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Ships and Offshore Structures

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Computer and experimental simulations on the fineffect on ship resistance

B. Rajesh Regu Ram, S. Surendran & S.K. Lee

To cite this article: B. Rajesh Regu Ram, S. Surendran & S.K. Lee (2015) Computer andexperimental simulations on the fin effect on ship resistance, Ships and Offshore Structures, 10:2,122-131, DOI: 10.1080/17445302.2014.918308

To link to this article: http://dx.doi.org/10.1080/17445302.2014.918308

Published online: 19 May 2014.

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Ships and Offshore Structures, 2015Vol. 10, No. 2, 122–131, http://dx.doi.org/10.1080/17445302.2014.918308

Computer and experimental simulations on the fin effect on ship resistance

B. Rajesh Regu Rama, S. Surendrana,∗ and S.K. Leeb

aDepartment of Ocean Engineering, Indian Institute of Technology Madras, Chennai, India; bDepartment of NavalArchitecture and Ocean Engineering, Pusan National University, South Korea

(Received 11 July 2013; accepted 23 April 2014)

Container ships move at a higher speed compared to other merchant ship types. A fin attached to the ship hull proves tobe more efficient in controlling the moving ship. However, such attachments on the naked hull attract additional problemssuch as slamming, requirement of continuous maintenance, etc. The main objective of this study is to find the influenceof fin action at various angles of attack with the incoming flow and recommend the best possible fin position for the leastresistance. While experiments were performed for different angles of attacks of the fin with respect to the flow, a reduction inresistance was observed for an Fn range of 0.13–0.26. The fin was fitted at the lowest possible location of the hull surface atthe bow part of the ship. Experimental investigation was done using model tests in a towing tank to determine the resistanceof a scaled down model and it was compared with computer simulation. The interaction of a bow fin fitted to a container shipwith its own generated and encountering waves are discussed in this paper. It was observed that at certain angles of attack ofthe fins favourable resistance characteristics were observed. Modifications from the expected resistance due to fin effect arepaid attention in this study. Various resistance values for different angles of attack of the fin were compared and an angle ofattack of 5◦ is found to be the best.

Keywords: ship resistance; fin system; pitch reduction; computer simulation; towing tank

1. Introduction

The performance quality of a marine vehicle gets degradedin irregular sea due to an increase in ship response. It is wellknown that such a situation may lead to adverse workingconditions and may result in cargo loss, structural damage,etc. Fin systems were successfully used in the past to countersuch effects, to a certain extent, due to ship motions (Kaplanet al. 1984). Such systems have been additional concernsto the master and engineers in view of maintenance andoperation. However, in certain situations the resistance ofthe vessel is found reduced due to modifications of the ship-generated waves. The ship wave systems are complicateddue to the presence of pressure points such as a bulbousbow and points of shape change along the streamlined hull.The main aim of this paper is to arrive at the modificationsin favour of ship resistance due to fin systems. The finstabilisation consists of a pair of fins fitted roughly nearthe bow region of the ship. It should be as far as possiblefrom the longitudinal centre of floatation (LCF) to developmaximum possible moment by the immersed fin. The finmoment is supposed to counter the external moment causedin the forward motion. The flow around a hydrofoil sectionof the fin causes lift which is a function of aspect ratio andangle of attack of the flow. However, the close proximity ofthe fin with the fixed hull makes the flow three dimensionalby doubling the effective aspect ratio of the fin. This is due to

∗Corresponding author. Email: sur@iitm.ac.in

the cross flow developed at the junction where the fin is closeto the fixed large hull surface. Such phenomena are alsoobserved during the experiment, and computer simulationshave been conducted for this investigation. A symmetrichydrofoil section (NACA 0018) is selected for the fin. Thespan of the fin is less than the maximum half breadth of thedesigned ship. The chord, which is related to the aspect ratioof the fin, is selected based on the anti-pitching momentrequired to control the motion. This will vary from ship toship and will depend on the fin angles possible within theship frame.

The fin should not project out of frame of the ship.The maximum span possible of the fin will be half the shipbreath. The maximum span of the fin can be fixed. The ratioof the area of the fin to the area of load water line should be4.6%. The aspect ratio and span are shown in the relevanttable. Now the total moment required to control the motionwill depend on the lift force generated by the fin and thedistance from LCF. Out of this the lift force is the onlyparameter which can be varied by the fin design. The liftforce depends upon the fin area and hence for the requiredlift the chord is selected. Further fin details are provided inthe following sections.

Abkowitz (1959) stated that the loss of speed due to thefin was not excessive in calm water and the fixed fin couldbe designed, thus reducing resistance for a certain speed.

C© 2014 Taylor & Francis

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Ships and Offshore Structures 123

Stefun (1959) conducted experimental investigation onanti-pitching fins. Heave and pitch motions for differentaspect ratios and angles were studied and the possibilityof a speed reduction in waves also explored. Becket andDuffy (1959) stated that bow fins experienced ventilationand cavitations which led to excessive vibration when bub-bles collapsed on the fin and the hull. Ochi (1961) focussedon ships fitted with bow and stern fins. The author reportedthat there was an increase in resistance of stern fins of twoto three times that of bow fins. With bow a 10% reductionin pitch was achieved. Bhattacharyya (1978) worked outpitch motion reduction using fins fitted to underwater hull.The fin was fixed as low as possible to the ship’s bow, asthe emergence of fin caused serious operational problem.Slamming-like forces are possible during the emergence ofthe fin and this must be considered in the structural design.The fin used for pitch stabilisation was a hydrofoil sectioncantilevered to the hull surface in the bow of the ship. Thefin is designed in such a way that the area of the fin isroughly 4.6% of the area of the load water line. Kaplanet al. (1984) studied the problem of pitch stabilisation tocommercial and military craft with stern and bow fin. Thestern fins are less effective than the bow fin even when itis active. Avis (1991) studied the use of anti-pitching fin toreduce the added resistance of a yacht in waves. The authorproposed a mathematical model to predict the effect of anti-pitching fin on ship motion and added resistance. The authorvalidated his results with experimental investigation whichclaimed 22% reduction in pitch, 15% reduction in heave and40% reduction in added resistance. This appeared to be aninteresting observation. Kuniaki et al. (2005) fitted wedge-shaped active fins onto ship bottom to study the reduction

Table 1. Vessel and model particulars.

Particulars Full scale Model (1:100)

LBP 313.64 m 3136.4 mmB 36.64 m 366.4 mmDepth 24.1 24.1 mmDraught 14.5 m 145 mmDisplacement (mass) 106235.38 tonne 103.29 kgL/B 8.56 8.56B/T 2.53 2.53Cb 0.622 0.622Kyy/Lpp 0.27 0.27

in ship hull resistance. The authors arrived at the fact thatthe fins were effective in reducing resistance in the high-speed zone of motions. Perez (2005) discussed fin actionto control ship motion with roll stabilisation and combinedrudder–fin stabilisers. The author discussed many spin-offuses of activated fins.

2. Vessel and model particulars

A post-Panamax containership is taken for study and ascaled down model (1:100) is fabricated using fibre rein-forced plastic for experimental investigation. The generalparticulars of the ship and the model are shown in Table 1.Body plan has been shown in Figure 1.

2.1. Fin details

A symmetrical hydrofoil section is chosen for the fin model.Figure 2 shows the three-dimensional view of the fin. Threeaspect ratios are considered for study and the same has been

Figure 1. Body plan of the container ship.

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Figure 2. Three-dimensional view of the fin.

Table 2. Fin particulars.

Span (m) Chord (m) Aspect ratio

8 15.9 0.510 15.0 0.6312 15.9 0.75

tested for their effectiveness. The span of the fin is selectedin such a way that the fin does not project out of the ship’shull frame. The fin aspect ratio is shown in Table 2. Threeaspect ratios are for varying the span of the fin pairs to seethe effect on the resistance. The vessel is modelled usinga proven computer package program. The service speed of25 knots is taken for analysis. Such a higher speed is chosenfor academic interest, although the actual speed may bebelow this value. Fin systems are known to be effective inhigher speeds. A trend is observed to operate such vesselaround 20 knots; here higher speeds are considered for thereasons already stated.

Figure 3 shows the profile of the ship with the fin. Thefin is fitted close to the hull surface to form an integral partof the ship so as to generate a three-dimensional flow aroundthe hull surface and this doubles the geometric aspect ratio

of the fin. This will increase the effectiveness of the fin bycreating more lift for smaller deflection. The fin encounterswaves with a forward velocity in addition to this the waterparticle velocity.

2.2. Computer simulation for fin action

The effectiveness of the stabilisation depends upon the finlocation, the fin angle and the fin aspect ratio. Figure 4shows the plan view of the fin system in the bow part. Thelevel is where the fin shaft is fitted through the hull. Figure 5shows the ship’s coordinate system. A meshed model of thehull surface is prepared and simulations are done using thecomputer package.

The ships wave pattern around the hull is captured andshown in Figures 6 and 7. A clear distinction between thewaves system is visible from the figures. Fin angles of 5◦,10◦ and 15◦ are considered for the simulation.

The simulation is performed for speed interval of5 knots. However, only 5 knots speed and 25 knots speedare shown in the figures. It is understood from various simu-lations under different conditions that the creation of wavesrequires energy. As the ship speed increases, the wave heightproduced by the ship increases. Hence, the energy requiredto produce this wave also increases. The energy expendedby the ship to create and maintain these waves represents en-ergy that could have been used to make ship go faster. Thiswave-making resistance is modified by the presence of thefin which in its newly deflected position created additionalpressure pulse responsible for the alteration of wave systemaround the wetted hull. As already mentioned, fins fitted inthe forward part are meant to modify the pitch angles of theship. In some conditions, the total resistance can be greaterand in other conditions it can be smaller. Although exten-sive study is required to establish a theory in this regard,the results achieved were interesting for fin designers. The

Figure 3. Profile showing bow part with the fin. (This figure is available in colour online.)

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Figure 4. Plan view of the bow part with the fin showing different aspect ratios. (This figure is available in colour online.)

Figure 5. Ship coordinate system.

Figure 6. (a) Free surface wave pattern without fin at 5 knots.(b) Free surface wave pattern with 5◦ fin angle at 5 knots. (Thisfigure is available in colour online.)

results obtained using limited experiments were comparedwith that achieved using simulations. Figures 6a and 6bshow the wave pattern for a speed of 5 knots without andwith fin, respectively. The simulation shows that at 5◦ finangle the fin effect is more predominant; hence, a 5◦ finangle is taken into account for detailed study.

The fin was deflected upwards by the leading edge. Thewave elevation on the free surface at the position of thefin location shows the fin force acting at that point causinga different elevation than that of the ship without fin. Inall these figures with the use of fins, there is a furtherinteraction of fin system with the other wave patterns. Thefin acts as additional pressure points which interfere withthe ship wave pattern. A number of speeds were selectedfor such computer simulation. A gradual change in thewave pattern is observed in each case. Only one low speedand a higher speed are discussed through Figures 6 and 7,respectively. Figures 7a and 7b are for 25 knots of speed. Aclose observation of wave-making phenomena is presentedin the next section.

2.3. Fin effect on ship wave elevation

A meshing is done in the domain around the ship to locatethe wave elevation due to additional pressure by tilted fin.

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Figure 7. (a) Free surface wave pattern without fin at 25 knots.(b) Free surface wave pattern with 5◦ fin angle at 25 knots. (Thisfigure is available in colour online.)

Figure 8. Grid position for showing wave profiles along longitu-dinal and transverse directions. (This figure is available in colouronline.)

Conventional coordinates forming x–y–z frames are con-sidered. In the horizontal plane, the domain is divided intoa number of meshes as shown in Figure 8. The elevations ofcombined waves in x–z and y–z planes are discussed here.

Table 3 shows the grid details. The ship has its own wavesystem. The presence of the fin alters the pressure aroundit and it interferes with the otherwise existing wave system.The viscous resistance will be more or less the same for acertain speed. If at all there is a change in resistance, its mainreason will be the additional pressure due to fin, modifyingthe ship-generated waves without fin around the hull. Thecrests and troughs of waves observed are studied in detailfor a maximum speed of 25 knots. The leading edge of thefin was tilted upwards for an angle of 5◦. Figure 9 showsthe meshed model prepared for computer simulation.

Table 3. Grid details.

Sl. no Description Particulars

1 Transverse grid points 100 (one side taken inview of symmetry)

2 Longitudinal grid points 2003 Distance forward of ship

(in terms of vessel length)1

4 Distance aft of ship (interms of vessel length)

4

5 Distance side of ship (interms of vessel length)

2

The ship’s draft is taken as 14.5 m. At some speeds it wasseen that crests and troughs reinforced each other producinghigher waves, but then the fin also played a role either toassist or to negate this effect. The net wave elevation whilepropagating along the transverse grid, i.e. in the y–z plane, iscaptured from the simulation. The net wave at forward partof the ship, leading edge of the fin, mid of the fin and trailingin head sea at 25 knots is taken for study. Wave elevationfor various positions like bow part, leading edge of fin,trailing edge of fin and bulbous bow region are determinedand only two cases are shown in Figures 10 and 11. Atlower angles like 5◦ tilt of the fin, an advantage on the totalresistance was seen. If Figures 10 and 11 are compared, thisfact is cleared to the reader. The bow part wave is shown inFigure 10 and a larger hump is seen without the fin effect.In the same figure a crest is seen as the effect of deflectedfin. The difference in the phase causes reduction in thewave amplitude, thereby reducing the encountering waveamplitude. The wave elevation is non-dimensionalised withthe ship draft and the lateral distance from the ship’s centreline is non-dimensionalised with the breadth of the ship.The combined wave profile beginning from outer hull linepropagating along the y-direction up to roughly 200 m alongthe breadth of the ship is shown in Figures 12–14. Thesewave profiles are captured from the simulations while theymove along the length of the ship. The fin with maximumaspect ratio is considered for the simulations. Here, thedivergent waves and transverse waves are combined to forma new wave system with the presence of the fin. The figuresare shown in a background of y–z or parallel to y–z plane.

The next section deals with the wave profile projectedon the x–z plane starting from the immediate outer planeof the hull represented by y = B/2, where B is the totalbreadth of the ship. This plane is also similar to a planeparallel to that of buttock lines of the ship. Figure 12 showsthe wave profile due to the fin and in the absence of thefin. At a plane parallel to x–z and at y = B/2 + 6.33 meither port or starboard, the wave profile will be as shownin Figure 13. The forward perpendicular (FP) and aft-mostpositions can easily be understood from the figure. Thex-axis shown is non-dimensionalised with the ship length

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Figure 9. Meshed model with 5◦ fin angle. (This figure is available in colour online.)

Figure 10. Combined wave pattern at leading edge of fin at25 knots projected on y–z plane. (This figure is available in colouronline.)

Figure 11. Combined wave pattern at trailing edge of fin at25 knots projected on y–z plane. (This figure is available in colouronline.)

and y-axis is the non-dimensional wave elevation whichis wave elevation divided by the draft. Figure 13 showsthe influence of the fin in creating wave pattern of withsignificant humps and hollows. Strong humps and hollowsare seen in these figures. The forward position FP of theship can easily be located in the figures. Figure 14 is the

Figure 12. Wave profile on a plane tangential to the outermosthull line parallel to x–z plane. (This figure is available in colouronline.)

Figure 13. Wave profile on a plane at 6.33 m away from outerhull parallel to x–z plane. (This figure is available in colour online.)

wave profile in the vertical plane defined by y = B/2 +12.67 m.

A number of wave profiles are obtained on the longitu-dinal and transverse planes as outputs and all show a stronginfluence of the fin at its tilted conditions. The most rep-resentative figures are shown here to optimise space. Allthese figures show that the ship-created wave profiles are

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Figure 14. Wave profile on a plane at 12.66 m away from outerhull parallel to x–z plane. (This figure is available in colour online.)

comparable to that generated by the fins, meaning that thefin system has a significant effect on the ship resistance.The interaction happens in such a way that the net resis-tance may be reduced in some conditions of operations.The flow around the fin modifies the wave system formingthe surface profile above at the air water interface. The am-biguity of wave-making resistance, if any, can be overriddenby conducting experiments in a towing tank.

3. Experimental setup

The experimental setup is divided into two parts: one com-prises fabricating the hydrofoil section using fiber rein-forced plastic (FRP) and the other is setting up the me-chanical setup to activate the fins. The fins are fitted to themodel using a special mechanical setup fabricated locallyto counter the wave load. The vibration is damped due tothe surrounding fluid media. The perturbation of the me-chanical setup through the model surface is prevented fromwater leak by using water seals. The angular displacementto the fin is provided with the help of a centre link rod whichis fixed within the ship model.

3.1. Fabrication of hydrofoil fin

The fabrication process consists of pattern making and splitmoulding by hand layup method. The pattern is made inwood in a precise manner with smoothness as per the co-ordinates of the hydrofoil section and aspect ratio. Thewooden patterns are made for three different aspect ra-tios, so that a study of aspect ratio on fin effect can bedone. From the pattern, a split mould is made using fibre-reinforced plastic. The hydrofoil-shaped product is takenfrom the mould and is stiffened using stainless steel framesto take the hydrodynamic load.

3.2. Fabrication of mechanical system

The mechanical setup holds the fin in position and it takesthe hydrodynamic load exerted on the fin. The setup is

Figure 15. Angle gauge for angular motion. (This figure isavailable in colour online.)

designed in such a way that the fin is aligned in its positionon both sides of the model surface, as shown in Figure 15.Figure 16 shows the position of the tilt angle of the fin.Provision is given in the setup to change the fin angle bymeans of a link rod. The operator standing on the towingcarriage can change the angle of the fin using this lever. Thesetup consists of an outer hollow shaft, an inner solid rod,and a side sleeve which lies between the hollow shaft andthe inner rod. Water seal is to prevent ingress of water intothe ship model. Bores are provided at the centre of the innerrod and slots are taken in the centre of the hollow shaft. Therod is positioned in such a way that the bore exactly matchesthe slot in the hollow shaft. A link rod is attached to thebore in the inner rod by which the inner rod can be activatedmanually. The hollow shaft is fixed firmly to the model hull,thereby restricting the movement of the shaft. A calibratedangular gauge to fix the link rod at desired angle is attachedon the outer shaft whereby we can measure the fin angle bymoving the link rod. Holes are driven on the outer shaft torestrict the motion of the inner shaft, once the desired thefin angle is setup by the link rod. This is achieved by drivingspecial screws through the outer shaft and these will reston the inner rod. A locking assembly is provided to makethe system more rigid by connecting the linking rod and the

Figure 16. Inner-connecting rod for tilting the fin. (This figureis available in colour online.)

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Figure 17. Mechanical setup fixed on the ship. (This figure isavailable in colour online.)

calibrated system by means of interconnector. The fin afterturning to the required angle can be fixed at that positionusing studs in the slots. Figure 17 shows the mechanismfitted inside the model and Figure 18 shows manually fixingof fin angle using the tilting mechanism. The experimentalsetup and mechanical hardware were achieved using manyhours of skilled manpower, after carefully planning anddesigning the components.

4. Towing tank test

A high-speed towing tank was utilised to test the ship model.The ship model with fin is attached to the towing tankcarriage and it is pivoted at the forward and aft by means ofa mechanical lock which controls the surge motion of themodel and it allows the model to pitch and trim. Figures 19and 20 show the model in the tank without and with fin,respectively.

4.1. Effect of fin on ships resistance

The resistance has been done following the InternationalTowing Tank Conference (ITTC) standards for Froude

Figure 18. Manual fin angle tilting mechanism to change finangle. (This figure is available in colour online.)

Figure 19. Model without fin in towing tank. (This figure isavailable in colour online.)

number ranging from Fn = 0.05 to Fn = 0.26. Repeatedruns were done for chosen Froude numbers. The totalmodel resistance was measured by using a dynamometer.Trim is measured for the same Froude numbers by meansof a set of accelerometer fitted on the forward and aft ofthe model. The test is carried out with the model for evenkeel condition. Resistance and trim of the model with andwithout fin are measured. The resistance with the carriagespeed for model without and with fin at 5◦ and 10◦ wasnoted from the data acquisition system.

4.2. Ship resistance calculation by extrapolation

Ship resistance consisted of mainly wave-making andviscous pressure plus eddy making, air resistance, etc.Some packages based on potential flow concept givespecial modules to deal with boundary layer in flat plate,its form effect and associated viscous components. For ahull, there are many components of wave-making parts.A bow wave system, fore shoulder system, aft shouldersystem and stern system are superposed on a symmetricaldisturbance. This has been discussed by Lewis (1990).There are interference effects with all these componentsand with the presence of the fin the matter becomes abit more complicated. The ship’s resistance is calculatedbased on the Holtrop’s (1984) method; it is usually meant

Figure 20. Model with fin in towing tank. (This figure is availablein colour online.)

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Table 4. Limiting criteria for Holtrop’s resistance predictionmethod.

Ship parameters Holtrop limitation Container ship

Cp 0.55–0.85 0.673L/B 3.9–15 8.54B/T 2.1–4 2.53

for high-speed vessels. The total resistance of ship consistsof various components and is given by

Rtotal = RF (1 + K1) + RAPP + Rw + RB + RT R + RA,

(1)

where RF is the frictional resistance according to theITTC-1957 formula, (1 + K1) is the form factor describingthe viscous resistance, RAPP is the resistance due toappendages, Rw is the wave-making and wave-breakingresistance, RB is the additional pressure resistance ofbulbous bow near the water surface, RTR is the additionalpressure resistance of immersed transom stern and RA

is model–ship correlation resistance. The value of K1

for the container ship was taken as 0.145. The resistanceprediction algorithm as per well-known Holtrop’s methodhas its limitation and it is shown in Table 4.

Resistance, for various speeds translated into Froudenumbers, was determined and is used in Figure 21. Initialtowing was done for bare hull. After covering all sets oftows without the fin system, the hull model was fitted withfins on sides. Towings were done in the tank for the selectedspeeds. In the first case the fin was tilted 5◦ up at the noseof the fin. After covering all speeds, the fins were tilted10◦ up. The readings of speed and resistance were noted.The experiment shows the highest resistance with the finangle tilted up to 10◦. It is obvious that such an angle offin will create its own drag and will offer higher resistance.At the same time, the computer simulation shows a lesser

Figure 21. Comparison of resistance values using computerand experimental simulations. (This figure is available in colouronline.)

value of resistance. For a lower angle of tilt, it could havegiven a realistically better result. For a 5◦ tilt case, thecomputer simulation gives very low resistance. The samewith the experiment is also found to be of lower values. Thistrend shows that the computer simulation underpredicts theresistance values and the experiment can be taken as abenchmark for further investigation. The resistance can bebrought down using a finer angle of tilt of the fins.

4.3. Observations and discussions

Observation has been done taking the projection of wavesonto y–z and x–z planes. The x–z plane will give the eleva-tion of waves created with the fin turned to an angle and alsowithout a fin. The ship generated waves have their crests andtroughs with respect to the mean vessel draft of 14.5 m. Thetrend of divergent waves and transverse wave elevations areshown in figures. Significant influence of fin is seen in therelevant figures. In the presence of a fin in its tilted condi-tions, there is strong interaction among many componentsof the wave-making resistance. The maximum wave eleva-tion for the ship without fin is 0.55 m above load water orstill water line and that for the ship with fin is 0.92 m. At theregion of the fin, the divergent wave pattern changes. Thefin in the bow part of the ship causes a wave crest insteadof wave trough as in the case of ship without fin.

In the transverse wave pattern shown against x–z plane,the zero reference point in plot shows the aft-most part ofthe ship. From the plot it is seen that at far forward of theship there is no wave elevation. At the forward part of theship the wave elevation is greater for ship with fin. This isdue to the pressure generated due to the fin. As the wavetravels along the length of the body it interacts with theshoulder waves and its magnitude increases. This regionof the wave acts on the ships parallel middle body whichdoes not contribute towards resistance. As it moves further,the magnitude decreases but it is greater than that of theship without fin. At the aft part, the pressure componentsupporting the motion is higher in the case of ship with finas the wave elevation in the aft is higher. The net effect ofthe transverse and the longitudinal wave due to the fin arethe reduction in the ship resistance.

Experiment shows that for fin angle of 5◦ there is areduction in ship resistance than that of the ship without finand with 10◦ fin angle. The resistance is represented in anon-dimensional form. The model resistance with fin at anangle of 5◦ is less than the resistance of the model withoutfin and with fin at an angle of 10◦. The lift force generatedby the fin at an angle of 5◦ produces trim aft to the model,thereby reducing the wetted surface area of the model. For10◦ fin angle the drag force will be greater compared to thatof 5◦ angle; hence, there is an increase in the resistance.The flow around the fin got an influence in reducing theresistance at an angle of tilt of 5◦. Slight trim was observedduring the tests for higher tilt angles of the fin system.

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5. Summary and conclusions

Study on fin effect on container ship shows consider-able modification in wave-making resistance which mightcause a reduction in ships resistance. At lower Froude num-ber the wave-making phenomenon is less and more reduc-tion in resistance is found at higher Froude number. Athigher Froude number, the interaction between the ship-generated waves and the fin-generated waves reduces thewave-making effect on the ship hull surface. At its servicespeed with the fins, a considerable reduction in its resistanceis achieved. An angle of tilt of 5◦ is found most effectiveto modify wave making and hence total resistance. The re-sults can be refined to finer values at the cost of time andbudget for utilising towing tank. Investigation of the fin ef-fect on resistance, mainly due to ship-generated waves, isperformed and the effect of added resistance due to fin isfound to be negligible. The pressure waves generated by thefin, the angle of attack of the fin with the flow and the inter-action of the fin-generated components with the rest of thewaves are responsible for a reduction in the total resistance.At higher speeds of wave making, such an interaction ispredominant. However, a higher angle of tilt of fin mightcause more resistance and sample case of 10◦ tilt was in-cluded in the study. A software approach underpredicts theresistance. The results of tank tests can be considered forfurther study by researchers. The results may be taken as abenchmark for approximations during conceptual and pre-liminary studies. An activated fin can be utilised in waves toobtain maximum reduction in resistance and ship motion.

AcknowledgementsThe first two authors would like to thank the Central Workshop ofIIT Madras for fabricating and machining the mechanical hard-ware for fin housing on the FRP hull. They are also thankful to the

scientists and technicians of the high-speed towing tank at NSTL,Visakhapatnam, India for conducting the tests. The authors recordtheir gratitude to Professor S.K. Bhattacharyya for suggestions atcritical stages of the study.

FundingThe second and third authors are thankful for the support of theMinistry of Science, ICT and Future Planning (MSIP) for the partof the paper completed in PNU, Korea.

ReferencesAbkowitz MA. 1959. The effect of antipitching fins on ship mo-

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