Development and model tests of an efficient planing hull design

April 1959

lab.

v.

ScheepsbuwuJa

Technische HogschooI

Deift

Eugene P

Clement

DEVELOPMENT AND MODEL TESTS OF AN

"EFFICIENT PLANING HULL DESIGN

HYDROICHANICS LABORATORY

RESEARCH AND DEVELOPMENT REPORT

Report 1314

çHiEr

HYDROMECIIANICS

0

AERODYNAMICS STRUCTURAl. MECHANICS APPLiED

MAThEA1IGS

0

PRNC-ThB-M8 (11-561

DviLOPMENr AND MODEL TESTS OF AN

EFFICIENT PLANING HULL DESIGN

by

Eugene P

Clement

ApriI. 1959

Report 1314

Fn

g

7

NOTATION

Symbols

Projected area bounded by chines and transom, in plan view

Breadth over chines at any point; also, buttock

Mean breadth over chines, A/L

Breadth over chines at transom ximum breadth over chines

Froude number based on volume, in any consistent units

v/ VjlT3

Acceleration due to gravity

L Overall length of the area, A, measured parallel to baseline

LOG Longitudinal enter of gravity location

P Effective power, ft-lb/sec

R Total resistance

S Wetted surface, area of

Density ratio, salt water to fresh water

v Speed

V Speed,\ knots

w Density of water (weight per unit volume)

WLc Intersection of chine with. solid water, forward of

0 percent L, ft

WLK Wetted length of keel, forward of 0 percent L, ft

WL3p Intersection of chine with spray, forward of 0 percent 1, ft

Angle with, horizontal of tangent to mean buttock at stern,

deg

Dead rise angle of hull bottom, deg

A Displacement at rest, weight of

T

Trim angle of hull with respect to attitude as drawn, deg

Model

Ship

Value at rest

r

Subscripts

111

ABSTRACT

A hull form for a stepless planing boat was designed, based upon an analysis of the results of resistance tests of a number of previous designs, and also taking into consideration the features desirable for good steering qualities and good

rough-water. performance. A model was built and tested, and the

results were compared with the resIstance data from designs

which had been previously tested at the Model Basin. This

com-parison showed that the new design has appreciably less

resist-ance than the earlier designs at all except very low speeds.

The new design was also tested at a wide range of hull loadings and LCG locations, and these results are presented.

ITRODUCT ION

References land 2'resented methods of analyzing.and comparing the.

performance of stepless planing boats. Among the methods proposed was

that of testing each planing hull model at a standard condition of hull

loading .and LCG location and then correcting the results of each model

test to a standard displacement. The purposes of this approach were. to

eliminate the effects of several important variables on performance so

that the effects of the remaining differences could be distinctly seen.

Subsequently, a..,number of planing hull models were tested in the proposed,

manner, and as:anticipated, it was possible to draw conclusions as to the

effects on performance of some of the major hull form parameters.

Subse-quently a planing hull Was designed, based on the conclusions which had

been drawn. A model of this design has been tested and the results are

presented in this report. .

A comparison of the performance of the new design with that of all

stepless planing boat designs previously tested at the Model Basin shows that the new design has appreciably less resistance than any of the

others. The new design was also tested over a wide range of hull

loa4-ing and LCG location, and. these results are presented.

DESIGN PROCEDURE

After comparing the resistance data from standard condition tests

of a number of planing boat models, and considering the features

desir-able for good steering qualities and good rough-water performance, it

was concluded that a high performance stepless planing hull should have the following features:

A narrow stern with the transom width equal to about 65 percent of the maximum chine width, and with the point of maximum chine width located at about 6Q - 65 percent of the length forward

of the iransom. Fur a hull having a ratio of length to average

beam of 5, this results

in

the line of the afterbody chine, in plan

view, making an angle of about 5 degrees with the centerline.

Little or no bottom twist over the after half of the hull

length.

Relatively high deadrise at the transom - at least 10

degrees.

Straight sections aft and convex sections forward.

The resIstance comparisons made showed a consistent superiority

for the narrow-stern hulli over the wide-stern hulls. The reasons

for this seem fairly clear. At low speeds, a narrow stern will

pro-duce less eddy-making resistance than a wide stern. Furthermore, the

fact that the afterbody chine makes an appreciable angle with the hull

centerline has desirable consequences... At low speeds, the pressure of

the water against the si4es of the afterbody has..a forward component,

which reduces the resistance. At intermediate speeds thewater

flow-ing from under the bottom along the chines has a velocity component

away from the hull. This results in reduced side wetted area and

therefore in reduced frictional resistance. At high speeds, as is

well known, the bottom area near the transom contributes little to the

lift, but adds to the frictional resistance. The region nOar the

for-ward boundary of the wetted area is much more efficient in the

produc-tion of lift. Accordingly, the more efficient planing bottom is one

which is wide forward and narrow aft. A narrow stern is also

con-sideredto be much superior to a wide stern in the dangerous

following-sea condition. The hazard in a following -sea iS that the stern will

Ibe lifted and the bow depressed to such an extent that the convex bow

1JjbuttoCks

encounter the water at an a ttitude that produces a downward

orce. The boat may then broach and be in danger of capsizing.

A

narrow stern has less buoyancy, and hence, less tendency .t be lifted

than a wide stern. it was shown in Reference 2 that a large amount of

twist gave high resistance. Also, analysis of the steering process

indicates that a relatively high deadriseat the stern is -desirable.

Forward of amidships, the dea.drise should increase rather rapidly to

an angle of about 35 degrees at Station 1, in order to give an

effi-cient entrance and reduce pounding in waves. These requirements are

satisfied in the present design by making the deadrise constant at

12j degrees from the transom to 40 percent of the length, and increas-ing the deadrise. from there to a value of 36 degrees at 90 percent length.

The after half of the bottom (which is, roughly speaking, the plan-ing area) is in the present design, essentially a simple prismatic

sur-face0 As far as is known, there is no advantage in introducing the

cOmplexity of either convex or concave sections in this region. It is

cOnsidered that cOnvex bow sections will produce the least pounding, and

accordingly the sections forward of amidships are made convex.

Iffec-tive spxay strips will be required with the convex sections in order to control the spray height.

The hull lines which were developed according to the above

reason-ing are shown in Figure 1. The ratio of length to average beam, (I/Ba)

was selected to be

_5,

corresponding to a planing boat having a gross

weight of about 60,000 pounds. (See Reference

10)

It is considered

that the lines presented in Figure 1 are suitable for powered boats of

a wide range of sizes, if the length..beam ratio is adjusted to suit the

particular boat size.

TEST PROGRAN AND RESULTS

A wood model 8 feet lông was built to the lines developed. The

model was first tested at the Model Basin's standard condition for

plan-ing boat designs. This is at a value of area coefficient

_(WV?!3)

equal

to 70, and with the LOG located at 6 percent L aft of the centroid of

the area A, The results are presented in the design data sheet,. Figure 1.

In Figure 2, the resistance data are compared with data from 8tafldard

condition tests of the four designs reported on in Reference 2. It can

be seen that the new design has less resistance than the others at all speeds except the lowest,

The new model was also tested over a wide range of loadings (area

coefficients of

5, 6,

7, 8, and 9), and at 3 LOG locations (OG at the

centroid of , and at 5 percent L and 10 percent L aft of the centroid).

The results are presented in dimensionless form in Figures 3 and 4. The

resistance data have all been corrected to 100,000 pounds displacement, using the 1947 ATTC friction coefficients, with zero roughness allowance.

Presented in this manner (i.e., in terms of dimensionless coeffi-cients based on displacement), the curves can be directly compared tO find the dimensions and LOG location of a boat, of given gross weight,

which will have the least resistance. In effect, each resistance curve

represents the performance of a boat which will answer the purpose of a particular design problem, and the lowest resistanOe curve represents the 'boatof particular size and LOG location fOr minimum resistance.

The resistance data are plotted in a different form in Figure 5, to show the effects of both LOG location and area coefficient on resistance, for several values of the speed coefficient.

Figures 3 and 5 will give valid indiOatiorxs as to the optimum values of LCG location and area coefficient for a. wide range of values

of displacement, both above and below 100,000 pounds., Accurate curves

of resistance versus speed for boats having displacements other than 100,000 pounds, can be determined by means of the data available in

Figures 3 through 6, Assume that the problem is to design a 60,000

pound boat (so that the present data for a length-beam ratio of 5 are

applicable), and that the top speed is to be 38 kflots. It is desired

to determine the optimum hull size and LCG location, and also to

con-'strüct an accurate curve of rdsistance versus speed for this boat.

From the auxiliary graph of Figure 7, it is found that the value of F, co'responding to 60,000 pound displacement at 38 knots is 3.65.

Next, Figure 5 indicates that at values of Fn. 3.5, the aftmost LCG

location of the three locations represented will 'give the least

resistance.. Next, Figure 3(c) indicates that an area coefficient.

value of 8 will give relatively low resistance throughoutthe' speed

range. A further reduction in R/A at value,s gf F less than 3.3

would be obtained by adopting a value of A/s2/3 equal to 9. However,

this would require a 7 percent increase in length and beam of the boat (which wóüld appreciably increase hull weight and cost) and therefore

does pot appear 'to be justified. Accordingly, the values selected are

A/92/3 = 80, with the LCG at 10 percent L ft of the centroid..

Knowing that .A/,2/3.

_8,

_{and L/BA 5, the length of the boat can}

be determined as follows: ' .. A

L'8

LL/5

- L2

__ -

-74- =

fr

-__

Also (v)2t3 ₍

OOOO )2/3:

(60,000)2/3 ].533 95.8 4 . 16 And i? 58'° 95.8 . 3832 Then L _61.9'

The process of determining the resistance of the boat at a speed

corresponding to 3.0 will be indicated next, The process can be

repeated for a number of speeds in order to construct a complete curve

of resistance versu speed.

From Figure 3(c), R/4 equals 0.U85. Then the resistance of

the standard 100,000-pound boat equals 100,000 x 0.1185

U,850

pounds. . ,

From Figure 4(c),, S/v2/3 equals 4 79. Then the wetted sr,face,

S, for the 100,000-pound boat is: 4.79 v/

i00000

/

64

4q79 134.7 645 square feet.,

3. From Figure 6, interpolating between the available curves

for an area coefficient of 8, the mean wetted length for the 100,000 pound boat equals 42 feet.

..3 16O,00o

,#.Y

100,000

4, The linear ratIo between the 100,000- an 6Q,000-pound boats

is eoual to:.

=

= O8434

5, Knowing the resistance, wetted surface, and mean wetted

length for. the 100,000-Pound boat, and the linear ratio between the

100,000-and 60,000.pound boats, the resistance of the latter can readily be calculated using the method described in Reference 3, and

n the standard works . on. nAval architecture0

FUTJRE WORK

Since the comparison in Figure 2 shows that at the lowest spee4

the present design has more resistance' than the other designs, it is

intended to test a revised model having slightly smaller waterline

entrance angles0 The modified hull form will alw consist entirely

of developable: surfaces. It is expected that this change will

re-duce both resistance and bow spray at low speeds0

RFERNCS

-'. 1. Clement, L P0., "Analyzing the Stepless Planing Boat,°

K David Taylor Model Basin' Report 1093 (Nov 1956).

2. Clement, E. P., and Kimon, P. 1l., "Comparative Resistance

Data for Four Planing .Boat Designs," David Taylor Model Basin

Report 1113 (Jan 1957)0

3. Morray, Allan B., "The Hydrodynarnics of Planing Hulls,"

Transactions of the Society at Naval architects and Marine Engineers,

Vol. 58 (1950), pp. 658

692.

a.

.0 1 0.1 0.0 0.0

Figure 1

2 1 7 6 5 4 2 0 lOP ag1 V aIr S0T I1I5

-54 -U 1Sn. 7 lie 1 11 FORM CHARACTERISTICS 'S LINES MODEL _{A' 12.80 sq ft L. 8.00} ft. 9s1.600 rt NOI(L 41St Sni. ICACI IS 110111

PLANING BOAT DESIGN DATA SHEET

DAVID W. TAYLOR MODEL BASIN

FULL SIZE A'942.52 sq

ft L- 68.08 ft .13.?3 ft FlOURS 1 March 1959 11 SISIP l.S. Sn. W TI lflt 1* lOSS .lmn lOtion .s a a ioii as ro an 0 0 MODEL DATA TEST No. 0 BASIN HIGH-SPEED BASIN

BASIN 51ZE2968'x21'X(10' & 161 DATE OF TEST

4 November 5? WATER TEMP 72 APPENDAGES SPRAY STRIPS TURBULENCE STBA NONE MODEL MATERIAL WOOD MODEL FIMSI4 I'AINT 7.50 9.7? 20.31 6.60 4.60 5.70 15.66 26.1? 5.70 3.40 4.60

a'

7

6 %L GENTRCC OFA AFT vi's OF C. LCG rise

Resistance and power corrected to 100.000 lb using

1947 A.T.T.C.

Model-Ship Correlation Line with zero roughness allowance

TEST NO. lb , Ibi. -s's MAIGMUM SIESLE F,,9 7: (VLi..5 CO APT OF CONTROlS oco LCG % L 153.9 100.000 7.00 5.91? 0. 20° x stern fl.20 6%L 42.8 40 -20 00 80 L/B,° B,/B,'o 4.092 .644 -60

__.11lIli

S CEN AT48.8%L ROID OF A

-40 2. 20 O

MEAN BUTTOCK

I!_J

DTMB MODEL 4667 HIGH SPEED PLANING B0i I TEST CONDITIONS DENSITY RaTIO. SW/FW, 1.0284 0 10 20 30 40 50 60 70 80 90 100 PERFORMANCE CHARACTERISTICS F,, 1 2 3 5 1 2 3 4 5 F,, 'P '1° Tie 'P 'P 0.1 0.1

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uueIuuVSuu(u4 u.n U,.,' mile JV.S14U Inn '4 ReBietance corrected to 100,000-lb

diep.,

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friction

coefficiente

with, zero roughneaa

allowance. A/V'f.

_L,ft,

_for

_100,00 lb

dispi.

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and

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F,

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Figure

3a

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at

Centroid

of

A 8

Figure

3b

_-

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at

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Percent

L

Aft

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of

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F1, _s

vNjvr

1 3 4 S F., Figure 4a LCG at Centroid of A

U

10 9 .1 8 7 6 I' I' _-Cr 4 3 5 A/V0

_L,ft,

-lb

4ispl.

for

58.00 63.5? 68.65 73.38 77.87 100.000 2 6 7 8 9 1 0 2 3 4 5 6

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.

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diapi.

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Figure

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at

10,

Percent

L

Aft

of

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of

A

13 0 0 a 7 6 1.. 2 3 5 6 F11, ₌ -- - orpols. 3 Porpo ee F11, ₌ 1 2 3

..

4 5 6 2 *fv

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_for

_100.0'.

lb

dlapl.

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r?t...

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5:,....:

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aft

or centrot6 Of £ ft a ft ft fl 1. I, ft ft 6 9 5 6 8 P

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27+

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Figure 5 _- Resistance _versus Area Coefficient

14

5-

6 7 6 7 A A .1 .11 .09 .0 .17 .1 .1 .11 .09 .16 .1 .12 .15 .13 .16 .14 .12

I-J

Figure 6 - Mean Vetted Length versus Wetted Surface, 100,000-Pound Displacement

100 90 80 70 60 50 0 40 0 30 .U : 5 7 9. 20 or 100,000-lb diepi

wetted surface, 8, equals S/v* x 134.7.

10 0 0 100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 Wetted surface, sq ft

7 6 5 2 1 o o

0

0

0

o o

0

oco

co

DIsplacement, lb (sea water)

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0.

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ID

0

0

I 4 ID

/7

10 20 30 40 50 60 70 80 90

bc

V, knots Figure 7 - Variation of Volume Froude Number with Speed and Displacement 4 Pnv 3

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