Speed reduction in waves

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i

HYDROMEGF1AN (CS o AERODYNAMIC o STRUCTURAL MECHAN ICS o APPLIED MATHEMATICS

SPEED REDUCTION IN WAVES

by

Margaret D. Bledsoe

HYDROMECHANICS LABORATORY RESEARCH AND DEVELOPMENT REPORT

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SPEED REDUCtION IN WAVES

by

Margaret D. Bledsoe

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TABLE OF COHTENTS Page ABSTRACT

i

INTRODUCTION

i

DESCRIPTION OF TESTS

i

DISCUSSION OF RESULTS 3 CONCLUSIONS 5

APPENDIX - EXPERIMENTAL SPEEDS OBTAINED FOR VARIOUS

TEST CONDITIONS 7

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Figure Figure Figure Figure

Figure 5 - Speed versus Wave Height for Constant Wave Length,

Destroyer Escort 15

Series 60, .0.60 Block Coefficient 15

Figure 7- Speed versus Wave Height for Constant Wave Length,

M/S SAN FRANCISW 16

Figure 8- Speed Reduction Curves for Destroyer Escort 16 Figure 9 . Speed Reduction Curves for Series 60, 0.60 Block Coefficient 17

Figure 10 - Speed Reduction Curves for M/S SAN FRANCISCO 17

Figure 11 - Critical Wave Length as a Function of Speed and Wave Height,

Destroyer Escort 18

Figure 12 . Critical Wave Length as a Function of Speed and Wave Height,

Series 60, 0.60 Block Coefficient 18

M/S SAN FRANCISCO 19

Figure 14- Speed Loss in Percent for Constant Wave Length with Thrust for

Design Speed in Still Water, Destroyer Escort 19

Figure 15 - Speed Loss in Percent for Constant Wave Length with Thrust for

Design Speed in Still Water, Series 60, 0.60 Block Coefficient 20

Figure 16 - Speed Loss in Percent for Constant Wave Length with Thrustfor

Design Speed in Still Water, M/S SAN FRANCISCO 20

Figure 17- Speed Loss in Percent for Constant Wave Length with Thrust for

Two-Thirds Design Speed in Still Water, Destroyer Escort 21 Figure 18 - Speed Loss in Percent for Constant Wave Length with Thrust for

Two-Thirds Design Speed in Still Water, Series 60,

0.60 Block Coefficient 21

Figure 19 - Speed Loss in Percent for Constant Wave Length with Thrust foc LIST OF ILLUSTRATIONS

Page

i - Body Plan for Destroyer Escort 12

2 - Body Plan for Series 60, 0.60 Block Coefficient 12

3 - Body Plan for M/S SAN FRANCISCO 13

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Figure

27 - Comparison of Speed Reduction of the Three Ships for h/L = 0.017 and Thrust for Design Speed in Still Water 28 - Comparison of Speed Reduction of the Three Ships for

h/L = 0.017 and Thrust for Two-Thirds Design Speed in Still Water 29 - Comparison of Speed Reduction of the Three Ships for

h/L 0.033 and Thrust for Design Speed in Still Water

31 - Comparison of Speed Reduction of the Three Ships for = 0.017 and Thrust for 14 Knots in Still Water

24 24 25 25 26 26 27 28 Page Figure 20 - Sneed Loss in Percent for Constant Wave Length with Thrust for

One-Third Design Speed in Still Water, Destroyer Escort 22 Figure 21 - Contours of Constant Speed Loss with Thrust for Design Speed,

Destroyer Escort 23

Figure 22 - Contours of Constant Speed Loss with Thrust for Two-Thirds

Design Speed, Destroyer Escort 23

Figure 23 - Contours of Constant Speed Loss with Thrust for Design Speed, Series 60, 0.60 Block Coefficient

24 - Contours of Constant Speed Loss with Thrust forTwo-Thirds Design Speed, Series 60, 0.60 Block Coefficient

25 - Contours of Constant Speed Loss with Thrust for DesignSpeed, M/S SAN FRANCISCO

Figure 26 - Contours of Constant Speed Loss with Thrust for Two-Thirds

Design Speed, M/S SAN FRANCISCO

Figure 30 - Comparison of Speed Reduction of the Three Ships for

h/L = 0.033 and Thrust for Two-Thirds Design Speed in Still Water 27

LIST OF TABLES

Table i - Characteristics of Ship Forms 2

Table 2 - Dimensionless Natural Periods i- = T/.fL7 2

APPENDIX

Table 3 - Experimental Data for Wave Tests on Destroyer Escort Model 8

Table 4 - Experimental Data for Wave Tests on Series 60,

0.60 Block Coefficient 10

Table 5 - Experimental Data for Wave Tests on M/S SAN FRANCISCO Model 11

Figure

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NDTATION

B Beam

Cb Block coefficient

p Froude number

po Still water Froude number

H Draft

h _{Wave height,trough to crest}

L _{Length between perpendiculars}

V Speed

Vd Design speed in still water vo Still water speed

Displacement

À Wave length

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ABSTRACT

This report presents the results of an experimental study to determine the effect of various parameters governing speed reduction in a seaway. Models of three typical ships (block coefficients varying from 0.50 to 0.75) were tested in head seas in regular waves, ranging in length from approximately one-half to twice

ship length, for several wave heights and still water thrusts. fhe speed loss due to the added resistance in waves was determined for each condition. The results are presented in the form of graphs showing the critical wave lEngth (wave length for maximum speed loss) as a function of wave height and still water speed. Also included are plots showing the percentage speed loss for constant wave lengths as a function of the above parameters; and contours of constant speed loss in waves of various lengths and heights. Finally, graphs are presented comparing the performance of the three vessels.

INTRODUCTION

At the present time no criteria are available from which the limiting acceptable sea conditions for conducting speed trials can be determined. Consequently, it has been the general practice to wait for almost perfect weather conditions so that reliable results could be assured. lt was the original purpose of this project to establish the threshold conditions under which a ship's speed is affected by the seaway. These threshold conditions could then serve as a general guide in evaluating full-scale trials. Thus, the study should have been

re-stricted only to mild sea conditions. However, the testing accuracy is relatively poor in these conditions and since the present tendency is to go to higher sustained speeds at sea, the orig-inal purpose of the study was extended to include some generalinformation on factors govern-ing speed reduction in a seaway. Accordgovern-ingly, the tests were carried out under more serious sea conditions than those required for establishing the threshold conditions, the latter then being

obtained by interpolation to the condition of small sea. The results of the present study, while containing information pertinent for evaluating standardization trials, may also provide general information on speed loss at sea.

DESCRIPTION OF TESTS

Models of three typical ships were tested in the 140-ft basin. In this facility a gravity-type dynamometer is used as the towing mechanism and waves are produced by a pneumatic-type generator. Wave heights are measured by a capacitance-pneumatic-type gage where the unbalance of the bridge is a function of the immersion of the element.1 The bridge output is recorded by a Sanborn-type recorder.

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The models tested were a 6.42-ft model of a destroyer escort, a 5-ft model of the Series 60 parent form of 0.60 block coefficient,2 and a 5-ft model of the cargo ship i/S SAN

FRANCISCO. The ship lines are shown in Figures 1 through 3 and the form characteristics are listed in Table 1.

TABLE i

Characteristics of Ship Forms

The lines of the ships selected for the work represent a considerable range in ship form. The destroyer escort has fine lines and a low block coefficient (Cb = 0.50), the SAN FRANCISCO

has full lines with a block coefficient of 0.75, and the Series 60 is between the above two extremes with a block coefficient of 0.60.

The models were ballasted for displacement and draft conditions corresponding to that listed in Table i for the ships. The radius of gyration determined by the bifilar method was 25 percent of the length for each of the models. The dimensionless natural periods associated with these radii of gyration are listed in Table 2.

TABLE 2

Dimensionless Natural Periods

Characteristics Destroyer Escort Series 60 M/S SAN FRANCISCO

Model Number 4369 4509 3572-5A

Length LBP, ft 308 400 429 Beam B, ft 36.7 53.33 59 Full Load Draft Amidships, H, ft 11.5 21.33 24.37 Corresponding Displacement , tons 1802 7807 13,264.4 Block Coefficient, Cb 0.50 0.60 0.75

Design Speed, knots 25 17 14

Sh Natural Pitching Period Natural Heaving Period Destroyer Escort 1.39 1.34 Series 60 1.77 1.77 M/S SAN FRANCISCO 1.93 1.88

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Each model was first tested in still water and the tow force was determined at several speeds. rests were then conducted for three still-water thrusts corresponding approximately to 33, 67, and loo percent design speed in head seas in regular waves whose length ranged

from approximately 0.5 to 1.5 ship lengths. The tests were made at wave heights of 1, 2, and 3 in. model scale corresponding approximately to values of ship length to wave height of 60, 30, and 20. Because of the severity of some of the above specified conditions the speed re-duction was found to be so serious that the forward speed of the models could not be deter-mined with any certainty. These regions of uncertainity are indicated in the graphs by the dotted lines.

The range of test conditions was somewhat limited by the capacity of the facility used. To the extent that this range did not include possible sea conditions, the results are incom-plete.

DISCUSSION OF RESULTS

In order to establish reference conditions for the wave tests, tow forces were found for a series of speeds in still water. These forces were then corrected for the tare in the towing system and the resistances so obtained are plotted in Figures 4a, 4b, and 4e. Wave tests were performed for thrusts corresponding to approximately one-third, two-thirds, and design speed for each of the ships. The experimentally obtained speeds for the various test conditions are listed in the Appendix.

Faired curves of speed versus wave height for constant wave lengths are plotted in Figures 5, 6, and 7. The dashed portions of the curves indicate regions where the data have either been extrapolated since the test conditions were beyond the limit of the test facility used or the speed was somewhat uncertain because of the models' unsteady motion in the more severe conditions.

Figures 8, 9, and 10 obtained from Figures 6 through 7 show speed loss in waves for constant wave heights. From these figures it can be seen that the region for maximum loss in speed shifts toward the shorter wave lengths with increasing wave height for a constant tow force. Furthermore, as the tow force is increased, the critical region shifts toward the longer wave lengths for any wave height. This can be seen more clearly in Figures 11, 12, and 13 where the critical wave length has been plotted as a function of still water speed for various wave heights. A comparison of these three figures shows that for the same still water Froude number, the destroyer escort experiences maximum speed loss at lower values of À/L than the other vessels. For example, considering the case of a tow force which could produce a speed in still water corresponding to a Froude number of 0.2, the X/L for maximum speed reduction for the destroyer escort was 0.9 while that for the Series 60 and SAN FRANCISCO was 1.0 and 1.13, respectively, when running in waves of h/L = 0.017. The destroyer escort (Figure 11) does not experience maximum speed reduction in waves of X/L of 1.0 and larger, and minimum h/L of 0.017 until a still water Froude number of approximately 0.3 is obtained.

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From the speed reduction curves (Figures 8, 9, and 10) the percentage speed losses were evaluated and are shown in Figures 14 through 20. 1ere the percentage speed loss is shown as a function of wave height (ship scale) for various wave lengths. Figures U through 16 compare the three types of ships where the thrust used for each would produce design speed in calm water, Figures 17 through 19 show the same comparison for a thrust corresponding to approximately two-thirds design speed and finally, Figure 20 shows the percentage speed loss for the destroyer escort with thrust for one-third design speed in still water, rests were not

made at this thrust for the Series 60 and the SAN FRANCISCO, rhe speed in waves of these models at this thrust was so low that the accuracy and reliability of the results obtained in the

facility used were in question. The difficulty of measuring low speeds arises from the fact that the motion of the model produces waves which disturb the prescribed wave pattern which

in turn results in unsteady model motion.

A more useful presentation of the information contained in these figures is given in Figures 21 through 26. These figures show the combination of wave heights and wavelengths which result in 1, 5, 10, and 20 percent speed loss for each ship. Figures 21 and 22 are appro-priate for the destroyer escort with thrust for design and two-thirds design still water speed. Figures 23 and 24 pertain to the Series 60 and Figures 25 and 26 to the SAN FRANCISCO for

the above thrust conditions. Figures 21 through 26 may prove useful when determining the limiting sea condition in which standardization trials may be conducted. The acceptability of the sea condition depends on the type of ship and applied thrust as well as on the wave dimensions. If a maximum speed loss of 1 percent is permissible, Figure 21 shows that stand-ardization trials for the destroyer escort (with thrust for design speed in still water) can be conducted effectively in waves whose length is 75 percent of the ship length if the wave height

is no greater than 3 ft. In longer waves the trial results will still be usefulif the wave heights are smaller; at the critical wave length (X = 1.141), the maximum acceptable wave height is 2 ft. At the lower thrust (Figure 22) the 1-percent speed loss is obtained for X/L =

0.75 when the wave height is approximately 1 ft. Figures 23 and 25 show that acceptable sea conditions for trial purposes at design speed are more limited for the cargo and merchant ships. For the ships which these represent, trials should not be run in waves higher than approxi-mately 2.5 ft if the wave length is as large as 0.75L, and at the critical wave lengths the wave height should not be greater than 0.5 ft. A comparison of Figures 23 and 24, and 25 and 26,

show the more limited extent of acceptable sea conditions for conducting the trials when the thrust is reduced.

Figures 27 through 31 compare the performance of the three ships in waves of constant height. Figures 27 and 28 show the speed reduction for thrust for design and two-thirds design speed in still water, respectively, in waves of h/L = 0.017. Figures 29 and 30 show the same comparison in waves of h/L = 0.033. The dashed line represents the estimated speed for the SAN FRANCISCO obtained by extrapolation from the original data. Figure 31 compares the speed reduction for the three models in waves of h/L 0.017 for a thrust which would

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nondimensionalized by dividing by the still water speed V0; namely, design and two-thirds design speed for the respective ships. Consequently, these figures do not compare the re-lative performances at identical values of the still water Froude number F,. Therefore, proper interpretation of these figures requires that one consider not only that the ships represent different degrees of fullness, but also that the still water speeds for the three ships differ. In each of these figures it is seen that the critical region for speed loss in waves of constant height occurs at approximately the same X/L value for the three models. For example, in

Figure 27 for h/L = 0.017 and V0 = Vd, the design speed in still water, the maximum speed loss occurs around X/L = 1.15. For the higher wave height h/L = 0.033 and the lower thrust V0 = 2/3 Vd, the critical region, while the same for the three models, shifts toward the shorter wave lengths. These figures show also that the destroyer escort loses considerably less speed

than either the cargo or merchant ship, there being little difference between the latter two with the exception of the case of h/L. = 0.033 and thrust for two-thirds design speed. While the variation in block coefficient is greater between the Series 60 and the SAN FRANCISCOthan

between the destroyer escort and Series 60, it must be remembered that the design speeds of the Series 60 and the SAN FRANCISCO are much lower (17 and 14 knots, respectively) than that of the destroyer escort (25 knots). It is well-known that slow ships lose more speed in a seaway than a fast ship, under identical conditions.

In Figure 31 a comparison of the speed loss for the three models is made for waves of h/L = 0.017 and V0 = 14 knots (ship scale). When compared at the same still water speed, the Series 60 and SAN FRANCISCO showed the same maximum speedloss while the destroyer

escort's loss in speed was 7 percent less. It can also be seen in the figure that the critical

wave length to ship length ratio shiftstoward the higher values for the models of fuller form.

CONCLUSIONS

This study shows that if a 1 percent error is acceptable, standardization trials can be effectively conducted for the destroyer escort with thrust for design speed (25 knots) in waves whose length is as large as 0.75 ship length if the wave height does not exceed 3 ft. At lower thrusts the acceptable sea conditions are correspondingly reduced. The acceptable sea condi-tions for standardization trials on slower and fuller ships of the Series 60 and SAN FRANCISCO

type are more limited.

A comparison of the speed loss experienced by the three models with thrust for the same still water speed shows equivalent speed loss for the merchant and cargo ships with the speed loss for the destroyer escort being less by 7 percent.

The critical wave length (wave length for maximum speed loss) for constant thrust was found to shift toward the shorter wave lengths with increasing wave height. For any wave height, the critical region shifted to the longer wave lengths as the tow force was increased. This trend was observed for each of the models tested.

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APPENDIX

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TABLE 3

Experimental Data for Wave Tests on Destroyer Escort Model

Thrust for design speed = 6.06 fps).

Thrust for 67 percent design speed (V =4.00 fps).

Wave Length A ft Wave Heighth in. Speed V fps Wave Length A ft Wave Heighth in. Speed V fps Wave Length A ft Wave Heighth in Speed V fps 3 4 0.84 0.94 1.02 1.37 1.51 1.57 1.58 1.82 1.89 2.24 1.01 1.45 1.98 1.98 2.12 2.75 2.85 6.02 6.02 5.99 5.94 5.94 5.90 5.92 5.88 5.87 5.88 5.98 5.95 5.96 5.90 5.87 5.86 5.84 5 6 7 1.03 0.93 1.11 2.03 2.44 2.67 2.69 3.18 1.00 2.01 2.96 3.05 0.99 1.84 2.10 2.81 3.01 3.03 3.09 5.93 6.04 5.92 5.82 5.80 5.73 5.71 5.64 5.98 5.63 4.98 4.88 5.88 5.42 5.20 4.21 3.95 3.97 3.91 7.5 8 3.10 3.11 0.96 1.87 1.92 3.06 1.00 2.03 3.08 3.14 4.17 4.02 5.90 5.48 5.38 4.41 5.90 5.53 4.98 4.93 Wave Length A ft Wave Heighth in. Speed V fps Wave Length A ft Wave Heighth in. Speed V fps 3 0.77 3.92 6 1.11 3.53 0.88 3.91 1.96 2.72 1.18 3.84 3.00 1.85 1.63 3.74 3.04 1.83 1.74 3.73 1.79 3.68 1.00 3.61 2.02 3.70 1.08 3.56 2.12 3.68 2.11 2.79 3.10 1.99 4 1.04 3.89 1.92 3.63 8 0.90 3.75 2.06 3.56 2.02 3.18 2.75 3.36 3.09 2.39 2.89 3.33 9 1.01 3.82 5 1.02 3.73 2.04 3.41 1.98 2.91 3.14 2.80 2.71 2.02 2.81 1.92 3.01 1.78 3.09 1.86 ¡

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Thrust for 33 percent design speed (V0 = 2.26 fps). Wave Length X ft Wave Height h in. Speed V fps Wave Length X Wave Height h in. Speed V fps 3 0.87 2.11 7 0.99 1.90 0.92 2.10 2.14 1.38 1.27 1.96 2.24 1.36 1.31 1.99 1.41 1.84 8 1.16 1.94 1.58 1.84 2.00 1.52 2.06 1.61 4 0.90 2.04 1.45 1.78 9 1.16 2.01 1.87 1.40 2.08 1.35 2.08 1.43 5 1.08 1.78 1.97 1.21 2.01 1.19 6 1.14 1.78 1.05 1.77 1.06 1.81 1.93 1.20 2.02 1.21

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TABLE 4

Experimental Data for Wave Tests on Series 60, 0.60 Block Coefficient Thrust for design speed = 3.32 fps).

Thrust for 67 percent design speed (V0 = 2.23 fps).

Wave Length . ft Wave Height Speed ' fps j Wave Length A ft Wave Height h Speed V fps 2 0.44 3.29 6 1.04 2.66 0.98 3.24 1.97 1.85 2.88 1.19 3 0.59 3.27 _2.96 _1.22 1.05 3.23 _3.04 _1.17 1.85 2.99 I _3.22 _1.16 2.45 2.88 7 0.97 2.99 4 0.61 3.26 _1.96 _2.43 1.02 3.15 _3.06 1.83 2.04 2.04 2.09 2.13 8 0.86 3.20 2.17 2.21 1.91 2.84 2.20 2.08 2.85 2.39 5 1.04 2.69 9 1.04 3.24 2.01 1.43 2.09 3.05 2.11 1.38 3.04 2.72 2.13 1.43 Wave Length A ft Wave Height h in. Speed [ fps Wave Length A ft Wave Height h in. Speed V fps 2 3 4 5 6 7 0.37 0.44 0.95 0.59 1.16 1.87 1.00 1.89 2.01 1.04 2.00 2.08 1.00 2.05 2.09 1.01 1.91 2.19 2.20 2.15 2.14 2.04 1.65 1.67 0.76 0.78 1.50 0.81 0.83 1.76 1.19 1.20 1.96 1.48 8 9 0.89 1.97 1.08 2.14 2.11 1.78 2.11 1.93

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TABLE 5

Experimental Data for Wave Tests on NI/S SAN FRANCISCO Model Thrt for design speed (V0 = 2.56 fps).

Thnt for 67 percent design speed (V0= 1.72 fps).

Wave Length A ft Wave Heighth in. Speed V tps Wave Length A ft Wave Heighth in. Speed V Ips - Wave Length x ft Wave Heighth in. Speed V Ips 2 3 4 0.52 0.56 0.59 0.60 1.08 1.54 1.60 0.50 0.61 0.99 LOO 1.40 1.61 1.62 2.52 2.52 2.53 2.52 2.41 2.22 2.26 2.48 2.42 2.32 2.33 1.97 1.87 1.82 5 6 0.92 LOO 1.98 1.98 2.00 0.93 0.95 2.03 2.04 2.05 1.00 1.03 1.93 1.93 1.98 3.04 2.06 2.05 1.17 1.15 1.18 2.00 1.99 1.23 1.23 1.21 2.27 2.27 1.81 1.81 1.79 1.46 7 8 3.10 3.16 0.86 0.88 1.84 1.84 2.92 U.97 0.98 2.02 2.04 3.12 3.17 1.37 1.43 2.41 2.44 2.11 213 172 2.48 2.50 2.24 2.27 1.95 2.02 Wave Length A ft Wave Heighth in. Speed V fps Wave Length A ft Wave Heighth in. Speed V Ips 2 0.44 1.65 6 0.99 1.21 0.49 1.62 1.03 1.21 3 0.60 1.60 1.03 1.23 0.60 1.60 7 0.94 1.49 1.13 1.34 1.00 1.48 1.13 1.34 1.90 1.00 4 0.62 1.46 8 0.81 1.58 1.06 1.11 0.92 1.60 1.13 1.06 1.74 1.24 1.46 0.74 9 1.11 1.44 5 0.87 1.19 1.11 1.47 1.01 1.19 1.03 1.17 1.04 1.20

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1.4 1.2 1.0 C o C : 0.6 o (I) 0.8 04 02 o o l.0 2.0 30 40 Model Speed in ft./ssc.

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Figure 4c - U/S SAN FRANCISCO

Figure 4 - Still Water Resistance of the Three Models

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Figure 6 - Speed versus Wave Height for Constant Wave Length, Series _60, 0.60 Block Coefficient Ai =0.467 A/ L = 0.624 A/ L=0.780 A/L=0.935 A/L= .25 A/ L .40 A/L= .09 _______ A/L =0.467 AIL 0.624 A/L= .40 A/L=0935 A/L= .25 _______ A/L =0.78 A/L=l.09 A/L 1.40 AI L 1.25 A/L=0.62 _A/t=0.935 L=l.09 X/L=O.467-' _A/L0.780 - AIL0.6 AILl.8 AIL=I.4 - A/L=I.0 A/LO.6 .

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Figure 5 - Speed versus Wave Height for Constant Wave Length, Destroyer Escort

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Wove Height (Model), h ¡n inches

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Wove Height to Ship Length Rollo

M/S SAN FRANCISCO

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Wove Length (Model), A in feet

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0 48 96 144 196 240 288 336 384

Wove Length (Ship), Am feet

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0 0.25 0.50 075 1.00 1.25

Wave Length to Ship Length Ratio

Figure 8 - Speed Reduction Curves for Destroyer Escort

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Wave Length (Model), À in feet

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0 80 60 240 320 400 480 560 640

Wove Length(Shp), Am feet

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0 0.25 0.50 0.75 1.00 1.25 1.50

Wove Length to Ship Length Ratio

Figure 9 - Speed Reduction Curves for Series 60, 0.60 Block Coefficient

O I 2 3 4 5 6 8

Wave Length (Model), Am feet

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o ioo 200 300 400 500 600 700

Wove Length (Ship), Am feet

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0 0.25 0.50 0.75 .00 1.25 1.50

Wave Length to Ship Length Rotio

Figure 10 - Speed Reduction Curves for M/S SAN FRANCISCO

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Figure 11 - Critical Wave Length as a Function of Speed and Wave Height, Destroyer Escort

t I t

0 5 IO 15

Ship Speed in knots

360 r e 336 _C 240 Q 312 CI) C o. C e 288 -o a o 264 .! L) h/L00L3 h/L 0.026 h/L -0.039

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Froude Number

Figure 12 - Critical Wave Length as a Function of Speed and Wave Height, Series 60, 0.60 Block Coefficient

05 IO 1.5 20 2.5 3.0 35

Model Speed in ft/sec (Still Water)

o e e 0 C o Q O

r

o. iO t. o a 0 o L) o

(24)

50 25 knots A/L' 1.09 A .4114 A/L'0.780 A, A/L A/L0.467 L '0.312 1.3 6. 5 o o 550 4' r 1.2 -a' C C _{h/L '0017} ₅₀₀ -J a

r

h/L '0.033 a (I, o G 450 a' a' a' w -j 1.0 5.0 C 4' -J

/

C o _o o 400 0.9 4.5

/

o i-,

,

i-) 350 0.8 4.0 o 0.l 0.2 Fraude Number

M/S SAN FRANCISCO

o 05 .0 5 2.0 25 30

Model Speed n f /sec (Still Water)

o 5 IO l5

Ship Speed in knots

o 0.01 0.02 0.03 0.04 0.05

Wave Height to Ship Length Ratio

Figure 14 - Speed Loss in Percent for Constant Wave Length with Thrust _for Design Speed in Still Water, Destroyer Escort

4 8 2 IS

Wave Height in feet

40 o -J 30 a Cd, 20 a-IO

(25)

50 (I) w a. o a-50 40 o -J w w 30 e 20 Io I X/LI.2 A/L0.8 A/LI.Ø A/L=I.4 A /L0.6 A/L 1.6 A/L1.8 I0 IS

Wov,J Height in feet

I I I I i

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Wove Height to Ship LenQth Ratio

Figure 16 - Speed Loss in Percent for Constant Wave Length with Thrust for

Design Speed in Still Water, M/S SAN FRANCISCO

20 25 30 V0I7.5knots

_____r

A/L0.8

_vMa

AIL 0.4 o 5 IO 15 20 25 30

Wove Height in feet

I i I i

0 0.01 o.oa 003 0.04 005 006 0.07

Wove Height Io Ship Length Ratio

Figure 15 - Speed Loss in Percent for Constant Wave Length with Thrustfor Design Speed in Still Water, Series 60, 0.60 Block Coefficient 40 e -J 130 a. o 20 (J a-lo

(26)

o -j 50 40 0 w w 30 Q, w o o c 20 w o-Io 50 V0 16.4 knots

4

_?íLl.09 A,L=O750 A, L =0.935 A/LI.25 ______

-AIL = 0624 =0.467 AIL A/L =0.312 A/L A/L=0.6 A/L=I.2

1.0-A/L=I.4 V0 II.9 knots

/ A L 0.6

AI L = 1.6

AILI.8

o 5 IO 15 ₂₀ ₂₅

Wave Height in feet

I i i I

0 0.01 0.02 0.03 0.04 0.05 0.06 0.07

Figure 18 - Speed Loss in Percent for Constant Wave Length with Thrust for Two-Thirds Design Speed in Still Water, Series 60,

0.60 Block Coefficient

o 001 0.02 0.03 0.04 0.05

Figure 17 - Speed Loss in Percent for Constant Wave Length with Thrust for Two-Thirds Design Speed in Still Water, Destroyer Escort

o 8 2 16

Wove Height in feet

I I 40 o -j

:

(n o. o 20 o-t0

(27)

30 U) 50 50 40 Io X/L08 À/L0.6 V0 9.4 knots À / L 1.0 À! L 1.2

4--V o 9.3 knots À/L .25 À/L0.624 À/L .09 _À/LI.40 À/L0. 467 X/L 0.3I2 5 IO 15 20 25 30

Wove Height in feet

I I I I

0 '0.01 0.02 0.03 0.04 0.05 0.06 0.07

Figure 19 - Speed Loss in Percent for Constant Wave Length with Thrust for Two-Thirds Design Speed in Still Water, M/S SAN FRANCISCO

o 4 8 12 16

Wove Height in feet

0 0.01 0.02 0.03 0.04

Figure 20 - Speed Loss in Percent for Constant Wave Length with Thrust for One-Third Design Speed in Still Water, Destroyer Escort

40 o -j : 30_a U) e 20 4, o-IO

(28)

r

24 2 I2 a,

I

o 4 24 20 4 \ \ \_' \ \ \ \ 20 percent IO percent 5 pe rc \ \ \

\

s

\

.,

\

_\

20 percent IO percent 5 percent N I p e o lOO 200 300 400

Wove Length in feet

Figure 21 - Contours of Constant Speed Loss with Thrust for Design Speed, Destroyer Escort

lOO 200 300 400

Wave Length ¡n feet

Figure 22 - Contours of Constant Speed Loss with Thrust for Two-Thirds Design Speed, Destroyer Escort

6 a, a, C 12 a,

I

(29)

24 20 4 24 20 4

/

/ / / /

-

_{20 percent} IO 4 percent 5 percent I perc e n t / / / 'i 'i

f

/ / 20 PercentA iopercent 5 percent I percent o 200 400 600 800

Wove Length in feet

Figure 23 - Contours of Constant Speed Loss with Thrust for Design Speed, Series 60, 0.60 Block Coefficient

o 200 400 600 800

Wave Length in feet

Figure 24 - Contours of Constant Speed Loss with Thrust for Two-Thirds Design Speed, Series 60,

0.60 Block Coefficient 16 e . 12 z e

(30)

24 20 4 o

A

u JE

_r

.4 _dll4

I percent

u---20 percent

Wove Length in feet

Figure 26 - Contours of Constant Speed Loss with Thrust for

Two-Thirds Design Speed, M/S SAN FRANCISCO

200 400 600 800

Wove Length in feet

Figure 25 - Contours of Constant Speed Loss with Thrust for Design Speed,

M/S SAN FRANCISCO IO percent 5 percent 20 percent IO percent 5 percent I percent 200 400 600 800 24 20 6 w 4) = l2

I

(31)

1.0 0.8 06 > Nil., > 0.4 0.2 Destroyer Escort Series 60 SAN FRANCISCO Destroye Series 6 SAN FR 0 02 04 06 0.8 LO 12 14 16 .8

Figure 28 - Comparison of Speed Reduction of the Three Ships for h/L = 0.017 and Thrust for Two-Thirds Design Speed in Still Water

0 02 04 06 08 IO 2 14 1.6 Is

Figure 27 - Comparison of Speed Reduction of the Three Ships for h/L = 0.017 and Thrust for Design Speed in Still Water

1.0

0.8

0.6

0.4

(32)

0.2 I.0 0.8 0.2 I.0 0.8 0.6 0.4 0e st ro ye Series 6 SAN FR r Escort o ANCISCO

--

P"_

Destroyer Series 60 SA N FRA Escort NC I 0 02 0.4 0.6 02 IO 2 4 16 8

Figure 29 - Comparison of Speed Reduction of the Three Ships for h/L = 0.033

and Thrust for Design Speed in Still Water

0 02 04 0.6 0.8 IO .2 14 6 1.8

Figure 30 - Comparison of Speed Reduction of the Three Ships for h/L _{= 0.033} and Thrust for Two-Thirds Design Speed in Still Water

06

NI

>

(33)

Figure 31 - Comparison of Speed Reduction of the Three Ships for h/L = 0.017 and Thrust for 14 Knots in Still Water

REFERENCES

Campbell, W.S., "An Electronic Wave Height Measuring Apparatus," David Taylor Model Basin Report 859 (Oct 1953).

Todd, F.H., "Some Further Experiments on Single-Screw Merchant Ship Forms

-Series 60," Transactions of the Society of Naval Architects and Marine Engineers (1953).

1.0 08 o c 0.6 >0 04 >0 > 0.2 0

.---.

- - Destroyer Series Escort 60 FRANCISCO SAN

....

02 04 0.6 0.8 lO 12 1.4 16 8

(34)

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