance as the amount in millimetres by which a ships MEAN DRAFT changes when she moves between SALT WATER and FRESH WATER. As a ship moves from SW to FW, the weight of the displaced water reduces – RD of SW at 1.025 and FW at 1.000, so additional volume of water is required to float the ship, this means that the underwater volume of the ship has to increase so the ship sinks lower to compensate the above. So the draft increases. In the same way if a ship moves from FW to SW, the weight of the displaced water would be more than the weight of the ship, so the weight of the water has to be reduced, this may be reduced if the volume of the water is reduced, this again depends on the underwater volume of the ship, so the underwater volume of the ship is reduced. And so the ship rises a little and the draft of the ship reduces. FWA (in mm) = Displacement/ 4x ( (water plane area x density of water) / 100) Or FWA = Displacement / ( 4 x TPC)
Effect of draft on FWA: For box shaped vessel, FWA is the same at all drafts. For ship shaped vessels, FWA increases with draft. As the draft increases, both the displacement and the TPC increase, but the rate of change of displacement is higher than that of the TPC. Derivation of the FWA formula Consider a ship floating in SW at load Summer draft at waterline WL. Let volume of SW displaced at this draft be ‘V’.
Now let W1L1 be the waterline for the ship when displacing the same mass of fresh water. Let ‘v’ be the extra volume of water displaced in FW. Total volume of fresh water displaced will be V + v. Mass = Volume x density Mass of SW displaced = 1025V Mass of fresh water displaced = 1000 (V + v) But mass of FW displaced = Mass of SW displaced. 1000(V + v) = 1025V v = V/40
Assume that ‘w’ is the mass of SW in volume v and ‘W’ in volume V, Then, replacing the factor as obtained above we get: w = W/40 But w is a factor that is a product of the FWA and the TPC Now since the FWA is in mm and the TPC is in cm, they both have to be converted to metres Thus: W = (((FWA mm x 100)cm X TPC cm) / 100 ) metres Simplifying we have: w = (FWA x 100 x TPC) / 100 = W / 40 Or (FWA x TPC) = W / 40 But w = TPC x (FWA/10) Hence W/40 = TPC (FWA/10) or FWA = W/(4 x TPC). Where ‘W’ = Loaded SW displacement in tonnes. Mass = Volume x density
(22*100*12)/100=242=W/40
W=9680 9680/4/12=2420/12=242/1.2=22 Mass of SW displaced = 1025V Mass of fresh water displaced = 1000 (V + v) But mass of FW displaced = Mass of SW displaced. 1000(V + v) = 1025V v = V/40
TPC = (water plane area x density of water) / 100
Assume that ‘w’ is the mass of SW in volume v and ‘W’ in volume V, Then, replacing the factor as obtained above we get: w = W/40
Displacement = FWA x ( 4 x TPC) But w = TPC x (FWA/10) Hence W/40 = TPC (FWA/10) or FWA = W/(4 x TPC). Where ‘W’ = Loaded SW displacement in tonnes. Dock Water Allowance (DWA) As a ship sails the seas the SW density is assumed to be constant at 1.025 gms/cc, however the density of the SW is never the same everywhere, especially in partially enclosed salt water bodies, this does not make much difference since the depth of the water is very substantial. However when a ship enters a river from the sea the density of the water changes from SW to FW, gradually. The density of the river may never attain pure FW conditions and may be in between. Thus the need to calculate this intermediate correction for the new density. Docks (enclosed port areas containing jetties) have water that is intermediate between SW and FW, the water is brackish and may have a density of 1.010 gms/ cc. Thus Dock Water Allowance is similar to FWA and is the amount in millimetres by which the ships mean draft changes when a vessel moves between a salt water and dock water. Dock water is the water whose density is neither that of fresh water or salt water but inbetween the two. RD between 1.000 and 1.025. To get the correction in millimetres the formula that may be used is: (Please note however that the DWA allowed for should be for the minimum density that will be encountered by the ship while proceeding to the dock – this as a safety factor) DWA = (FWA (1025 – density of dock water)) / 25
Buoyancy The Laws Of Buoyancy
Floating objects possess the property of buoyancy.
A floating body displaces a volume of water equal in weight to the weight of the body. A body immersed (or floating) in water is buoyed up by a force equal to the weight of the water displaced. Centre of buoyancy
C of B can be defined as the geometrical centre of the underwater volume and the point through which the total force of buoyancy may be considered to act vertically upwards with a force equal to the weight of the water displaced by the body. For the purposes of freeboard computation, ships are divided into type “A” and type “B”. Type “A” ships A type “A” ship is one which: Is designed to carry only liquid cargoes in bulk; Has a high integrity of the exposed deck with only small access openings to cargo compartments, closed by watertight gasketed covers of steel or equivalent material; and Has low permeability of loaded cargo compartments.
Type “B” ships All ships, which do not come within the provisions regarding type “A” ships in above paragraphs, are considered as type “B” ships. Type “B” ships, which have hatchways fitted with hatch covers, are assigned freeboards based upon the values given in the rules. Conditions of equilibrium
The condition of equilibrium after flooding shall be regarded as satisfactory provided: The final waterline after flooding, taking into account sinkage, heel and trim, is below the lower edge of any opening through which progressive down flooding may take place. Such openings shall include air pipes, ventilators and openings which are closed by means of weather tight doors or hatch covers, and may exclude those openings closed by means of manhole covers and flush scuttles, cargo hatch covers, remotely operated sliding watertight doors, and sidescuttles of the non-opening type. However, in the case of doors separating a main machinery space from a steering gear compartment, watertight doors may be of a hinged, quick-acting type kept closed at sea, whilst not in use, provided also that the lower sill of such doors is above the summer load waterline. If pipes, ducts or tunnels are situated within the assumed extent of damage penetration, arrangements shall be made so that progressive flooding cannot thereby extend to compartments other than those assumed to be floodable in the calculation for each case of damage. The angle of heel due to unsymmetrical flooding does not exceed 15deg. If no part of the deck is immersed, an angle of heel of up to 17deg. may be accepted. The metacentric height in the flooded condition is positive. When any part of the deck outside the compartment assumed flooded in a particular case of damage is immersed, or in any case where the margin of stability in the flooded condition may be considered doubtful, the residual stability is to be investigated. It may be regarded as sufficient if the righting lever curve has a minimum range of 20deg. beyond the position of equilibrium with a maximum righting lever of at least 0.1 m within
this range. The area under the righting lever curve within this range shall be not less than 0.0175 m. rad. The Administration shall give consideration to the potential hazard presented by protected or unprotected openings, which may become temporarily immersed within the range of residual stability. The Administration is satisfied that the stability is sufficient during intermediate stages of flooding. EXAMPLE OF GRAVITY -VS- BUOYANCY
1 ton of steel
1 ton of steel
If the cube of steel is placed in water it sinks. There is not enough displaced volume for the forces of buoyancy to act upon. If the ship’s hull is placed in the water it will float. The larger volume of the ship’s hull allows the forces of buoyancy to support the hull’s weight. The ship’s hull will sink to a draft where the forces of buoyancy and the forces of gravity are equal. Displacement
The weight of the volume of water that is displaced by the underwater portion of the hull is equal to the weight of the ship. This is known as a ship’s displacement. The unit of measurement for displacement is the Metric Tonne.
Gravity
The force of gravity acts vertically downward through the ship’s center of gravity. The magnitude of the force depends on the ship’s total weight. Units Of Measure
Force: A push or pull that tends to produce motion or a change in motion. Units: Newton, etc. Parallel forces may be mathematically summed to produce one “Net Force” considered to act through one point. Weight: The force of gravity acting on a body. This force acts towards the center of the earth. Units: kilograms, etc. Moment: The tendency of a force to produce a rotation about a pivot point. This works like a torque wrench acting on a bolt. Units: Newton meters, etc. Moment = Weight x Lever Arm Volume = Length x Breadth x Height Volume: The number of cubic units in an object. Units: cubic metres (cbm), etc. The volume of any compartment onboard a ship can be found using the equation: Salt Water = 1.025 gms/cc Fresh Water = 1.00 gms/cc Diesel Fuel = 0.92 gms/cc
Calculating The Weight Of Flooding Water
A compartment has the following dimensions: Length = 20 M Breadth = 20 M Height = 8 M The compartment is now flooded with salt water to a depth of 6 M 1.
First, calculate the volume of water that has been added to the compartment.
Volume = Length x Breadth x Depth of Flooding Water = 20 M x 20 M x 6 M = 2400 cbm 2.
Second, multiply the volume of water by its specific gravity.
Stability Reference Points
M - Metacentre G - Center of Gravity B - Center of Buoyancy K - Keel
K - Keel: The base line reference point from which all other reference point measurements are compared. B - Center of Buoyancy: The geometric center of the ship’s underwater hull body. It is the point at which all the forces of buoyancy may be considered to act in a vertically upward direction.
The Center of Buoyancy will move as the shape of the underwater portion of the hull body changes. When the ship rolls to starboard, “B” moves to starboard, and when the ship rolls to port, “B” moves to port.
When the ship’s hull is made heavier, the drafts increase as the ship sits deeper in the water. “B” will move up.
When the ship’s hull is lightened, the drafts decrease as the ship sits shallower in the water. “B” will move down. The Center of Buoyancy moves in the same direction as the ship’s waterline.
G - Center of Gravity: The point at which all forces of gravity acting on the ship can be considered to act. “G” is the center of mass of the vessel. The position of “G” is dependent upon the distribution of weights within the ship. As the distribution of weights is altered, the position of “G” will react as follows:
1.
“G” moves towards a weight addition
2.
“G” moves away from a weight removal
3.
“G” moves in the same direction as a weight shift
M - Metacenter: As the ship is inclined through small angles of heel, the lines of buoyant force intersect at a point called the metacenter. As the ship is inclined, the center of buoyancy moves in an arc as it continues to seek the geometric center of the underwater hull body. This arc describes the metacentric radius.
As the ship continues to heel in excess of 7-10 degrees, the metacenter will move as shown.
The position of the metacenter is a function of the position of the center of buoyancy, thus a function of the displacement of the ship.
The position of “M” moves as follows: As the Center of Buoyancy moves up, the Metacenter moves down. As the Center of Buoyancy moves down, the Metacenter moves up.
Fresh Water Allowance Fresh Water Allowance (FWA) In the basic principle of why a ship floats it is understood that the weight of the volume of water displaced by a ship is equal to weight of the entire ship. The volume of the displaced water is again equal to the volume of the underwater volume of the ship. Now when the weight of this displaced water is calculated we take the product of the volume of the water and the density of the water. So, if the density of the water changes, then the weight of the displaced water changes, the weight of the ship remaining unchanged. Thus to keep the ship floating something has to be adjusted and adjustment is in the underwater volume of the ship. So a ship floating in waters of different densities will do so at different levels. Let us take the example of a ship with a weight of 10000 MT, let this ship float at a certain level (assume the water level is at the mid level of the ship) Then the underwater part of the ship would be displacing a volume of water that would be equal to the volume of the underwater part of the ship. Also the weight of this water would have to be equal to the entire weight of the ship. So we have, Displaced water = underwater part (volume) of the ship Weight of this displaced water = entire weight of ship We know,
Weight of this displaced water = volume of displaced water x specific gravity of the water So now if the specific gravity of the water changes, then to keep the weight of the water constant the volume of the displaced water has to change – and this is the reason that the ship either sinks lower or rises up when traversing from FW to SW and vice versa. Thus to keep the ship floating something has to be adjusted and adjustment is in the underwater volume of the ship.
So a ship floating in waters of different densities will do so at different levels. So we can replace the word level by the nautical word ‘draft’ Thus we may now define Fresh Water Allowance as the amount in millimetres by which a ships MEAN DRAFT changes when she moves between SALT WATER and FRESH WATER and vice versa As a ship moves from SW to FW, the weight of the displaced water reduces – RD of SW at 1.025 and FW at 1.000, so additional volume of water is required to float the ship, this means that the underwater volume of the ship has to increase so the ship sinks lower to compensate the above. So the draft increases. In the same way if a ship moves from FW to SW, the weight of the displaced water would be more than the weight of the ship, so the weight of the water has to be reduced, this may be reduced if the volume of the water is reduced, this again depends on the underwater volume of the ship, so the underwater volume of the ship is reduced. And so the ship rises a little and the draft of the ship reduces. FWA (in mm) = Displacement/ 4x ( (water plane area x density of water) / 100) Or FWA = Displacement / ( 4 x TPC) Effect of draft on FWA
For box shaped vessel, FWA is the same at all drafts. For ship shaped vessels, FWA increases with draft. As the draft increases, both the displacement and the TPC increase, but the rate of change of displacement is higher than that of the TPC.
Derivation of the FWA formula
Consider a ship floating in SW at load Summer draft at waterline WL. Let volume of SW displaced at this draft be ‘V’. Now let W1L1 be the waterline for the ship when displacing the same mass of fresh water. Let ‘v’ be the extra volume of water displaced in FW. Total volume of fresh water displaced will be V + v. Mass = Volume x density Mass of SW displaced = 1025V Mass of fresh water displaced = 1000 (V + v) But mass of FW displaced = Mass of SW displaced. 1000(V + v) = 1025V v = V/40 Assume that ‘w’ is the mass of SW in volume v and ‘W’ in volume V, Then, replacing the factor as obtained above we get: w = W/40 But w is a factor that is a product of the FWA and the TPC Now since the FWA is in mm and the TPC is in cm, they both have to be converted to metres Thus: W = (((FWA mm x 100) cm X TPC cm) / 100) metres Simplifying we have: w = (FWA x 100 x TPC) / 100 = W / 40 Or (FWA x TPC) = W / 40 But w = TPC x (FWA/10) Hence W/40 = TPC (FWA/10) or FWA = W/(4 x TPC). Where ‘W’ = Loaded SW displacement in tonnes.
Dock Water Allowance (DWA) As a ship sails the seas the SW density is assumed to be constant at 1.025 gms/cc, however the density of the SW is never the same everywhere, especially in partially enclosed salt water bodies, this does not make much difference since the depth of the water is very substantial. However when a ship enters a river from the sea the density of the water changes from SW to FW, gradually. The density of the river may never attain pure FW conditions and may be in between. Thus the need to calculate this intermediate correction for the new density. Docks (enclosed port areas containing jetties) have water that is intermediate between SW and FW, the water is brackish and may have a density of 1.010 gms/ cc. Thus Dock Water Allowance is similar to FWA and is the amount in millimetres by which the ships mean draft changes when a vessel moves between a salt water and dock water. Dock water is the water whose density is neither that of fresh water or salt water but inbetween the two. RD between 1.000 and 1.025. To get the correction in millimetres the formula that may be used is: (Please note however that the DWA allowed for should be for the minimum density that will be encountered by the ship while proceeding to the dock – this as a safety factor) DWA = FWA (1025 – density of dock water) 25
Movement of the Centre of Gravity Centre of gravity
It is the point of a body at which all the mass of the body may be assumed to be concentrated.
The force of gravity acts vertically downwards from this point with a force equal to the weight of the body. Basically the body would balance around this point. The COG of a homogeneous body is at its geometrical centre. Effect of removing or discharging mass
Consider a rectangular plank as shown. The effects of adding or removing weights would be as shown: Now cut the length of plank of mass ‘w’ kg whose CG is ‘d’ mtrs away from CG of the plank. Note that a resultant moment of ‘w x d’ kg m has been created in an anti-clockwise direction about ‘G’. The CG of the new plank shifts from ‘G’ to ‘G1’. The new mass (W-w) kg now creates a tilting moment of (W-w) x GG1 about G. Since both are referring to the same moment, (W-w) x GG1 = w x d GG1 = (w x d)/(W-w) CONCLUSION: When a weight is removed from a body, the CG shifts directly away from the CG of the mass removed, and the distance it moves is given by: GG1 = (w x d)/Final mass
metres
Where, GG1 is the shift of CG w is the mass removed d is the distance between the CG of the mass removed and the CG of the body.
Effect of adding or loading mass
Equating the tilting moments created due to the added weight, which must again be equal: (W + w) x GG1 = w x d GG1 = (w x d)/(W + w) GG1 = (w x d)/ (Final mass) Application to ships
DISCHARGING WEIGHTS: GG1 = (w x d)
metres
(Final displacement) LOADING WEIGHTS GG1 = (w x d) (Final displacement)
metres
metres
Shifting Weights GG2 = (w x d)
metres
(Displacement) Vertical Weight Shifts
Shifting weight vertically, no matter where onboard it is, will always cause the ship’s center of gravity to move in the same direction as the weight shift.
To calculate the height of the ship’s center of gravity after a vertical weight shift, the following equation is used: KG1 = ((W0 x KG0) +/- (w x kg)) / ΔF KGO = The original height of the ship’s center of gravity (M) Δo = The ship’s displacement prior to shifting weight (MT) w = The amount of weight shifted (MT) kg = The vertical distance the weight was shifted (M) ΔF = The ship’s displacement after shifting the weight (MT) (+) When the weight is shifted up use (+) (-) When the weight is shifted down use (-) Example Problem
10 MT of cargo is shifted up 3 M. ΔO is 3500 MT and KGo is 6 M. What is the new height of the ship’s center of gravity (KG1)? KG1 = ((Δo x KGo) +/- (w x kg)) / ΔF KG1 = ((3500 x 6) + (10 x 3)) / 3500 KG1 = 6.009 M Vertical Weight Additions/Removals
When weight is added or removed to/from a ship, the vertical shift in the center of gravity is found using the same equation.
KG1 = ((Δo x KGo) +/- (w x kg)) / ΔF KGO = The original height of the ship’s center of gravity (M) ΔO = Ship’s displacement prior to adding/removing weight (MT) w = The amount of weight added or removed (MT) kg = The height of the center of gravity of the added/removed weight above the keel (M) ΔF = The ship’s displacement after adding/removing the weight (+) When the weight is added use (+) (-) When the weight is removed use (-) Example Problem
A 30 MT crate is added 10 M above the keel. Δo is 3500 MT and KG0 is 6 M. What is the new height of the ship’s center of gravity (KG1)? KG1 = ((Δo x KGo) +/- (w x kg)) / ΔF KG1 = ((3500 x 6) + (30 x 10)) / 3530 KG1 = 6.034 M Horizontal Weight Shifts
Shifting weight horizontally, no matter where onboard it is, will always cause the ship’s center of gravity to move in the same direction as the weight shift. NOTE: A weight shift causing the ship’s center of gravity to move off centerline will always reduce the stability of the ship.
To calculate the horizontal movement of the ship’s center of gravity, the following equation is used: GG2 = (w x d) / ΔF w = The amount of weight shifted (MT) d = The horizontal distance the weight is shifted (M) ΔF = The ship’s displacement after the weight is shifted (MT) Example Problem A 50 MT weight is shifted 10 M to starboard. ΔO is 32000 MT.
What is the change in the center of gravity (GG2)? GG2 = (w x d) / ΔF GG2 = (50 x 10) / 32000 GG2 = 0.01562 M Horizontal Weight Additions/Removals
When an off-center weight is added or removed to/from a ship, the ship’s center of gravity will move off centerline, the ship will develop a list.
To calculate the horizontal movement of the ship’s center of gravity after adding/removing an off-center weight, the same equation is used: GG2 = (w x d) / ΔF w = The amount of weight added/removed (MT) d = The distance from the center of gravity of the weight to the ship’s centerline (M) ΔF = the ship’s displacement after the weight is shifted (MT) Example Problem 50 MT of cargo is loaded onto the Tween deck, 10 M from centerline. ΔO is 48000 MT. What is the change in the center of gravity (GG2)? GG2 = (w x d) / ΔF GG2 = (50 x 10) / 48000
GG2 = 0.0104 M
Effect of suspended weights
The CG of a body is the point through which the force of gravity may be considered to act vertically downwards. For a suspended weight, whether the vessel is upright or inclined, the point through which the force a gravity may be considered to act vertically downwards is g1, the POINT OF SUSPENSION.
Conclusions The CG of a body will move directly TOWARDS the CG of any weight ADDED. The CG of a body will move directly AWAY from the CG of any weight DISCHARGED. The CG of a body will move PARALLEL to the shift of the CG of any weight MOVED within the body. The shift of the CG of the body in each case is given by the following formula: GG1 = w x d
metres W
where w = weight added, removed or shifted. W = final mass of the body d = distance between the CG if weight added or removed, or the distance by which the weight is shifted. When a weight is SUSPENDED, its CG is considered to be at the POINT OF SUSPENSION.
Angle of Loll Angle of loll
Consider the following vessel in unstable equilibrium condition.
(effect of buoyancy) b GZ
w
01
w'
B
l'
B'
l
K
(effect of weight) w As the angle of heel increases, the CB moves out further until it is directly under G. The capsizing moment disappears now and this angle of heel at which this condition occurs is called the angle of loll.
The ship now moves around the angle of loll, but if the CB does not move out far enough to move directly under G, then the vessel will capsize.
(effect of buoyancy) b Z
w
M
w'
B
G b (effect of buoyancy)
0 l'
B'
G
l
Z
K
(effect of weight) w
(effect of weight) w Capsizing b=w If the heel increases beyond the angle of loll, the CB moves out further tocouple: the low side and the ship now moves around this angle.
(effect of buoyancy) b
(effect of buoyancy) b w
G
G
Z
02
w'
B
l'
B' l
K
Z w (effect of weight)
(effect of weight)w The angle of loll can be on either side depending upon the external inclining force, such as the wind and the waves. However, there is always the threat of the G rising above the M and this will create a situation of unstable equilibrium, thereby capsizing the ship. List Caused By Negative Gm
When a ship’s center of gravity moves vertically upwards and slightly above the Metacenter, the ship will develop a list (or possibly capsize.) The vessel may also “flop” over, developing the same list to the other side.
Possible Causes 1.
Removal of low weight
2.
Addition of high weight (ice)
3.
Moving weight upward
4.
Free Surface Effect
5.
Free Flow Effect (if present)
How to Recognize 1.
Vessel will not remain upright and will assume a list to either port or starboard.
2.
Vessel “flops” to port or starboard.
3.
Vessel will have a very long, slow roll period about the angle of list.
4.
A small GM is known to exist plus any of the above.
Corrective Measures 1.
Eliminate Free Surface and Free Flow Effects (if present)
2.
Add low weight symmetrically about centerline.
3.
Remove high weight symmetrically.
4.
Shift weight down symmetrically.
List Caused By Off-Center Weight And Negative Gm
The vessel’s stability is reduced by both an increase in the height of the center of gravity and movement from centerline. A negative GM condition exists, represented by the “uncorrected” curve. An off-center weight, represented by the cosine curve, is added and a larger list develops. Possible Causes 1.
A combination of the previous causes of list.
How to Recognize 1.
Vessel will assume a permanent list either port or starboard (vessel will not flop).
2.
Very slow roll period about this permanent list.
3.
The known off-center weight isn’t proportional to the ship’s list.
Corrective Measures Correct Negative GM first. a.
Eliminate Free Surface and Free Flow Effects (if present)
b.
Shift weight down, add weight low, or jettison weight high.
Correct for Gravity Off Centerline
a.
Add weight to higher side
b.
Remove weight from lower side
c.
Shift weight to higher side
*** ALWAYS correct Negative GM prior to shifting weights transversely ***
List Definitions
Roll: The action of a vessel involving a recurrent motion, usually caused by wave action. Heel: Semi-permanent angle of inclination caused by external forces, such as high-speed turns, beam winds, and seas. List: Permanent angle of inclination, caused by: 1. Ship’s Center of Gravity transversely shifted from centerline. 2. Negative Metacentric Height (-GM) 3. Combination of Gravity off-centerline and –GM Moment To Heel 1o Equation When a ship experiences an Inclining Moment (IM) the vessel will list or heel until the Righting Moment (RM) is equal to the Inclining Moment (RM = IM). The Inclining Moment is simply a force acting through some distance. IM = w x d This is only true when the ship has a negligible heel or list.
As the vessel inclines, the distance between the forces changes.
A relationship can be developed to solve for the distance between forces for all angles of heel. Using an expanded drawing of the triangle from the above diagram:
Using the cosine equation to solve for the distance X: X = d x cos θ Therefore: IM = w x d x cos θ A Righting Moment is created by the ship to keep itself upright. In this case, the force is equal to the ship’s displacement (WF) and the distance is the ship’s righting arm (GZ) at each particular angle of heel. RM = WF x GZ The Righting Arm (GZ) changes with inclination of the ship. Using the relationship derived for small angles of heel: GZ = GM x sin θ NOTE: This relationship holds true for angles less than 7°-10° Therefore: RM = GM x WF x sin θ The initial premise was that RM = IM: W x d x cos θ = GM x WF x sin θ Transferring cosine θ to the right: (sin θ / cos θ) = tan θ w x d = GM x WF x tan θ Choosing a specific angle, the moment (w x d) required to create that list or heel can be found. Using 1o: tan 1o = 0.01746 Therefore: MH 1˚ = GM x WF x 0.01746
This formula is valid for angles less than 10o due to movement of the metacenter. To check this formula for all inclinations less than 10o, a comparison between the MH10o and 10 times MH1o is made. MH 10˚ = GM x WF x tan 10˚ -vs-
10 x (MH 1˚ = GM x WF x 0.01746)
MH 10˚ = GM x WF x (0.01746) And 10 x (MH 1˚) = 10 x GM x WF x (0.01746) There is a 0.0017 difference over the 10˚range. This error is negligible. The list equation can now be used. LIST = (w x d) / MH 1˚
Example Your ship has a 1.5o list to starboard. There are 50 MT of cargo placed on the starboard side. The stevedores want to know how far to transfer the cargo to correct the list.
Step 1: Calculate MH1o: MH 1˚ = GM x WF x (0.01746) MH 1˚ = 0.8 M x 3500 MT x (0.01746) MH 1˚ = 48.8 M Step 2: Use the list equation to solve for distance: List = (w x d) / MH 1˚ Or, 1.5˚ = (50 MT x d) / 48.8 M d = (1.5 x 48.8) / 50 = 1.464 M
Example Your ship has a 2° list to port. The CO wants it corrected. There are 15 cbm of fuel in the port wing tank (sp.gr. 0.94). The starboard wing tank is empty. Correct the list using the fuel and a set of 5 cargo pallets (8 MT each). The cargo pallets may only be moved 5 M to starboard before hitting the bulkhead. How long will it take to correct the list? Pump capacity is 40 cbm per hour. WO = 12500 MT KM = 7.1 M KG = 6.02 M
Step 1: Calculate MH1°: MH 1˚ = GM x WF x (0.01746) MH 1˚ = (7.1 – 6.02) x 12500 x (0.01746) MH 1˚ = 235.7
Step 2: Calculate the amount of list corrected by shifting fuel: Weight of fuel = 15 x 0.94 = 14.1 MT List = (w x d) / MH 1˚ Or, List = (14.1 x 11) / 235.7 = 0.66˚ Step 3: So far, we have corrected 0.66o of the 2o list. Using the pallets, we will correct for the remaining 1.34o list. List = (w x d) / MH 1˚ or d = (1.34 x 235.7) / 40 = 7.9 M Step 4: Finally, calculate how long it takes to transfer 15 cbm of fuel when the pump capacity is 40cbm/ hour. Time = (15 cbm / 40 cbm/h) = 0.375 hr x 60 = 22.5 minutes Assuming it takes less than 22.5 minutes to move the 5 pallets, this is the time required to correct the list. Important: 1. When attempting problems on List, first find out the GM of the vessel (if the KG has to be calculated then do so) if it has not been stated. 2. If there are more than one shifting/ loading/ discharging involved then tabulate the moments and get the final moment (w x d) to either port or to starboard.
Example: A ship of 8000 tonnes displacement has KM = 8.7 m, and KG = 7.6 m. The following weights are then loaded and discharged: a. Load 250 tonnes cargo KG 6.1m and centre of gravity 7.6m, to starboard of the centre line. b. Load 300 tonnes fuel oil KG 0.6m, and centre of gravity 6.1m, to port of the centre line. c. Discharge 50 tonnes of ballast KG 1.2m, and centre of gravity 4.6m, to port of the centre line. Find the final list.
Weight
KG
Moment about Keel (VM)
Orig. Disp.
8000
7.6
60800
Load
250
6.1
1525
Load
300
0.6
180
Total
8550
Disch.
-50
Final Disp.
62505 1.2
8500
-60
62445
Final KG = Final Moment / Final displacement = 62445 / 8500 KG
=
7.34
KM =
8.7
Therefore, GM
w
=
1.36 Listing moment
d
Port
Stbd
250
7.6
1900
50
4.6
230
300
6.1
1830
From above we have Port: 1830 and Stbd: 2130 Therefore the final listing moment (w x d) = 300 to stbd. Now, MH 1˚ = GM x WF x 0.01746 List = (w x d) / MH 1˚
= 1.36 x 8500 x 0.01746
= 300 / 201.8376
= 1.49˚ to stbd.
= 201.8376
Inclining Experiment The inclining experiment is completed upon commissioning of the vessel. It is performed to obtain accurately the vertical height of the ship’s center of gravity above the keel (KG). Procedures: The shipyard at which the inclining experiment is to be performed will issue a memorandum to the ship outlining the necessary work to be done by ship’s force and by the yard to prepare the ship for inclining. 1. Liquid load will be in accordance with the memorandum. 2. Inventory of all consumables to be made by ship’s crew and inclining party. 3. Inclining weights are placed on centerline. 4. Freeboard is measured, and a photo of the drafts is taken. 5. Salinity of saltwater is measured. 8. Pendulums set up forward, midships, and aft. 9. Weights are moved off-centerline. 10.Inclination of the ship measured.
Measurements are taken for several weight movements both port and starboard. The Naval Architect then uses the following equation:
Where: w = Inclining Weights (LT) d = Athwartships Distance Weights Were Moved (FT) WF = Displacement of Ship (LT, with Inclining Weights) tan θ = Movement of Pendulum
Length of Pendulum
The inclining experiment measures GM accurately, and since the ship’s drafts are known, KM can be found, KG is then found using KG = KM - GM.
Free Surface Effect
Liquid that only partially fills a compartment is said to have a free surface that tends to remain horizontal (parallel to the waterline). When the ship is inclined, the liquid flows to the lower side (in the direction of inclination), increasing the inclining moment. Background:
If the tank contains a solid weight, and the ship is inclined, the center of buoyancy shifts in the direction of the inclination and righting arms (GZ) are formed.
Replacing the solid with a liquid of the same weight, when the ship is inclined, the surface of the liquid remains horizontal. This results in a transfer of “a wedge of water,” which is equivalent to a horizontal shift of weight, causing gravity to shift from G0 to G2.
The wedge of water transferred increases as the angle of inclination increases, therefore, the center of gravity shifts a different amount for each inclination.
Due to the horizontal shift of the center of gravity, the righting arm is now G2Z2. To determine the effect on stability, a vertical line is projected upward through G2 (see below). Where this line crosses the ship’s centerline is labeled G3. The righting arm G3Z3 is the same length as the righting arm G2Z2. Therefore, moving the ship’s center of gravity to position G2 or G3 yields the same effect on stability. Movement from G0 to G3 is referred to as a Virtual Rise of the center gravity.
To calculate the virtual rise in the center of gravity due to the Free Surface Effect, use the following equation:
B = The breadth (width) of the compartment L = The length of the compartment WF = The ship’s final displacement (after flooding water added) Factors Effecting Free Surface Effect Pocketing
Free Surface Effect can be reduced, to some extent, by creating pocketing. Pocketing occurs when the surface of the liquid contacts the top or bottom of the tank, reducing the breadth (B) of the free surface area. Since the effects of pocketing can not be calculated, it is an indeterminate safety factor. The Free Surface correction will therefore indicate less overall stability than actually exists.
Surface Permeability Impermeable objects (engines, pumps, piping systems, etc) inside a flooded space project through and above the liquid surface. These objects inhibit the moving water and the “shifting of the wedge” may or may not be complete, thus reducing Free Surface Effect. The impermeable objects also occupy volume, reducing the amount of flooding water (movable weight) that can fill the space.
Swash Bulkheads (Baffle Plates) In addition to some structural support, these bulkheads are designed to reduce Free Surface Effect. They are longitudinal bulkheads that hinder, but do not prevent, the flow of liquid from side to side as the ship rolls or heels. They are found in tanks, voids, double bottoms, bilges, etc.
Sluice Valves Free flow (Sluice) valves on tankers allow opposing tanks to be cross-connected. When large, partially filled tanks are connected, Free Surface Effect increases, and the vessel becomes less stable. Conditions of Free Surface Effect
1. FSE increases with increased length and width of compartment 2. FSE increases when displacement decreases (de-ballasting) 3. FSE is independent of the depth of the liquid
Example Problem The firemain ruptures, flooding a compartment with 0.91 metre of saltwater. Displacement prior to flooding was 4485 MT. The dimensions of the space are: L=9.14m B=12.8m Calculate the weight added by the flooding water:
2. Calculate the new displacement:
3. Calculate the virtual rise in G due to Free Surface Effect:
Free Flow Effect Free Flow Effect occurs when the ship’s hull is ruptured, allowing sea water to flow in and out as the ship rolls. This continuous weight addition and removal causes a horizontal shift in the center of gravity, which then equates to another virtual rise in the center gravity. Three conditions must exist for Free Flow Effect: The compartment must be open to the sea. The compartment must be partially flooded. The compartment must be off centerline or asymmetrical about centerline. When the vessel below is inclined, it experiences a horizontal weight shift due to the Free Surface Effect. The center of gravity shifts from G0 to G2. The center of gravity is shifted further from centerline due to the flooding weight addition/removal as the ship rolls. This reduces the righting arm from G2Z2 to G4Z4. By extending the line of gravitational force up to
the centerline, position G5 is found. This increase from G3 to G5 is the virtual rise of gravity due to the Free Flow Effect.
The virtual rise in the center of gravity due to the Free Flow Effect (G3G5) is found using the equation:
B = Breadth (width) of the compartment L = Length of the compartment Y = The distance from the center of gravity of the compartment to the Centerline of the ship WF = The ship’s displacement following damage The factors which minimize Free Surface Effect (pocketing, surface permeability, swash bulkheads, etc) will also minimize Free Flow Effect. There is one additional factor associated with Free Flow: the size of the hole in the ship. How the size of the hole affects Free Flow is not something that can be calculated. The FCE equation does not account for the hole. Basically, if the hole is small, less water will be added/removed to/from the ship. The larger the hole, the closer Free Flow Effect is to it’s calculated value.
Example Problem A vessel has a hole in the starboard side of a compartment. Displacement prior to damage was 3700 MT. Flooding depth is 1.52 m. Calculate the total virtual rise in the center of gravity (FSE + FCE). Compartment length is 9.14 and the breadth is 8.23m. The compartment extends from the Starboard shipside to a distance of 2.74 m beyond the centre line on the port side.
1. Calculate the weight added due to flooding water:
2. Calculate the ship’s final displacement:
3. Calculate the virtual rise in G due to Free Surface Effect:
4. Determine the distance “Y” for calculating the Free Flow Effect:
The center of the compartment is 4.11 m from the inboard bulkhead, and the ship’s centerline is 2.74 m from the inboard bulkhead. 5. Calculate the virtual rise in G due to Free Flow Effect:
6. Calculate the total virtual rise in the center of gravity: GG (virtual) = FSE + FCE = 0.11 + 0.038 = 0.148 m
Trim Trim
For a rectangular box shaped vessel, when a weight is added on to one side the vessel would list to that side. If however the weight is added either behind or ahead of the of the midship area but within the centre line partition of the ship then the vessel would get tilted either forward or aft. This tilting is known as TRIM Thus trim is the longitudinal equivalent of list. However there is a fundamental difference in the way the List and Trim are noted. List is as we know expressed in degrees, trim may be measured also in degrees but the expression is in Feet or Metres. Thus Trim may be defined as the difference between the draft at the fore perpendicular and the draft at the aft perpendicular. Unlike list which is stated as Port or Starboard, Trim is stated as Positive or Negative – more usually as Trim – meaning trimmed by stern, taken as positive. And Trim by head – meaning negative and that the draft ahead is more than the draft astern. Moment to Change Trim 1 cm (MCTC)
Now we have seen that to change the Trim we need to move weights in the fore and aft line of the ship. This then brings about a moment, and the moment required to change the trim by 1 cm is given by: MCTC = (W x GMl) / 100 x L Where W is the displacement of the vessel in tonnes GMl is the longitudinal metacentric height (m) L is the Length between perpendiculars (m) Centre of Floatation
This is the imaginary point where the ship pivots. It is the centre of gravity of the water plane area. The centre of Floatation is also referred to as the ‘Tipping Centre’ A box shaped vessel with a rectangular water plane area would have its centre of floatation amidships, whereas on a ship shaped vessel the centre of floatation would be either slightly forward or abaft of amidships. Remember all trimming moments are taken about the centre of floatation, since it is around this point that the vessel pivots. Change of Trim
This is the difference between a earlier trim and the latest trim. For example the trim that the vessel had on departure and the proposed trim that the vessel would have on arrival at the destination port. Longitudinal Metacentre (ML) In the manner of the Metacentre, the Longitudinal Metacentre is the point of intersection between the verticals passing through the centre of buoyancy when the vessel is on an even keel and when the vessel is trimmed.
Longitudinal Metacentric Height (GML) This is the vertical distance between the Centre of gravity of the vessel and the longitudinal Metacentre In the above figure we see that GG1 = (w x d) / W Or W x GG1 = w x d Trimming moment = W x GG1 = w x d
The vessel trims until G and B come in the same vertical line again Also take note that since the distance BG is very small as compared to BML, sometimes BML may be substituted for GML in calculations, without any appreciable error
Tan θ = trim / LBP = t /L where, trim in cm and LBP is in metres
Tan θ = GG1/ GML = (w x d) (W x GML) because GG1 = (w x d)/ W T/ 100L = (w x d) / (W x GML) T = (w x d) x 100L (W x GML) T = (w x d) / MCTC = Trimming Moment / MCTC Where Trim obtained will be in cm.
Trim = t / 100L Where L = LBP T – trim in cms To find the change of draft forward and aft due to change of trim Change of trim = Trimming Moment / MCTC Change of draft aft (cm) = (l x change of trim) / L Where: L is the distance of the centre of floatation from the aft perpendicular (m) L is the LBP (m) Change of draft forward (cm) = change of trim – change of draft aft Or Change of draft aft (m) = (L-l) / L x Change of Trim
Effect of loading, discharging or shifting weights
Loading / discharging at the centre of floatation will produce no change of trim but the draft will only change Only if the weight is shifted to either forward d or aft will we get a trimming effect. Shifting a weight will on the other hand give only a change of trim but not of draft So, loading can be considered as loading at the centre of floatation and then shifting to the desired place Similarly discharging can be considered as shifting to centre of floatation first and then taking the load off the ship Effect of loading, discharging or shifting weights So the two components to be calculated are: a. Change of draft b. Change of trim Then we go on to calculate the draft forward and aft Hence calculate these problems as follows: Bodily sinkage = W / TPC Then calculate the change of trim Change of trim (cm) = Trimming Moment / MCTC 3. Then calculate the change of aft draft – change of aft draft (cm) = l / L x COT 4. Then calculate the change of draft forward – change of draft forward (cm) = COT – change of draft aft OR (L-l) / L x COT
Curves of Statical Stability Load Line requirements for minimum stability conditions
The area under the GZ curve shall not be less than 0.55 m-rad up to an angle of 30° 0.09 m-rad up to an angle of either 40° or the lesser angle at which the lower edges of any openings which can not be closed weather-tight are immersed 0.03 m-rad between the angles of heel of 30° and 40° or such lesser angle as mentioned above The Righting Lever (GZ) shall be at least 0.20m at an angle of heel equal to or greater than 30° The maximum GZ shall occur at an angle of heel of not less than 30° Initial transverse metacentric height shall not be less than 0.15m. For ship carrying timber deck cargo complying with (a), this may be reduced to not less than 0.05 metres. Curve Of Statical Stability
Graph where GZ is plotted against the angle of heel. Drawn for each voyage condition by the ship’s officer. This curve is for a particular displacement and KG. From this curve it is possible to ascertain the following: Initial metacentric height – point of intersection of the tangent drawn to the curve at the initial point and a vertical through the angle of heel of 57.3° (1 radian). Angle of contraflexure – the angle of heel up to which the rate of increase of GZ with heel is increasing. Though the GZ may increase further, the rate of increase of GZ begins to decrease at this angle. The range of stability – where all GZ values are positive. The maximum GZ lever & the angle at which it occurs. The angle of vanishing stability – beyond which the vessel will capsize. The area of negative stability
The moment of statical stability at any given angle of heel (GZ x Displacement of the ship).
The moment of dynamical stability – work done in heeling the ship to a particular angle. Dynamical stability at è = W x A (in t-m-rad) W = Displacement (in tonnes) A = area between the curve and the baseline up to the given angle of heel (in metreradians).
GZ Cross Curves of Stability To draw the curve of statical stability, we need GZ values for various angles of heel. For this we use the GZ cross curves of stability. These curves are provided for an assumed KG, tabulating GZ values for various displacements and angles of list. Called cross curves because the various curves actually ‘cross’ each other. Since the curves are plotted for an assumed KG, if the actual KG differs from this a correction (GG1Sineθ) needs to be applied. This correction is positive if the actual KG is less than the assumed KG and vice-versa. After obtaining the GZ values at various angles, the curve of statical stability is prepared. KN Cross Curves of Stability
Same as the GZ cross curves and also used to get the GZ values for making the curve of statical stability. The only difference being that here the KG is assumed to be ZERO. This solves the problem of a sometimes positive and sometimes negative correction, as now the correction is always subtracted. GZ = KN – KG Sine θ
