RESISTANCE AND POWERING ESTIMATION OF FISHING VESSELS AND TUGS.
CHARATERISTICS OF VESSELS HERE I AM GOING TO ESTIMATE THE RESISTANCE AND POWER OF FISHING VESSELS AND TUGS. THERE ARE TWO CATAGORIES OF VESSELS I AM GOING TO DEAL WITH. WE WILL FIRST DISCUSS THE FISHING VESSELS.
FISHING VESSELS: A fishing vessel is any ship or boat used to catch fish on seas, lakes or rivers. There are many different kinds of vessels used both in the fishing industry and in recreational fishing. Fishing vessels can be further divided into various sub-categories. Trawler is major types of fishing vessel.mainely commercial trawlers are used for fishing purposes. A commercial trawler is a commercial fishing vessel designed to operate fishing trawls. Trawling is a method of fishing that involves actively pulling a trawl through the water behind one or more trawlers. Trawls are fishing nets that are dragged along the bottom of the sea or in midwater at a specified depth. A trawler may also operate one or more trawl nets simultaneously (double-rig and multi-rig). There are many variants of trawling gear. They vary according to local traditions, bottom conditions, and how large and powerful the trawling boats are. A trawling boat can be a small open boat with only 30 hp or a large factory trawler with 10,000 hp. Trawl variants include beam trawls, large-opening midwater trawls, and large bottom trawls, such as "rock hoppers" that are rigged with heavy rubber wheels that let the net crawl over rocky bottom.
Side trawlers: Until the 1950s trawlers in the Atlantic Ocean were designed to shoot and haul trawl gear from the side.
Stern trawlers: From the 1950s, trawlers have been designed to operate gear from the stern. Technically, stern trawling is more feasible than side trawling and uses space more efficiently. It can be fully mechanized, enabling faster and safer operation of the gear, and better performance in heavy weather.
Factory trawlers: A factory trawler is a large stern trawler which has additional facilities for processing and freezing fish installed on board. This allows the factory trawler to stay for long periods at sea. Factory trawlers can displace up to 3,000 tons.
Wet trawlers: Wet trawlers are designed to make short fishing trips and land fresh fish kept in ice.
Sailing trawlers: Traditional sailing trawlers were limited to trawling at depths of 55-75 metres, but modern trawlers often trawl to 900 metres, with experiments having gone even deeper.
TUGBOATS: A tugboat, or tug, is a boat used to maneuver, primarily by towing or pushing, other vessels (see shipping) in harbours, over the open sea or through rivers and canals. They are also used to tow barges, disabled ships, or other equipment like towboats. Tugboats are quite strong for their size. Early tugboats had steam engines; today diesel engines are used. Tugboat engines typically produce 750 to 3000 horsepower (500 to 2000 kW), but larger boats (used in deep waters) can have power ratings up to 25 000 hp (20 000 kW) and usually have an extreme power:tonnage-ratio (normal cargo- and passenger ships have a P:T-ratio, kW:GRT, of 0.35-1.20, whereas large tugs typically are 2.20-4.50 and small harbour-tugs 4.0-9.5). The engines are often the same as those used in railroad engines, but typically drive the propeller mechanically instead of converting the engine output to power electric motors, as is common for railroad engines. For safety, tugboats' engines feature two of each critical part for redundancy. Tugboats are highly maneuverable and various propulsion systems have been developed to increase maneuverability and increase safety. The earliest tugs were fitted with paddle wheels but these were soon replaced by propeller-driven tugs. Kort nozzles have been added to increase thrust per kW / hp. This was followed by the nozzle-rudder which omitted the need for a conventional rudder. The cycloidal propeller was developed prior to World War II but was only occasionally used in tugs because of its manoeuvrability. After World War II it was also linked to safety due to the development of the Voith Water Tractor; a tugboat configuration which could not be pulled over by its tow. In the late 1950s the Zdrive or (azimuth thruster) were developed. Although sometimes referred to as the Schottel system many brands exist: Schottel, Z-Peller, Duckpeller, Thrustmaster, Ulstein, Wärtsilä etc. The propulsion system are used on tugboats designed for tasks such as ship docking and marine construction. Conventional propeller/rudder configurations are more efficient for port-to-port towing. The Kort nozzle is a sturdy cylindrical structure around a special propeller having minimum clearance between the propeller blades and the inner wall of the Kort nozzle. The thrust:power ratio is enhanced because the water approaches the propeller in a linear configuration and exits the nozzle the same way. The Kort nozzle is named after its inventor, but many brands exist.
Harbor tugs are the most typical of the tugboats that people recognize. They are used worldwide to move ships in and out of berth and to move industrial barges around waterfront business complexes. Their job has remained the same but their design and engineering has changed much over the decades. Harbor tugs have evolved from paddle wheelers, to the conventional tug known by all, and now to the Ship Docking Moduals and tractor tugs in the modern industry. River tugs are also referred to as towboats or pushboats. They are designed as large squared off vessels with flat bows for connecting with the rectangular stern of the barges. They are large and powerful, most commonly seen on the big rivers of the world. They are capable of pushing huge fleets of barges that are lashed together into "tows". Some tows can be up to 1000 feet long and 200 feet wide. Smaller push boats are often seen handling only a few barges on inland waters. Despite their size, they are designed to push their tow rather than tow from the stern. The conventional tug is the standard seagoing tugboat with a model bow that tows its payload on a hawser. A hawser is the nautical term for a long steel cable or large synthetic fiber rope. It operates independently and is used to tow various loads, e.g., cargo barges, ships, oil rigs, and etc. This is the most versatile method of towing since the conventional tugboat is able to move its load three ways: Pushing from behind, secured to the side of the towed vessel, or by towing astern, all achieved by the use of various lines and cables in various configurations. They are importantly recognized as the design of choice for salvage and assistance of wrecked ships and in the rescue and safe return of disabled ships from the high seas. The notch tug is a conventional tug which is assigned to tow and push a specific barge, usually built to the shape and specifications of that tugboat. A notch tug has a large towing winch on its stern but it gets its name from the deep notch
built into the stern of the barge. This notch is built in the exact shape of the tug's forward hull and can be quite deep, up to 90 feet, sometimes more. The tugboat fits snugly into the notch of the barge and with the use of various lines can be secured firmly enough to push the barge at much higher speeds than it would if it were towing. The towing hawser remains rigged during pushing. In the event that the seas get too rough to push safely, the tug merely releases any securing lines and backs out of the notch while extending its towing hawser. Once in calmer waters, the tug can maneuver back into the notch and resume pushing.
METHOD OF ESTIMATION OF RESISTANCE: Tugs and trawlers (fishing vessels) are small displacement type vessel. Estimation of resistance of this type of vessels is mainly done by 1. GULDHAMMER’S AND HARVALD’S METHOD The method was developed by guldhammer and harvald after which the method was named. The method uses a wide range of data of ship to determine the resistance and estimate power. Under following conditions this method can be applicable. 4.0 <= L/DISP^0.333 <= 8.0 0.5 <= Cp <= 0.8 -3 <= LCB % <= 3 2. VAN OORTHMERSEEN’S METHOD An analysis based upon work published by G. van Oortmerssen. It uses a wide range of parameters from which to calculate calm water resistance and Effective Horsepower of tugs and trawler forms in the Froude number range 0.1 - 0.5. There are following constrain for being applicable: 0.365<= Cb <=0.703 0.5<= Cp <=0.725 3.0<= L/B <=6.02 1.90<= B/T <=4.0 -8 %<= LCB <=2.8 % 0.1<= Fn <=0.5 Both of these methods can be used to estimate resistance and power required for fishing vessels and tugs.
Guldhammer’s and Harvald’s Method for Estimation of Resistance And Power First of all we need following parameters about the vessel: 1. Length between Perpendicular (Lbp) 2. Beam (B) 3. Draft (T) 4. Displacement (Disp) 5. Longitudinal Center of Buoyancy (LCB) 6. Working Speed (v) Now suppose we need to find resistance at particular velocity. STEP 1. Convert velocity from knots to m/s. Find the value of froude number at that speed (say v). Get the value of Lbp/Disp ^0.33 STEP 2. Now evaluate 10³CR for calculated froude number and Lbp/Disp^0.333 from given graph . Graph will be having different curves for different prismatic coefficient (Cp).so get value for the prismatic coefficient of given vessel. Interpolation can be done if required to find the value. Step 3. B/T correction The diagram have been made for a breadth-draught ratio corresponding B/T=2.5 A correction must be made if CR is desired for a ship with a larger or smaller B/T ratio. Correction formulae: 10³ CR = 10³ CR(B/T=2.5) + 0.16(B/T – 2.5) Correction may be positive or negative. Step 4. LCB Correction The 10³ CR curves are intended to correspond to vessel with a longitudinal position of center of buoyancy near to what is today considered the best possible position. the dependence of ship resistance on LCB is evident at higher speeds. Get the standard LCB from the given graph. If LCB is aft LCB standard no correction is required. But if it is not, then, get the value of ∂10³ CR /∂LCB at the calculated Froude number. Now corrected value is given by formulae 10³ CR = (10³ CR ) + ∂10³ CR /∂LCB * (|∆LCB|)
Step 5
Hull correction The resistance curve applies to a standard form ,that is the section are neither distinctly ‘U’ shaped nor ‘V’ shaped. Fore body extreme U = -0.1 extreme V= 0.1 Aft body extreme U = 0.1 extreme V= -0.1 This corrections cover speed range Fn=0.20-0.25,furthermore it must be considered standard form.
Step 6 Appendage correction Rudders – no correction. the standard form is intended to include rudder. Bilge keel – no correction Bossing – for full ship add 3-5% to CR Shaft brackets and shafts – for fine ships add 5 – 8% to CR. Step 7 Up to this step we have got the Residual Resistance Coefficient. (CR) Step 8 In this step we are going to find out the frictional resistance of the vessel. We will use ITTC formulae to find out the resistance of the vessel. CF = 0.075/(logRn – 2)² We need to find Reynolds number for it. Step 9 Incremental resistance It is the resistance due roughness and scaling effect For vessels with L <= 100 m =150 m = 200 m = 250 m >= 300 m
10³ CA = 0.4 = 0.2 =0 = -0.2 = -0.3
Air resistance and steering resistance can be omitted. Step 10 Now we have got all the resistance coefficient.so we are now ready to find the total resistance coefficient . Total resistance coefficient ,Ct Ct = Cr + Cf + Ca Total resistance is sum of all the resistance coefficients. Step 11 Now as we know the value of the total resistance coefficient we can now find the total resistance .
Rt = Ct * ½ * density(water) *wetted surface area* velocity^2 These is not the net resistance .to find the net resistance we have to add service condition allowance, depanding on the working zone of the fishing vessel. Service condition North Atlantic route ,eastward
North Atlantic route ,westward Pacific route South atlantic and Australian routes East Asiatic route
Allowance 15 – 20% in summer and winter respectively 20 – 30% in summer and winter respectively 15 – 30 % 12 – 18 % 15 – 20 %
After adding these allowance we get the net resistance Step 12 Power estimation As, now we know the net total resistance value we can calculate the power. Power = velocity * net total resistance
NUMERICAL EXAMPLE OF Guldhammer’s and Harvald’s METHOD FOR ESTIMATING RESISTANCE AND POWER: I have selected a fishing vessel ,of which I am going to estimate the resistance and power by method explained before. I am using fishing boat ‘Perintis’ designed by Universiti Teknologi Malaysia The body plan and particulars of the vessel is given below.
Body plan of fishing vessel ‘Perintis’
Principal particulars of fishing vessel ‘Perintis’ LBP 22.4 m Breadth 5.90 m Draught 1.80 m Displacement 92.62 tonne LCB 0.67 m aft amidship Wetted surface area 140.94 m^2 Cp 0.38 Cb 0.63 B/T 3.28 Speed 10.00 Knots
DIMENSIONS: LENGTH BETWEEN PERPENDICULARS(LBP) .√gL = 14.816 m/s BREADTH(B) DRAUGHT(T) DISPLACEMENT VOLUME ³√volume=4.487 m WETTED SURFACE AREA(S) 1/2*þ*S = 72231.75 N s^2/m^2
22.4 m 5.90 m 1.80 m 92.62 Tonnes 90.36 m^3 140.94 m^2
COEFFICIENTS: BREADTH - DRUGHT RATIO BLOCK COEFFICIENT PRISMATIC COEFFICIENT LENGTH - DISPLACEMENT RATIO LONGITUDNAL CNTER OF BUOYANCY SHAPE OF SECTION
B/T=3.28 Cb=0.38 Cp=0.63 4.99 0.67 aft amidship AFT: 'U' FRWD: 'V'
CONCLUSION: The resistance and propulsion of the fishing ship ‘ perintis ‘ has been calculated by guldhammer and harvald method. This method is very useful for fishing vessels, as the prediction by this method is very near to the actual value. This method can be widely used to find the resistance of fishing vessels and tugs. Estimation of resistance and power is mainly used to find out the engine requirements of the vessel. As we go through the graph of the froude number vs total resistance, we see that the resistance varies non linearly with froude number. the resistance of vessel increases with increase in froude number.( resistance due to fishing net is neglected). Also from the graph plotted, froude number vs power, is non-linearly increasing. We can see from the graph that the power required by vessel increases by a very huge amount with small variation in Froude number.
REFERANCES: 1. DESIGN OF MALAYSIAN FISHING VESSEL FOR MINIMUM RESISTANCE OMAR YAAKOB1, TEOH ENG LEE2, LIEW YEK WAI3, & KOH KHO KING4 2.
LEWIS , PRINCIPLE OF NAVAL ARCHITECTURE,VOL 2
