SHIP HANDLING HANDLING NOTES FOR PHASE PHASE II Transverse Thrust on the propeller The force with which the water acts upon the propeller blades does not all act in the longitudinal direction but also has an athwartships component. This is known as transverse thrust – the expression that describes the imbalance from the water flow about about a propeller causing a vessel to swing to one side or another, most pronounced when the engines are operating astern . Going Ahead
If we look at a ship with one right-handed propeller (i.e. the propeller rotating in a clockwise direction when going ahead and as viewed from astern) and the rudder on the centre line the following situation is the norm: In the initial stages of the ship getting underway, the transverse thrust is directed to starboard and the ship’s turns to port. This is due the fact that the pressure from the water is higher on the propeller blades in their deeper position than in their shallower position, as the water above develops turbulence and air is sucked in. As the ship gradually increases her headway the turbulence is reduced and the pressure on the top blade increases. The thrust directed to starboard decreases and may in some ships be replaced by a thrust directed to port. This is, however, of no importance to manoeuving. Going astern
If we look at a ship with one right-handed propeller (i.e. the propeller rotating in an anti clockwise direction when going astern and as viewed from astern) and the rudder on the centre line the following situation is the norm: . The transverse thrust in this case directed to port and the ship will turn to starboard. The cause of the transverse thrust is the same as the going ahead case, there being higher pressure on the propeller blades in their deeper position, and the resulting thrust is directed to port. In addition, the water pressure on the starboard quarter will be higher than on the port quarter, since the water from the propeller blades is thrown upwards obliquely on the starboard side and downwards obliquely on the port side.
Thrusters Thrusters are normally installed at the bow, and/or the stern. Bow thruster is a small propeller in the forward part of the ship which helps to give a lateral movement to the vessel. The most common type is tunnel thruster. This thruster gets its name form the fact that a propeller is placed in a tunnel which runs transversely through the width of the ship. The thruster takes suction from one side and throws it out at the other side of the ship, thus moving the ship in the opposite direction. If the vessel has to be turned to port, the thruster takes in water from the port side and pushes it i t out from f rom the stbd s tbd side of the tunnel, thus creating a low pressure area on the port side and a high pressure area on the stbd side. The vessel then starts turning to port. The propeller is either a F-P-type (fixed pitch) or CP-type (controllable pitch). The most common way the propeller is powered is by an electric motor. In some ships, s hips, the power to the propeller is delivered by a hydraulic plant. It is essential to know the basic hydrodynamic physical laws to understand the working principle of thrusters •
Water has a fixed volume, it is practically impossible to dimnish its volume by applying pressure.
SHIP HANDLING NOTES FOR PHASE II •
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Water is a liquid and takes the shape of the vessel containing it and has a single horizontal surface. Water of equal temperature and density will always move horizontally into a low pressure area. Moving water creates a low pressure area close to its environment. Water made to move by means of a mechanical device ( that is any kind of impeller) can achieve a speed between 4 to 6 m/s.
In a tunnel thruster, the propeller is pumping water through the tunnel. The thrust created will be proportional to the amount of water passing through the tunnel. Greater the amount of water passing through the tunnel, greater will be thrust. Before the thruster is able to give any thrust at all, a flow of water through the tunnel must be created. To make all this possible, water leaving the tunnel must first create a passage through the water outside the tunnel. To do this energy is needed, the only source available is the water flow itself. As mentioned above, speed of water flow in the tunnel is between 4-6 m/sec. The only function of thruster is to pump as much water as possible through the tunnel in the shortest possible time. As the rd thruster is working on the reaction principle ( Newton’s 3 law), the water flow alone is required to give action and reaction (thrust). If the diamter of the tunnel is 2m and the ship is moving ahead at 4 kts ( 2m/sec approximately) , the water flow from the tunnel must make a new passage at every second. To do this, it needs energy. This energy is taken from the action resulting in reduced reaction ( thrust). If the speed is increased to 8 kts ( 4 m/sec), the water flow has to make a new passage every 0.5 sec. From this it can be seen that if the speed is increased, more energy is needed to make it possible for the water flow from the tunnel to escape and hence less thrust will be available to turn the ship
Depending on the movement of the vessel and the position of the pivot point, the effect of the thruster varies according to its distance from the pivot point. If the lever is large, the effect is more. 1. When the vessel is stopped, the pivot point is somewhere in the midship. th 2. When the vessel has headway, the pivot point is about 1/4 of the ship’s length from the bow. th 3. When the vessel has sternway, the pivot point is about 1/4 of the ship’s length from the stern. A bow thruster will have maximum effect when the vessel has a sternway because the pivot point will be aft and the thruster works on a respectable turning lever. A bow thruster when worked upon with a judicious use of the engines (small kicks) can provide a lateral movement to the vessel and be very helpful in berthing and unberthing. This ofcourse depends on the type of propeller, whether it is a right handed propeller or a left handed propeller. The type of propeller will not effect the thruster but will decide which side the lateral thrust will be efficient and easier to excecute. When a vessel is stopped and thruster is used it is often seen that the vessel starts to creep ahead. This is because when the bow thruster is moved, it draws in water from the forward of the ship thus creating a low pressure area in the forward of the ship. In the similar manner to a bank effect or interaction the ship will tend to smell the low pressure area and will slowly creep ahead. For example when a right handed propeller has to be berthed port side alongside: 1. The vessel comes almost abeam to the jetty with no headway, 2. Give small ahead kicks on the engines with the rudder to starboard, this will tend the bow to swing to stbd and the stern to port. 3. Use the bow thruster in a controlled manner to arrest the movement of the bow to stbd. 4. In this way the use of thruster and engine gives a lateral movement to the vessel to port.
Advantages
SHIP HANDLING NOTES FOR PHASE II 1) Better maneuverability at low speeds of the ship. 2) Safety of the ship increases when berthing in bad weather. 3) Saves money due to reduction of stay in port and less usage of tug boats. Disadvantages 1) A very large induction motor is required, which takes a lot of current and load, and thus large generator capacity is required. 2) Initial investment is high. 3) Maintenance and repairs are costly when there is damage.
Dangerous ship responses in following and quartering seas Following and/or quartering sea
The definition of a following and/or quartering sea is a wave direction which is coming form between right astern and 45 degrees on either quarter from right astern How to avoid dangerous conditions
Parametric roll An unstable and large amplitude roll motion will take place if the wave period encountered is approximately equal to half of the natural roll period of the ship. Parametric roll is one of those destructive phenomena that depend on a set of coincidences so finely balanced as to make the occurrence seem nearly impossible: ! The ship's geometry has to have certain characteristics; ! Its length has to be comparable to the wavelength of the sea conditions through which it is passing; ! And its speed must bear a certain relationship to both the wavelength and the vessel's natural rolling frequency. Parametric rolling may occur in two different situations. ! The stability varies with an encounter period Te that is about equal to the roll period Tr of the ship. The stability attains a minimum once during each roll period.This situation is characterized by asymmetric rolling. ! The stability varies with an encounter period Te that is approximately equal to half the roll period Tr of the ship. The stability attains a minimum twice during each roll period Its direct cause appears to be the periodic changes of roll stability in waves. More specifically, the ship's stability seems to be increasing when the ship is in the wave's trough and decreasing when she is in the waves crest. In its turn, the variations in stability seem to relate to the hull form. Slender lower hulls with immense bow flare and increased stern overhung can be particularly affected by parametric rolling.
SHIP HANDLING NOTES FOR PHASE II
Ship on the wave crest. Waterline is thinner in this condition
Ship in the wave trough. Waterline is fuller than that of still water
Under these conditions the ship's metacentric height (GM) changes dramatically as it is mainly affected by waterplane area. Wide waterplane area leads to big GM and narrow to smaller. This difference can be quite big ( see figure ).
For avoiding parametric rolling in following, quartering, head, bow, or beam seas the course and speed of the ship should be selected in a way to avoid conditions for which the encounter period is close to the ship roll period i.e Te = Tr OR the encounter period is close to one half of the ship roll period i.e Te= 0.5.Tr
Surf- riding and Broaching-to
SHIP HANDLING NOTES FOR PHASE II When a ship is situated on the steep forefront of a high wave in following or quartering sea conditions, the ship can be accelerated to ride on the wave known as surf riding. In this situation the so called broaching-to phenomenon may occur which endangers the ship to capsizing as a result of a sudden change of the ships heading and unexpected large heeling. Ships in following and quartering seas may not be able to keep constant course despite maximum steering efforts which may lead to extreme angles of heel. To broach means the ship is being driven off course sideways into the waves creating a danger of swamping or capsizing. In any major storm at sea it is important to keep the bow into the waves in order to avoid broaching or being pooped (water over the stern). Hurricane strength winds can overwhelm a ships ability to keep proper steerage making them vulnerable to broaching and capsizing. Broaching is an unintentional change in the horizontal-plane kinematics of a ship. Broadly, it may be described as the loss of heading by an actively steered ship that is accompanied by an uncontrollable build-up of large deviation from the desired course. Broaching is more commonly arising in waves which come from behind and propagate in a direction forming a small angle, say 10-30 deg, with the longitudinal axis of the ship. Although the inception of broaching represents a problem of instability on the horizontal plane, capsize may be incurred at the post-critical stage due to development of large heel as energy is transferred into the roll direction. Broaching could happen to small as well as to larger ships. It is notable however that the dynamics involved do not seem to fit always into a single pattern. Frequently, broaching is manifested as a sudden divergent yaw, which peaks within a single wave length. Control is lost when the middle of the ship lies somewhere on the down-slope and nearer to the trough. In other cases there is a gradual, oscillatory-type build-up of yaw as successive waves impinge on the ship from behind. In moderate sea states a ship is more likely to broach-to if it runs with a high speed and is slowly overtaken by the waves. Broaching may also occur at lower speeds if the waves are very steep.
OPERATIONAL PROVISIONS AGAINST CAPSIZING Compliance with the stability criteria does not ensure immunity against capsizing, regardless of the circumstances, or absolve the master from his responsibilities. Masters should therefore exercise prudence and good seamanship having regard to the season of the year, weather forecasts and the navigational zone and should take the appropriate action as to speed and course warranted by the prevailing circumstances. Care should be taken that the cargo allocated to the ship is capable of being stowed so that compliance with the criteria can be achieved. If necessary, the amount should be limited to the extent that ballast weight may be required. Before a voyage commences, care should be taken to ensure that the cargo, cargo handling cranes and sizeable pieces of equipment have been properly stowed or lashed so as to minimize the possibility of both longitudinal and lateral shifting, while at sea, under the effect of acceleration caused by rolling and pitching. A ship, when engaged in towing operations, should possess an adequate reserve of stability to withstand the anticipated heeling moment arising from the tow line without endangering the towing ship. Deck cargo on board the towing ship should be so positioned as not to endanger the safe working of the crew on deck or impede the proper functioning of the towing equipment and be properly secured. Tow line arrangements should include a method of quick release of the tow. The number of partially filled or slack tanks should be kept to a minimum because of their adverse effect on stability. It is advisable to avoid excessive values of metacentric height, since these might lead to acceleration forces which could be prejudicial to the ship, its complement, its equipment and to safe carriage of the cargo. Slack tanks may, in exceptional cases, be used as a means of reducing excessive values of metacentric height. In such cases, due consideration should be given to sloshing effects.
SHIP HANDLING NOTES FOR PHASE II All doorways and other openings, through which water can enter into the hull or deckhouses, forecastle, etc., should be suitably closed in adverse weather conditions and accordingly all appliances for this purpose should be maintained on board and in good condition. Weathertight and watertight hatches, doors, etc., should be kept closed during navigation, except when necessarily opened for the working of the ship and should always be ready for immediate closure and be clearly marked to indicate that these fittings are to be kept closed except for access. Weathertight and watertight hatches, doors, etc., should be kept closed during navigation, except when necessarily opened for the working of the ship and should always be ready for immediate closure and be clearly marked to indicate that these fittings are to be kept closed except for access. Any closing devices provided for vent pipes to fuel tanks should be secured in bad weather.
Ship handling in heavy weather In all conditions of loading necessary care should be taken to maintain a seaworthy freeboard. In severe weather, the speed of the ship should be reduced if propeller emergence, shipping of water on deck or heavy slamming occurs. Special attention should be paid when a ship is sailing in following, quartering or head seas because dangerous phenomena such as parametric resonance, broaching to, reduction of stability on the wave crest, and excessive rolling may occur singularly, in sequence or simultaneously in a multiple combination, creating a threat of capsize. A ship’s speed and/or course should be altered appropriately to avoid the above mentioned phenomena Reliance on automatic steering may be dangerous as this prevents ready changes to course which may be needed in bad weather. Water trapping in deck wells should be avoided. If freeing ports are not sufficient for the drainage of the well, the speed of the ship should be reduced or the course changed, or both. Freeing ports provided with closing appliances should always be capable of functioning and are not to be locked. In severe weather, the lateral wind pressure may cause a considerable angle of heel. If anti-heeling measures (e.g. ballasting, use of anti-heeling devices, etc.) are used to compensate for heeling due to wind, changes of the ship’s course relative to the wind direction may lead to dangerous angles of heel or capsizing. Therefore, heeling caused by the wind should not be compensated with anti-heeling measures, unless, subject to the approval by the Administration, the vessel has been proven by calculation to have sufficient stability in worst case conditions (i.e. improper or incorrect use, mechanism failure, unintended course change, etc.). Guidance on the use of anti-heeling measures should be provided in the stability booklet The dynamic behaviour of a ship in following and quartering seas is very complex. Ship motion is three dimensional and various detrimental factors or dangerous phenomena like additional heeling moments due to deck-edge submerging, water shipping and trapping on deck or cargo shift due to large roll motions may occur in combination with the above mentioned phenomena simultaneously or consecutively. This may create extreme combinations which may cause ship to capsize Synchronous rolling motion
Large rolling motions may be excited when the natural rolling period of a ship coincides with the wave period encountered. When navigating in following and/or quartering seas this may happen when the transverse stability of the ship is marginal and therefore the natural roll period becomes longer. The master should prevent a synchronous rolling motion which will occur when the wave period encountered (TE)is nearly equal to the natural rolling period of the ship (TR). Large rolling motions which occur under the condition (T E ~******T R /2, (which is parametric rolling)should also be prevented. The wave period encountered (TE)is a function of (V/T). By using this relationship, the master will know whether his ship will encounter synchronous and/or parametric rolling. When reducing speed in order to avoid any of above critical conditions, the master should take into consideration the minimum speed required for maintaining course control in wind and waves.
SHIP HANDLING NOTES FOR PHASE II Explanation of operation guidance Definition of symbols used L
length between perpendiculars of the ship (in metres)
B
breadth of the ship’s (in metres)
D
draught of the ship’s hull (in metres)
V
actual ship’s speed (in knot)
T
mean wave period (in seconds)
TE
wave period encountered (in seconds)
TR
natural rolling period (in seconds)
GM
metacentric height of ship (in metres)
****
average length of the wave (in metres)
** Encounter angle between the ship and the wave (degrees), H1/3
significant wave height (in meters)
Method of obtaining data necessary to use operation guidance
1.
V:
estimate the actual ship speed in an appropriate way.
2. X: obtain by visual observation. The wind direction can be usedas a reference for the wave direction. If the sea condition is not visible, the radar image can show wave crest trains and wave direction. 3. T: measure the period of the heaving motion of foam on the sea surface; generated by the breaking wave, with the use of a stop watch. The time duration of N cycles is to be measured and divided by N to get the average wave period. Whether the wave length **** is determined by visual observation, or by reading the mean distance between successive wave crests on the radar, T can be calculated by the following equation: T= 0.8***** 4.
TE:
measure this by timing a ship motion, such as pitching, on stop watch
.5 TR Measure the period of rolling motions, preferably when the ship is in a calm sea. this value is roughly estimated by the following equation:TR =2CB /GM Where: C=0.373+0.023(B/d)-0.043(L/100), Or by equivalent determination of coefficient C. Measurement or estimation of natural rolling period
The natural rolling period of a ship depends on the loading condition of the ship. Therefore, it is desirable to measure the ship’s natural rolling period in a calm sea on every occasion of departure after cargo loading or unloading. A stop watch can be used for the measurement. Measurement of wave period and observation of wave direction
The wave period is measured by a stop watch, and the wave direction is estimated by visual observation or by watching the radar image. The practice of wave and wind observation is common for the shipmaster of selected ships (world Meteorological Organisation (WMO). Preparations for heavy weather Verify vessels’ position investigate safe port option. Obtain up-to-date weather forecasts and expected weather conditions for surrounding areas.
SHIP HANDLING NOTES FOR PHASE II Warn all departments of impending heavy weathers. Rig lifelines fore and aft. Check: - Anchors and securing cover/ cement hawse / spurring Life boats and lashings Watertight doors closed General cargo stowage, securing and deck Cargo lashings . Close up ventilation, remove cowls and plug where app. Check stability no slack tanks, run up tanks if reqd Note preparations in log book. Contact shore, give position and obtain continuous plotting of storm’s track. Secure derricks, cranes and hatch covers Clear surplus gear from decks. Close down deadlights Slacken off signal halyards and other relevant cordage. Drain swimming pool Reduce manpower on deck, operate heavy weather routine. Take down awnings. Secure bridge for excessive pitching and rolling motion Warn engine room in plenty of time to reduce rpm. Check distress rockets and L.S.A. gear. Organise meal relief’s before set of bas weather . Clear scuppers and freeing “Port” Additional lashings on accommodation lrdders. Prepare oil for moderating the effects of sea. Heavy weather DO’s Be continually informed of expected weather changes Improve stability before encountering heavy weather. Ensure ship is seaworthy before leaving port and before onset of bad weather. Consider effect of ship’s motions on other crew members. Recognise approach of tropical storms and avoid them. Alter course to avoid synchronism in beam sea. DON’T’S Don’t drive ship too fast into head sea Don’t fail to reduce speed soon enough in head sea and swell. Don’t run too fast before a following sea particularly when length of sea is about the same as length of ship.
Pooping Occurs when A ship is on the forward slope of a wave or A ship falls into a trouc and does not rise with the wave. Or A ship falls on a rising wave. And a wave breaks on to the ship. A large amount of water is shipped over the stern and poop deck area can cause considerable damage.
SHIP HANDLING NOTES FOR PHASE II Heaving to Is the action of manoeuvring a ship in a manner so as to ride out a storm in the mostcomfortable position; avoid damage or capsizing. It is resorted to when continuing the voyage endangers safety of ship, its crew and cargo. Objectives of heaving to: Keep ship as steady as possible Prevent seas breaking onboard Prevent foundering, flooding and capsizing. Methods In coastal waters lie to the leeward side of some land mass. In open seas Sea on the bow Actions Reduce RPM to just sufficient to maintain steerage way. Maintain sea/wind on the bow (port bow if possible) so as to keep ship as steady as possible and any drift to leeward is away from land/shallow water/underwater hazards. Characteristics Vessel makes little headway over ground Heavy pitching and pounding may occur Likely structural damage forward to ships with wide flared bows. Most suitable where there is little room to the leeward. Sea on the quarter: Action Reduce speed to minimum rpm necessary to maintain steerage way and prevent being pooped or broached to maintain sea/wind on quarter at an angle where ship is steady. Characteristics Considerable drift to the leeward Steering will be difficult with considerably yawing Recommended When a ship has plenty of room to the leeward and good steering qualities at low speeds. Drifting with engines stopped Characteristics:Considerable drift to the leeward No steerage way Heavy rolling and pitching with risk of synchronisation and cargo shifting. Head to sea (wind and sea fine on the bow) Most favoured for deep draft vessels Has minimum drift to leeward. Dangers:Slamming of fore foot Violent pitching Continual pounding and considerable structural punishment.
SHIP HANDLING NOTES FOR PHASE II Racing of propellers; strain on engines Shipping of water. Actions Reduce speed to increase PE and reduce pounding ensure steerage way; avoid zone of critical revs. Stop engines on approach of extremely heavy seas. Use two steering gear motors. Adjust courses and speed to minimise hogging/sagging stresses and synchronism. Ensure slight trim by the stern. Sea abeam To be avoided as far as possible Dangers Excessive drift to leeward Heavy rolling and racking stresses Actions Alter course to reduce amplitude of rolling Make allowance for lee drift Use storm oil on weather side. Stern to sea (wind and sea on quarter) Dangers:Difficulty in steering and development of alarming yaw. Pooping Broaching to • • • •
Actions:- Reduce speed to about 40% CF wave velocity. Lee shore A shore towards whch strong wind is blowing •
Strong wind :Causes a ship to drift to the leeward; max when it is abeam to the wind and also. Creates a surface drift current if it blows with consistant force and direction over an area for 24 hrs or more. Rate can be upto: 2% of wind velocity in high latitudes (daily drift (M) appx wind velocity (knots)) 24% of wind velocity in low latitudes (daily drift (M) appx wind velocity (knots)) (Exceptions: Indian ocean in S.W monsoons. Daily drifts upto 160 miles) A light draft/low powered ship can be driven on to a lee shore. Handling ship to avoid drift onto lee shore:Swing the ship head to wind by rapid use of sea anchor. Let go both anchors when in suitable depths, snub bows head to wind and steam out to the windward weighing anchors on the way. 0 Wearing turn – turn through 270 downwind under full speed and helm until vessel heads the wind. Danger if ship fails to complete turn, it will be closer to shore. Flooding (for midships accommodation vessels) Reverse engines sufficient as to point stern into wind with minimum sternway. Flood after compartments rapidly by all possible means i.e. hoses, bilge lines (remove N/R valves), through D.B tanks not carrying oil (remove manhole covers) Ensuring minimum free surface effect. Avoid awkward trim by the stern. • •
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Remove all lose timber and gear to tween Dk, if time permits Turn into wind with full helm (preferably to port) Use oil to prevent breaking seas while going astern and flooding.
Recommended For low powered vessels unable to keep wind on the bow. In or near the centre of tropical storms Where sea room to the leeward is sufficient When the ship has adequate stability and good watertight integrity. • • • •
Turning a ship in heavy weather Warn catering and engine room departments. Observe waves and estimate pattern of rough and calm cycles. • •
Turning downwind Commence turn so as to experience relative clam period when the vessel is in the trough and commencing last half of the turn. Reduce speed to minimum During first half of turn use bursts of full ahead Use full power during the second half to compete the turn quickly. Reduce speed as necessary after competing the turn. •
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Turning up wind Commence turn so as to experience the relative calm during the latter half of the turn. Reduce rpm to minimum necessary for steerage Complete turn quickly, use bursts of full power. Use full power to bring bows into the wind. Reduce engine power as necessary. Admirality commence turn in period of re. Calm. • • • • •
Use of storm oil Strom oil reduces crest forming tendencies of waves It reduces breaking tendencies of wave crests Shipping of sea is lessened It has no effect upon swell. Low viscosity animal, vegetable or fish oils are ideal Lubricating oils may be used if above are not available. Fuel oil should not be used harmful to survivors in water if vessel has to be abandoned. • • • •
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Methods of distribution Oil should be discharged slowly above water level in any of the following manners:Filling an old punctured hose with oil, sealing both ends and trailing it overside horizontally, Large weighted canvas bags filled loosely with oil, oakum/cotton waste sealed and trailed overside. 5-10 ltr tin punctured at the base, filled with oil and placed into a wash basin or bath tub and oil flushed through soil pipes. Rate of discharge 7-8 litres per hour 200 ltrs of lub oil discharged slowly while steaming at slow 2 speed will reduce breaking seas over an area of appx 4500m • •
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Where to distribute oil Running before the sea/quarterly wind-from aft or from bows protects from quarterly seas in the event of yawing. •
SHIP HANDLING NOTES FOR PHASE II • • •
Running with wind and sea ahead-from the bows. Wind/sea abeam or drifting from weather side at intervals of 15 metres. At anchor oil bag hauled out ahead of the ship by means of a messenger rove through at dd block hitched to the cable.
Handling disabled vessels A disabled ship will lie with the wind and the sea abeam with dangers of:Drift to the leeward; Heavy rolling which may become synchronous Structural damage; Cargo shifting, and Capsizing • • • • • •
Action
Bring vessel head to wind by creating a drag forward Use storm oil to minimise wave breaking. Methods In anchoring depths trails a length of anchor chain along the sea bed Lash weather anchor in the hawse pipe; Detach anchor chain from anchor; Manhandle end of chain through forward fairlead (preferably panama fairlead); Pay out 3 or more shackles Use 2nd anchor chain only if 1 proves inadequate. Second anchor shoud be kept rea dy for use in an emergency. In all depths Lower one or both anchors to a maximum possible depth (without touching sea bed) Stream out on a wire hawser:Several empty drums rigged in a cluster An empty container A wooden raft weighted at its lower end with spare chains Wooden cargo slab hatch i.e. 5 or 6 wooden hatches strapped together with steel slats into a rectangle about 2.5M2 and weighted at its lower end. Several cargo baskets lashed to the hawser. Stream a triangular prism hatch tent, its apex removed and base stretched open with 2 crossed awning spars. (life of the sea anchor will depend on the strength of the spars). Fill a lifeboat with water and stream it ahead Rig up a makeshift mizzen sail • •
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