Resistance and seakeeping performance of new high speed destroyer designs

Lab..v.. SCCS!1

Technische Hogescirnol.

R1082

Delit '.

DAVIDSON:.

LABORATORY

REPORT 1082

RESISTANCE AND SEAKEEPING PERFORMANCE OFNEW HIGH SPEED DESTROYER. DESIGNS

by

John P. BreslIn and

King Eñg

RESISTANCE AND SEAKEEPING PERFORMANCE OF NEW HIGH SPEED DESTROYER DESIGNS

by

John P. Breslin and

King Eng

Prepared for the Bureau of Ships

and the

Office of Naval Research Contract Nonr263(l0) (DL Project 2738/060)

R- 1082

TABLE OF CONTENTS

ABSTRACT I I

INTRODUCTION 1

GENERAL CONSIDERATIONS OF RESISTANCE COMPONENTS ₃

GUIDES FOR DESIGN FROM WAVE RESISTANCE THEORY

For Froude Numbers F Less Than 0.30 .. 8

For Froude Numbers in Excess of 0.30 ₉

DESIGN OF tHE MODELS 10

RESISTANCE EXPERIMENTS .

13

MOTIONS IN REGULAR WAVES

CONCLUSIONS . 17

ACKNOWLEDGEMENT 1.

REFERENCES .. ₁₈

ABSTRACT

Results of calm water resistance tests for two new destroyer de-signs are compared with data for the DD692 Class (long hull). Heave and pitch measurements In three wave lengths, which are reported for the better of the two new designs, show Its marked superiority over 692 In all but the very low speed range. A check of the roll characteristics shows that the gain In seakeeping performance is obtained at small sacrif Ice In roll sta-bllity which may be overcome by design refinement. t Is concluded that this brief study has evolved a highly practical destroyer form which has markedly reduced heave and pitch with some Increase in resistance at low speeds and a reduction In resistance at high speed. This form, which merits consIderatIon for additional study, holds greater seakeeping potential for ASW missions than any other advanced surface-ship concept previously studied.

-II-R- 1082

I !'ITRODUCTI ON

The United States Navy through t,he efforts of the Office of Naval

Research and the Bureau of Ships has, overthe past several years, encouraged renewed searches for new hull designs capable of.hlgher sustained speeds In a given seaway with reduced response. As a result, studies have been made of rather bold concepts such as semi-submerged ships1 and hydrofoil-controlled

semi-submarines2. While these unusual forms result in Improvement with re-spect to certain of the sea-induced motions, they appear to be vastly imprac-tical in many respects. It is the purpose of the present study, reported herein, to demonstrate that very important gains in seakeeping can be made within the. framework of. more conventional design practice without sacrifice

of the very practicairequireinents which must be met by any combatant ship.

The original purpose of the investigation reported herein was to develop a new destroyer design which would have reduced wave resistance at maximum speed, about the same resistance at low speed and reduced motions

in rough water as compared to DD692 (long hull) class. The main objective was reduced motions with, hopefully, gains in calm water performance and no appreciable sacrifice in other important ship -characteristics. The design of the new hulls was dictated largely by wave resistance considerations and, hence, a considerable portion.of this reportjs, devoted toa sumnry, in generally non-mathematical terms, of what guides are now available from ship wave resistance theory.

It is well to realize that present design procedure depends much upon the naval architectts experience and intuition. His chief guide to de-sign of good lines from resistance and seakeeping viewpoints has been model basin data on a methodical series of models. The choice of the parent form for such series has been arbitrary with hydrodynamical qualities playing only a part in the selection. The best of. such methodical serIes cannot be justified as the best of all possibilities and, hence, it is morethan prob-able that a better form exists outside of the series examined and, therefore, outside of the experience of the design organization involved.

With these thoughts in mind, it was decided to see what improvement In the hydrodynamic performance of destroyer designs could be achieved by

departing from conventional destroyer lines, but retaining important restraints

-1-such as displacement, length, beam, draft and, hopefully, roll stability. The broad procedure adopted was to utilize the guides provided by modern

ship wave resistance theory with the thought that the resistance at both cruise and maximum speed must be maintained or reduced In any acceptable design. Put another way, It is believed (at Davidson Laboratory) that any design which exhibits better seakeeping qualities at any significant

sacri-fice of powering requirements in calm water would ultimately be rejected by the Navy as impractical. it was hoped that a design which would mitigate against the development of large wave resistance would also provide

con-siderably reduced motions in waves.

This report describes the process involved in the design of two destroyer hulls, relates the tank tests conducted and presents the results

together with the pertinent properties of the hulls to permit a complete and valid comparison with the 692 (long hull) destroyer class. it is

es-sentially a re-orientation of a more detailed report written by Prof. H. Maruo and Mr. King Eng3.

This work was Jointly supported by the Bureau of Ships and the Office of Naval Research under continuation of NR Contract Nonr263(l0), Davidson Laboratory Project 2738/060.

-2-R- 1082

GENERAL CONSIDERATIONS OF RESISTANCE COMPONENTS

The total calm water resistance of a surface vessel is made up of the longitudinal components of the tangential and normal stresses exerted

by. the fluid. The tangential stresses are of the order of those estimated

by the usual turbulent flat plate formulations with an Increment associated with the form of the ship. The work of Hughes4 Indicates that the form

fac-tor on frictional resistance Is largely related to displacement-length ratIo and the beam-draft ratio. Since both of these factors are fixed In the pres-ent Investigation, there Is no gain to be expected from variations of form on skin friction. While It, is always important to avoid excessive wetted surface, It is not likely that variations In wetted surface with changes In form wilibe significant.

.Thus,attentlon Is immediately directed to the normal stresses which are composed of pressures associated with wave-making and viscous form ré-sistance. This latter component is known to depend upon the shape or, more directly, on the pressure distribution at the stern as altered from the In-viscid values because of distortion provided by the thick boundary !ayer.. Viscous form drag is part1cu1arl large when separation occurs as In the case of hulls with very full sterns. As the sterns of high-speed naval craft are generally fine, separation Is not a problem, although the stern flows, about cruiser-type sterns at speed may properly be thought of as com-pletely ventilated, separated flows. The drag coefficient produced by such sterns Is less when ventilated to the full draft (at the stern)than it would be were it fully wetted, as at very low speeds. It seems that the presently conceived stern designs may be retained as they do not contribute much form drag, although there has not been an extensive study of the form drag of ttcrulsertt versus "canoe" type sterns. in any event, It is far more Important to fOcus attention on the wave-making characteristics of the bow.

-3-GUIDES FOR DESIGN FROM WAVE RESISTANCE THEORY

Since the advent of Michell's theory In 1898 for the wave resistance of thin ships, many scientists have endeavored to show how this theory can be used to predict the influence of various form parameters and shapes on the wave resistance of ships. While It Is still true that this theory (which

Is applicable to thin ships In non-viscous fluids) does not predict with suf-ficient accuracy that part of the residuary resistance (from model tests) which has been thought to be the wave resistance, It has been successful In

correctly predicting trends to be expected by changes In form and in Isolat-ing those features of the hull which are dominant In each Froude number range. More recently, the engaging work of Inul In applying large bulbs to ship

models has focused attention on the possibilities of the variations In hull shape for significant wave drag reduction which may yet lie undiscovered. Theory developed by Kotik, et al5 and Maruo6 has confirmed the earlier esti-mates of Pavlenko7 (19311.) that the waterline shapes for low wave resistance of strutlike ships (Infinite draft) are like those drawn by naval architects at low and moderate Froude numbers, but are relatively blunt-ended and "dog bone" shaped for high Froude numbers In the range of 0.11. to 0.50. The pdiction of the precise shapes of the relatively blunt ends for low wave re-sistance at large Froude numbers (corresponding to speed-length ratios of 2.0) is open to question since the restrictions to small slopes in the

devel-opment of the theory Is strained (If not vlolated)by these results. However, Increase In the fullness of the ends at high speed-lengths Is not contrary to design practice as naval architects usually increase the prismatic coef-ficient for elevated speeds as compared to what they would use at moderate speeds.

More careful scrutiny of the mathematical problem of minimizing MichelPs integral with the constraint of constancy of displacement has revealed though the work of Bessho8 that no single answer exists. This may be due to the fact that the problem has been treated In a restricted manner. Physically, it seems plausible that there exists an infinity of forms with the same wave resistance because this Is an integrated effect to which each element of the form can contribute. A form of zero wave resistance has been mathematically developed by Y1m9 by using an Infinitely long vertical dis-tribution of doublets along the stem whose strengths are such as to cancel

R- 1 082

the waves due to the longitudina.l distribution of sources forming the hull. Although Vim's configuration is not practical, the mathematical discovery of a wave-free combihation is highly significant. Even greater flexibility

in the mathematical constrüctiön of ship hulls has been achieved by Vim's introduction of the quadripole into wave drag theory.

Even more recently, work by Maruo'° and others On slender body ap proachés to the representation of ship hulls has provided estimates of sec-tional area distributions for reduced wave resistance. Maruo has presented curves of sectional area distribution for minimum wave resistance from slen-der ship theory as deduced by the limiting forth of Michell's theory when the draft is pressed to zero. Curves of these sectional areas for seven valUes of the Froude number are shown in Figure 1. The practical naval architect may take some comfort from the fact that these "optimUm" sectional area curves Imply an optimum prismatic coefficient variation with Froude number which Is not very far from that which can be secured. from Taylor's .curves

of residuary resistance as may be seen in Figure 2.

it is helpful to think of the wave resistance of a ship in terms of the contributions of each element of the ship surface In generating its. own wave train plus the interactions of these wave trains witheach other.

Elements of the ship may be envisioned to consist of discrete panels of the wetted surface that may be generated hydrodynamically by locally-uniform source distributions.whose strengths are determined to satisfy the requirements of a stream surface which agrees with the form of the ship. This means that the source strengths m. must be determined to take Into account the presence or contribution from all the neighboring sources as well as the presence of the free surface. The contribution of each ship

panel to the wave resistance can then, in principle, be traced because the wave resistance is expressible as a square matrix:

-5-where and Rw Rw -p1J212 *

A proof that the interference terms arise only from the action of forward elements on after elements and not from after elements inducing forces on' those forward will be given in the near future.

-6-2 r1. rj. = J cos(F..sece) cos(fljsec28sinê)e_C1J5ec esec3ede

= k0(x;x)

iJ = k0(v1-.) ; = k0(z1-z) (2)

In which the x,y,z are the coordinates of the center of the source panels

and _ko is the wave number g/U2 and the dummy variable' 0 is the angle between the normal to the wavelet crest and the direction of ship motion. The wave resistance of a ship can be seen from Equation (1) to consist of

the wave resistance of the sources themselves as provided by the main di-agonal terms which are proportional to the squares of the source strengths. The off-diagonal terms which are proportional to the

products mm(I

represent the interference resistance caused by the constructive and destruc-tive coupling of the waves produced by the forward sources with those

pro-*

duced by the after sources. The influence of the after sources on the for-ward sources is felt through their contribution to the source strength in

satisfying the boundary condition on the hull. This Interplay is completely absent in the thin-ship theory because the hull boundary conditions are ap-plied'on the longitudinal centerplane over which sources are distributed. The velocities induced normal to a planar distribution of sources are made up by the contributiOn of only the source 'element at each point; all other sources' are 'Unable to "look in" or cont'ribute because of the flatness of -the surface. Thus, in thin ship theory the source strengths are found to be

dependent only upon the local' fore-and-aft slopes of the static waterlines, whereas in surface distributions the source strength depends not only on the

local directio'n of the' normal, but also upon the curvature and' higher order

(m,n

2 R

1082

derivatives of the hull in the locality of the source. From this repre-sentation, it Is at least plausible that considerable variation in wave

resistance might be expected from the myriads of shape variations that are possible to use in constructing ship lines..

It is most important to realize that this method of calculating the wave résistance holds out the distinct promise of isolating the direct contribution of each element of the ship to the theoretical wave resistance. This might be done by instructing the computer to print out th,e contribution of each main diagonal term in the matrix. The interference or off-diagonal terms can lso be sumed to find the net interaction of each panel with all the other panels. In this way, a plot showing the "resistance density" of each section may be displayed and, for each section, the vertical distribu-tion of contrbutioris can be made to display the role played by sources near the surface as well as those throughout the draft. This analysis was looked into during the calculation recently made by Breslin and Eng" but the Jim-. ited budget available for this work precluded the rather extensive computer program modification to effect this breakdown of relative contributions to the total theoretical wavemaking resistance.

A further decompositiøn of the contributions of each ship panel to the wave resistance can be made by isolating that part attributable to trans-verse waves and that to lateral or divergent waves. This can be done by breaking the integral over the dumy wave direction angle 0 in Equation (2) into two parts, viz., from e = 0 to =

_0.633

radians

(35°l6')

and

from =

0.633

radians to ,r/2. The resistance connected with transverse

waves is given by the integral over the range 0 to 35016, and that con-nected with lateral waves is associated with the range 35016? to 90 degrees.

Such a breakdown has been carried out by Lunde12 for the case of a thin ship having parabolic waterlines and parabolic sections. The curve from Lunde's paper is reproduced here in Figure 3. Here it may be observed that the relative contribution of transverse and lateral waves varies quite strongly with Froude number. For example, at F =

0.30

transverse waves account for 75 percent of the total wave resistance,whereas at F =

_0.35

transverse waves account for only 17 percent of the total. At the maximum valtie-of wave drag coefficient which occurs at F -= 0.50, the transverse

-7-and lateral waves each contribute half of the total. Thus, the thin ship theory, to the extent that it can be relied upon, (see discussion which follows) Indicates that efforts to reduce wave resistance by developing form perturbations which develop principally transverse waves may or may not be effective, depending upon the relative importance of these waves at the Froude number of interest.

It is important to realize that all the existing theoretical tech-niques have the two outstanding defects:

the source strengths representing the hull do not include the presence of the free surface at any practical Froude number, and no entirely rational account of the influence of viscosity in

reduction of the pressures at the stern has been made.

It is believed that neglect of these two effects is primarily re-sponsible for the lack of engineering accuracy In the application of theory

to practical hulls, and that this is particularly true in the Froude number range in which the theory shows overly strong "hump" and "hollows" In the resistance curve. It Is clear from observations of the stern waves made by models and their drag data that the stern regions do not provide the wave amplitudes ascribed to them by the inviscid flow theory. Hence the wave

In-terference effects provided by bow and stern sources, as well as the wave drag of the stern sources, are mitigated by the action of viscosity. it would, therefore, appear advisable to concentrate on hull form variations

in the region of the bow, at least for the present. With these various In-dications from theory and experience from model testing, it is possible to

formulate some broad guiding principles:

a) For Froude Numbers F less Than 0.0

In this range, the transverse wave lengths generated by each ship element (or singularity) are sufficiently short as compared to ship length, draft, and beam so that waves produced by forward elements can react or In-terfere with waves produced by after elements. Thus the vertical shape of the sections is important and the wave resistance is particularly sensitive to the water line and buttock entrance angles at the bow. One should expect that an optimum form at a fixed Froude number will exhibit rapidly changing shape in the forward and after quarters as shown in Figure 1. (It is because

-8-wave interference effects are possible. n this Froude number range that the

Inul-type bulb can be effective in reducing wave resistance. Further work. by Inul and Pien has shown that equally remarkable'reductions are possible through hull-shape changes without a bulb).

b) For Froude Numbers In Excess of

_0.30

The relation between the length of a free wave element In terms of an arbitrary ship length and the length-Froude number Is.

x

L 2,-F2cos28

where e is the wave direction angle measured between the axis of transla-tion and the forward-pointing normal to the wave-element crest line. From

(3), it Is readily seen that the length of wavelets associated with trans-verse waves become quite long for F > 0.3, as, for example,

1.57 for and

F= 0.5.

It would therefore appear impractical to attempt to provide for 'wave cancel-lation of transverse wave elements for Froude numbers in this range.. For

lateral wave elements,'thé picture is possibly more attractive because of the strong directionality. For example, an element at e = ./3' (60 degrees)

for F = 0.50 yields ,

x

.

which Is relatively short. It would, therefore, appear possible to design interfering effects into the bow to annul lateral waves. The feasibility. of doing this does not appear to have, been examined in detail from this point of view. The predictions of both ship theories as applied to strut-like ships and slender body theory (vanishingly small draft-length ratio) are that the ends of the form become progressively fuller or that the pris-matic coefficient Increases for hulls of reduced wave-resistance as the Froude number is elevated.

1082

DESIGN OF THE MODELS

The body plan for the DD692 class destroyer (long hull) which was selected as the control design for purposes of comparison is shown in

Fig-ure ii.. The beam, length, draft and displacement were maintained constant and two new designs were evolved by Professor Maruo. In the first of these,

referred to as Design A, the afterbody was kept fairly much the same as the DD692 and the forebody changed in accordance with the guides provided by

both thin-ship and slender-ship theory.

I had been decided to attempt to reduce the resistance of the

des-troyer at the maximum Froude number of Q.14. while maintaining the resistance at a cruising F = 0.29 (19 knots). To do this, Prof. Maruo selected a

sec-tional area curve which may be near to optimum for F = 0.11.0 and then dis-tributed this area vertically to secure near-optimum water plane angles as required for efficient design at low Froude numbers. The body plan thus evolved and shown in Figure 5 is referred to as Design A.

After initial experiments with a model of Design A which showed an undesirable shoulder wave, Design B was evolved by Prof. Maruo with a more accentuated bulbous form faired into the more conventional frame lines closer to the bow and with concurrent changes to "softer" stern lines. The body plan for this hull. is displayed In Figure. 6.

An additional and most important requirement in evolving these de-signs was the reduction of motions in a seaway to improve the effectiveness of destroyers in ASW missions in rough waters. Since the response of a ship at resonance depends heavily on the damping characteristics, it was expected that the strongly bulged forepart would strongly increase the damping and the reduced water plane would also reduce the excitation and change the natural frequencies in heave and pitch somewhat. As will be seen from the observations of the motions in various waves over the speed range, these expectations were far exceeded.

Characteristic dimensions of the three models are provided in Table

I. It is to be noted that the new designs were drawn to provide an increase in prismatic coefficient from 0.6113 (692 class) to 0.693 to provide less re-sistance at high Froude number, a well known practice as indicated in Figure 2.

-10-R- 1082

The midship section was made elliptical to reduce wetted surface, providing

a midship area coefficient of ,.!/14. =

0.785.

The prismatic coefficient of the

forebody of Design A was selected at 0.725, and the curve of sectional area follows the optimum form computed by Maruo from slender body theory at a Froude number of O.!i.0 as shown in Figure 1. in order to avoid excessive resistance at lowFroude numbers, the shape.of the loadwaterline was taken to conform approxImatey to the optimum waterline of an infinite strut at

F = 0.29.

The afterbódy shape was configured to follow thátof the 692 class, butmodf led to secure the total prismatic coefficient of

0.693.

in Design B, a more favorable Interference effect was sought between the sharp-ended main hull and thebulbous lower body. The prismatic and midship coefficients were maintained as in Design A, but the station shapes

in the bow and stern regions were changed significantly. This resulted 1n agreater concentration of displacement in the bow, yielding a more strongly bulbous shape with a resulting finning of the waterlines aft to keep the. dis-placement constant. The forebody prismatic coefficient was increased to

0.733

with .a slight change in shape of sectional area curve. The body plan for B is given in Figure 6.

-Il-Characteristics Model of Long Hull 692 Class Destroyer

Length on LWL, feet

_5.710

_5.710

Wetted surface area,

li.05

sq. feet

Beam, inches

7.25

7.25

Draft, Inches

2.50

2.50

Displacement, pounds -" _o

25.3

25.2

Prismatic coefficient O.61i.3

0.693

Waterplane area coefficient

_0.754

_0.738

Midship area coefficient 0.831

0.785

Block coefficient _0.53)4

_0.579

Gyradius L/li.

Natural pitching period,

0.60

0.71

seconds

TABLE 1

Characteristics of models: Model of 0D692 Class destroyer built to a linear ratio of

_67.c9

-12-Model No. A Model No. B

5.710

3.93

7.25

2.50

25.3

0.693

Natural heaving period,

R- 1082

RESISTANCE. EXPERIMENTS

Models of the DD692 Class (long hull) destroyer and Professor Maruo's Designs A arid B were towed for calm water. resistance. in Tank No. 3 at Davidson Laboratory. Total resistance, as well as sinkage and trim, were recorded over a Froude number range extending from 0.18 to 0.6T. A plot of the total resistance coefficient RT4 pSIJ2 Is provided in F.!gure.7. A comparison of the residuary resistance coefficients defined by Rr/ p12U2

is provided by the plot: in Figure 8 where It may be seen that A shows to ad-vantage at Froude numbers between 0.45 and 0.60 and that the model of DD692 provided 1wer resistance at Froude numbers between 0.20 and

0.40.

Design

B Is generally superior to A in the low speed range and Is the most

resis-tive of all for F > 0.50. It may be concluded that Prof. Maruo's efforts to reduce the resistance at high speed succeeded, Deslgn.A being about 4 percent less resistful at F

= o.4,

but failed to match the low resistance of DD692 at low Froude numbers because of strong interference, effects. The

Increase in total resistance at F = 0.20 is about 5 percent. This

disadvan-tage must be weighed against the remarkable redUction in rough Iater motions which are next considered.

The curves in Figi.ire9 of sinkage reveal, as expected, that A and B are sucked down because of the stronger longitudinal curvature of the bow

lines as compared with DD692. The curves of trim are more favorable, Design

B showing larger trim than A because of the softening of the flat lines aft.

-13-MOTIONS IN REGULAR WAVES

Measurements were made of the heave and pitch of the model of Design A towed in regular waves of lengths 0.75, 1.0 and 1.25 times the model length over a range of Froude numbers from 0 to 0.60. The wave height (double amplitude) used in these tests was 1/11.0 model length, corresponding approximately to the average significant wave height of a State 5 sea. Only

Design A was selected for these tests sInce B has been found to have greater resistance at high speeds and, In addition, did not have as favorable stern

lines as DD692.

Comparison of the pitch and heave motions (In appropriate non-dimensional form) of Design A with those previously obtained at Davidson Laboratory with a model of DD692 (long hull) class are given in Figures

10(a) through 10(f). For a wave length-ship length ratio X/L = 0.75, it is seen that both pitch and heave of Design A are less than the existing destroyer. At /L = 1.0, the pitch response of A is somewhat greater than 692 below F = 0.15, but is remarkably lower for all higher F, being about half as large in the operating range. The response In heave at low F is also unfavorable, but is significantly less in the important speed range. For x/i = 1.25, the advantage of Design A In both pitch and heave is truly

remarkable in the speed range of general interest.

It is conjectured that the generally superior performance of Design A at higher speeds is due to the strong dynamic damping effect produced by the bulbous lower forebody and the smaller excitation arising from the finer

load water plane in the forward region. It is of interest to compare the period of encounter for peak pitch response in these three wave lengths with the zero speed periods obtained by exciting the model in calm water. These values are listed in Table 2.

*

Data questionable

The undamped natural period for either pure pitching or pure heaving at zero speed usually can be well estimated by the following formula adopted from References 13 and 14:

where

T3,T5 are the natural periods in heave and pitch (undamped) in seconds

V is the displacement in pounds g acceleration of gravity ft/sec2

is the weight density of water C is the waterplane area coefficient

C, is the vertical prismatic coefficient

H is the draft in feet, i is the mean draft.

Values of 13 computed from Equation 1, using required values from Table 1, are given in Table 2. It is seen that the computed period for 692 agrees very well with that from both calm water measurements and those derived from the speeds and wave lengths at which peak pitch responses were obtained. The value of 0.62 for Design A is, however, significantly lower than those derived from observations at both zero wave length and at all other wave lengths and, in addition, the periods for A increase with increasing Froude number.

R- 1082

TABLE 2

Comparison of Measured and Computed Noctel Natural Pitching Periods In Calm Water and. Encounter Periods for Maximum Pitch Response

-in.Three Wave Lengths

X/L DD692 (long hull) Design A

-15-1.57V/VH = 1.57/ 0 0.75 1.0 1.25 F 0 0. 15 0.28 0.37 From Measurements o.6o o.64 0.60 0.63 From Theory 0.60 F 0 o.c90 0.14 0.21 From Measurements 0.71 o. 0.79 0.80 From Theory 0.62

The significantly longer period of Design A at zero speed in calm water cannot be accounted for on the basis of the above elementary formula which is derived on the assumption that the added mass Is equal to the

dis-placed mass and that damping has a negligible effect on the natural frequency. It is to be expected that the added mass and damping of Design A are signif-icantly larger than for 692, but since the period depends on the square root of the mass plus the added mass and a quadratic increment depending on the damping, it is difficult to conceive that these quantities could be enough

larger to account for a 15 percent increase In period. Since the added mass is of the order of the ship mass, this would require something of the order of a 60 percent larger added mass for Design A. This feature of Design A, as well as its change in resonant period with speed, are worthy of additional

study.

It may be thought that the better seakeeping performance of Design A Is obtained at a sacrifice of waterplane area and hence of static roll stability. Calculations of metacentric height were made on the assumption of equal center of gravity heights. The results, which are given in Table 3, show that Design A has a GM of

_87.5

percent of that of DD692 (long hull) which would seem to be an acceptable sacrifice in roll stability, at least for preliminary design purposes.

TABLE 3

Comparison of Static Roll Stability Parameters (Ship Scale)

Transverse gyradius k, ft. 16.9 16.9

T (rolling period for i1i ft.

10.0 draft), sec.

-16-G, ft. KB, ft. KM, ft. GM, ft. LCB, ft. from Sta. 10 DD 692 (long hull) 15.7

8.li.

19.2

3.5

8.8

aft Design A 15.7

8.20

18.76

3.06

7.0

fwd.

R- 1082

CONCLUSIONS

The outstanding conclusion which can be reached on the basis of the study reported upon here is that, by a radical change in the forebody section shapes, it is possible to design a very practical destroyer (or Other type of ship) form which has markedly redUced motions in a seaway,

favorable resistance at maximum speed, and tolerable sacrifices in low-speed resistance and in roll stability. This stands in strong contrast- to pre-vious efforts to evolve ships of improved seakeeping--all of which have come through with configurations having highly impractical features.

It is most probable that the deficiencies of Design A can be eliminated or mitigated by further réfihements. The unusually low pitch and heave response of Design A emphasizes the fact that relatively little

is known about the influence of section shape on added mass and damping. It would be most interesting to apply the existing ship-motions computer programs to this form to determine if the experimental results can be well -correlated with theory.

The flatness of the forepart region of Design A does suggest that a problem may exist in regard to slamming. It is recommended that this form be studied further in an effort to achieve abetter powering compromise and

to determine the sea conditions and speed. at which slaming may occur. If the U.S. Navy has need for higher sustained rough water speeds with reduced motions for ASW missions, then serious attention should be given to the

re-suits presented here.

ACKNOWLEDGEMENT

Credit for the effectiveness of this study is due in large part to the.skillful and rapid work of Hajime Maruo, Professor of Naval Architecture, University of Yokohama, Japan, during his brief stay as Visiting Scientist at Davidson Laboratory, May to September 1963.

-17-REFERENCES

Lewis, E.V. and Odenbrett, C.: "Preliminary Evaluation of a Semi-Submerged Ship In High Speed Operation in Rough Seas," SNAME Journal of Ship Research, Vol.

3,

No. 14, March 1960

Uram, E.M. and Numata: "Behavior of Unusual Ship Forms," DL Note 722, July 19614

3..

Maruo, H. and Eng, K.: "A Study of Ship Forms at High Froude Numbers," Preliminary DL Report 986, October 1963

Hughes, G.: "Frictional and Form Resistance in Turbulent Flow, and a Proposed Formulation for Use in Model and Ship Correlation," Trans. of the Inst. of Naval Architects, 19514

Kotik, J., Carp, S. and Luyre, J. "On the Problem of Minimum Wave Resistance for Struts and Strutlike Dipole Distributions," Third Symposium on Naval Hydromechanics, 1960

Maruo, H.: "Experiments on Theoretical Ship Forms of Least Wave Resistance," International Seminar on Theoretical Wave Resistance,

Vol.

3, 1963

Pavlenko, G.: Trudy WNITOSS (Leningrad) 19314

Besho, M.: "On the Minimum Wave Resistance of Ships with Infinite Draft," InternaHonal Seminar on Theoretical Wave Resistance, Vol.

3,

1963

Vim, B.: "On Ships with Zero and Small Wave Resistance," International

Seminar on Theoretical Wave Resistance, Vol.

3, 1963

Maruo, H.: "Experiments onTheoretical Ship Forms of Least Wave Resistance," International Seminar on Theoretical Wave Resistance, Vol. 3, 1963

Breslin, J.P. and Eng, K.: "Calculation of the Wave Resistance of a Ship Represented by Sources Distributed Over the Hull Surface," Inter-national Seminar on Theoretical Wave Resistance, Vol. 3, 1963

Lunde, J.K.: "On the Linearized Theory of Wave Resistance for Displace-ment Ships in Steady and Accelerated Motion," SHAME, N.Y., 1951

Blagoveshchensky, S.N.: "Theory of Ship Motions," Dover Publications, 1962 (Translation)

114. Savitsky, 0.: "Engineering Approximation to Natural Heave and Pitch Periods of Displacement Ships," DL Note 697, May 1963

-18-> 2.0

S...

4

('J 4 'U 4 -J

4

z

0

C) 'U U) 1.0 U) Ui -j

z 0

U)

z

'U 0 FROuOE NO. =

0250

0.266 0.28 9 0.320 0.35 4 0.398 0.500 0.2 0.4 0.6 0.8 tO

xii

FIGURE 1.

CURVES OF OPTIMUM SECTtONAL AREA FOR A SLENDER SHIP

0.75 0.50 0.25 0 REF-tO (MARUO

TAYLOR'S STANDARD SERIES

(DERIVED FROM

OF SHIPS FOR A/(L/tOO)3

TAYLOR-SPEED AND POWER

50

0.2 0.3 0.4 0.5

FROUDE NUMBER-V/-It

FIGURE 2.

VARIATION OF OPTIMUM PRISMATIC COEFFICIENT WITH

14 1.2 0.4 0.2 0 1,082

EQUATION OF MODEL 77:(I_C2)( Ie2)

WHEREX/2,,?:y/b:C:z/d

2: 1/2 LENGTH) b: 1/2 BEAM, d: DRAFT

2:8.OFT. b:0.75FT. , d:l.OFOOT TOTAL ©,

RATIO 22/d:16.0

TRANSVERSE

/

/

N"-4

/

/

/

'I

\

/\

/

/

\

,'

al%

/

_-/'---©

DIVERGENT

/

WAVES ONLY

N

!

7(...d \

\

/

/

0.15 020 0.25 0.30 0.35 0 40 0.45 0.50 0.55 0.60 SCALE OF FROUDE NUMBER F

FIGURE 3.

BREAKDOWN OF THEORETICAL WAVE RESISTANCE FOR A

0.9

0.8

0. 7

0.6

IL.

0.5

U LII U

z

4 I-. U,. U) Ili

0.4

-J 4

I-0

0.3

R- 1082 0 DD692(LONG HULL) DESIGN A X DESIGN B . A

x

:

:.,

'X)(

A DESIGN A

I

cf'

L £ DO 692 (LONG HULL) DESIGN B: FOR DESIGN B FOR DO 692

AND DESIGN A SCHOENHtRR FRICTIONAL COEFF.

-L.

02

03

0.4 0.5

06

07

Ft

'U

0.6

0.5

0

IL' N

-j

4

0 0,4

0

'C IL IL.

0.3

U

z

4

I.-(I) In U

4

a

(I, U 0. I DESIGN A X DESIGN B R - 082 0,2

03

0.4 0.5 0.6 0.7

F:

U

FIGURE 8.

RESIDUARY RESISTANCE COEFFICIENT AS A FUNCTION OF FROUDE

0.3 0.2 0 3 2 0

FIGURE 9.

SIN KAGE AND TRIM DETERMINED FROM TOWING MODELS IN CALM WATER

R 1082 DESIGN A a a a a £ xa a A

x-,x

I B DESIGN SINKAGE

aX

S a

aX

ax1,X

.

5'

. .

S DD692

0

S

x

S S (LONG HULL) o 0D692 (LONG HULL) DESIGN A X DESIGN B

I

.

DD692 (LONG HULL)

.

S

I

)(4'

S a a TRIM a a . a a

)

A

x''

S

x

X"

A

/

a

x

£ A DESIGNA DESIGN B -Is

Xaa

a a 0.2 0.3 0.4 0.5 0.6 0.7 FROUDE NUMBER 0.2 0.3 0.4

05

06

01 FROUQE NUMBER

zo

In 0.1

1.6

0.4

0 0

FIGURE IOa.

PITCH AMPLITUDES AS FUNCTION OF FROUDE NUMBER FROM

TESTS OFMODELS 0F692(LONG HULL) AND DESIGN A DESTROYERS

FOR X/L=O.75

'U 0 I.-.J 0 4 U > 4 'U

I

U -J a, 0 0 1.2 0 X/L :0.75 HE AVE

02

03

04

FROUDE NUMBER

FIGURE lOb.

HEAVE AMPLITUDES AS A FUNCTION OF FROUDE NUMBER

FOR X/LO.75

R - 1082

05

06

07 DESIGN A

X/L:0,75

PITCH 0 FOR WAVE RATIO: HEIGI4T 1/40.8 TO LENGTH 01 0.2

03

0.4

05

0.6 0.7 FROUDE NUMBER 0.I 0

1.2 wuJ

!.

0.8

4

WLLI >

44

w 0.4

go

0.1 02. 0.3 0.4

05

06

01

FROUDE NUMBER

FIGURE lOc.

PITCH AMPLITUDES FOR X/LI.O

0.1

03

04

FROUDE NUMBER

05

FIGURE lOd.

HEAVE AMPLITUDES.FOR X/L=I.O

R- 1082

ODD 692 (LONGHULJ DESIGN A

HEAVE

2.8 2.4 2.0 1.6 1:2 _{0.8 0.4} 0

I'

44II

II

o DD692(LONG HULL) DESIGN A X/L :121 01 02

03

04

05

06

FROUDE NUMBER

FIGURE IOe.

PITCH AMPLITUDES FOR X/L=I.25

FIGUREJOf.

HEAVE AMPLITUDES FOR X/LI.25

0DD692(LONG HULL) DESIGN A l.2I

01

PITCH

"H

:I25 H A

A'

0 01

02

0.3

04

05

06

07

FROUDE NUMBER 2.8 2.4 w 2.0

a

-J 1.6 1.2 -J

0 a

Q8 _0.4

UNCLASS IFIED

Security Classification

Security Classification

DOCUMENTCONTROL DATA.. R&D

(Security cta.eiflcetion oI title body of abetted and indexiná annotation miset be entered islian the overall report I. cla.eili.d) I. ORIGINATING ACTIVITY (CooràtI author

Davidson Laboratory, Stevens Institute of Technology

2á. REPOR1 1iCuR1TY C

LASIFICATiON-Unclassified

zb. GROUP

3. REPORT TITLE

RESISTANCE AND SEAKEEPING.PERFORMANCE OF NEW HIGH SPEED DESTROYER DESIGNS

4. DESCRIPTIVE NOTES (Type ol report and inclueivö date.)

Final

S. AUTHOR(S) (Laet ninie. (Stat name, initial)

Breslin, John P. Eng, King S.

6. REPORT DATE

-June 1965

7a. 1OTAL NO. OP PAGEC

33

lb.

NO.OF REPC

1k

8.

CONTRACTORGRANTNO _{Nonr 263(10)}

b. PROJECT NO. DL Project 2738/060

c.

d.

Se ORIGINATORSREPORTNUMBER(S,)

Report 1082

-Sb, QTI.IEflRPORT NO(S) (Aàyothernumbere that majr be à.a1,.d

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11. SUPPLEMENTARY NOTES - IzsPoNsóRING MILITARY ACTIVITY

Bureau of Ships and the Office of Naval Research

*3. ABSTRACT

-Results of calm water resistance. testsfor tWo new destroyer-designs are compared with data for the DD692 Class (long hulL) Heave and pitch measurements in three.wave lerigths,.which are reported for the better of the two new designs, show its marked superiority over 692 in all but the very low speed range. A check of the roll characteristics shows that the

gain in seakeeping performance is obtained at small sacrifice in roll stability which may be overcome by design refinement. It is concluded that this brief study has evolved a highly practical destroyer form which has markedly reduced heave and pitch with some increase in resistance at low speeds and a reduction In resistance at high speed. This form, which merits cOnsideration for additional study, holds greater seakeeping potential

for ASW missions than any other advanced surface-ship concept previously

studied.

D Li

I JAN 4

KEY WORDS

Hydrodynamics: seakeeping, wave resistance

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