A study of the sea behaviour of a mariner class ship equipped with anti-pitching bow fins

Technische Hog .sdio

Delfi

HYDROMECHANICS A STUDY OF THE SEA BEHAVIOR OF A MARINER-CLASS

SHIP EQUIPPED WITH ANTIPITCHING BOW FINS

0 by AERODYNAMICS Ulysses A. Pournaras 0 STRUCTURAL MECHANICS 0 HYDROMECHANICS LABORATORY RESEARCH AND DEVELOPMENT REPORT

APPLIED MATHEMATICS

October 1958 Report 1084

s,

October 1958

A STUDY OF THE SEA BEHAVIOR OF k MARINER-CLASS

SHIP EQUIPPED WITH ANTIPITCHING BOW FINS

by

Ulysses A. Pournaras

otic

Report 1084 '

ABSTRACT TABLE OF CONTENTS Page 1 INTRODUCTION 1 GENERAL 1

SHIP AND MODEL DESCRIPTION 1

FINS 5 INSTRUMENTATION 8 TEST PROGRAM 10 TEST RESULTS 11 PITCH 11 HEAVE 12

PHASE LAG OF HEAVE REFERRED TO PITCH 12

POINT OF MINIMUM VERTICAL MOTION 13

VERTICAL MOTION AND ACCELERATION 13

AVERAGE BENDING MOMENT OF FIN NO. 1 23

COMPARATIVE PITCH REDUCTION OF FINS TESTED 23

SUMMARY OF TEST RESULTS 27

DISCUSSION OF RESULTS 27 CONCLUSIONS 29 REFERENCES 29 i. ... ... , . .

LIST OF ILLUSTRATIONS

Figure 1 A Ship of the Mariner Class 2

Figure 2 Body Plan of Mariner-Type Ship,

Figure 3 Plan Views of Antipitching Fins 1 and 2 ₄

Figure 4 Views of kntipitching Fin 4 5

Figure 5 Antipitching Fins 6

Figure 6 Three Model Installations of Antipitching Fins 7

Figure 7 Installation of Instruments 9

Figure 8 _{Experimental Pitch Amplitudes As a Function of Wave Height 12}

Figure 9 Experimental Heave Amplitudes As a Function of Wave Height ₁₃

Figure 10 Experimental Phase Relationship Between Heave and Pitch 14

Figure 11 Computed Location of Point of Minimum Vertical Motion 14

Figure 12 Computed Amplitude of Vertical Motion Along Length of Ship 15

Figure 13 Computed Amplitude of Vertical Acceleration Along Length of Ship 19

Figure 14 Experimental Average Bending Moments Experienced in Waves by

Fin No. 1, 7 Feet off Centerline 24

Figure 15 Comparative Performance of Various Fin Configurations Tested 25

Figure 16 - Dimensionless Pitch Amplitudes 26

Figure 17 Dimensionless Heave Amplitudes 26

Figure 18 Phase Lag of Heave Referred to Pitch ₂₇

LIST OF TABLES

Table 1 Principal Characteristics of Mariner-Type Ship and TMB Model 4414 1

Table 2 Schedule of Tests Speed 10

Table 3 Schedule of Tests Wave Size 11

Table 4 Comparison of Pitch Amplitudes 23

.... . ... .. ... .. .... ... ... . ... ...

NOTATION

Fn Froude number

Acceleration due to gravity

Wave height measured from trough to crest, 2 r Ship length

LCG Longitudinal center of gravity

rm Wave amplitude

Period

V Ship speed

Dimensionless heave, anz/r.

Heave amplitude

Wave length

Dimensionless pitch, c/J ./Om

e Frequency of encounter in waves

ABSTRACT

The results of model tests performed to determine the feasibility of

re-ducing the pitching motion of the Mariner-type ship by means of fixed

anti-pitching fins at the bow are presented. A 20-foot self-propelled model represent-ing the final design of the Mariner-type ship was tested in waves with four anti-pitching fin configurations. Data are presented for both model and ship and are summarized in dimensionless form. The data are also used to compute the effect of the fins on the vertical motion and acceleration along the length of the ship.

INTRODUCTION

GENERAL

A self-propelled model of the Mariner-type ship with and without antipitching bow fins

has been tested in waves at the David Taylor Model Basin. Four fins were fitted to a Mariner model to determine the pitch reduction as a function of plan characteristics.

The model, fins, and instrumentation used for the tests are described, and the exper-imental results are presented and discussed.

SHIP AND MODEL DESCRIPTION

TMB Model 4414 with a linear ratio of 24.175, representing the final design of the Mariner-type ship, was used for the tests. The principal characteristics of the ship and the

model are given in Table 1.

TABLE 1

Principal Characteristics of Mariner-Type Ship

and TMB Model 4414

Item Ship Model

Length, 0.A. 563 ft 7% in. 23.30 ft

Length, B.P. 528 ft 6 in. 21.85 ft

Length, 25 ft 0 in. WL 520 ft 0 in. 21.34 ft

Beam, Max. Molded 76 ft 0 in. 3.14 ft

Draft, Load Line 29 ft 101/16 in. 1.24 ft

Displacement, Load Line 21,093 tons 3,252 lb

Block Coeff., CB 0.613 0.613

Load Waterplane Coeff., Cw 0.724 0.724

The model had been used in previous resistance tests and was modified to conform with the sheer forward of amidships. The forecastle deck and bulwark, properly scaled, were also added to the model. A solid watertight deck cover was provided throughout the length

or the model,

A photograph of the ship is presented in Figure 1; the body plan in Figure 2.

Figure 1 A Ship of the Mariner Class

Figure 2

Body Plan of Mariner-Type Ship

itali"

111111111MIL

se

111111101nt

RD-111114111.

24

filabgailEIL

awormumommols

lilEMMINE11111111.1

To. df Kn M.In 17 3nd e 20 16

IIIELIMEMMIONIL

glIMIIINAIRIIPOIS

rimeTeNTArtramBibm

ilge Keel race\\INIMMININVILIMIZINE

BulOark

"E-56.-0" 4 ..

mi

&wmilligigi.

i

/Dec %NMI*

Arilki

io 1 -co

.

10.1" -c`ti 0 Knuckle Line

1

4 8

11/11/.v

In

I El

IVAN./

1111111/4111

.:62.:::,.."vi

-1117rNIFA-ManIM,

/1.1/1111FiltSM

v II

l'FARBIESEIRINI

Milli

I/

De

WM/

1111111r9

== I

cklTo.

.44. 0 1 ''

'-II

44'-0" 744. -:.i.eiToLpino: tat fh7<erts, i

NEM

1Sattia;ti 'rinclik00at Trace

b. 1U

ck 1 -LO 1 1 A bv:

11111111.1111115L32,0MilIBIIIN

'

131

liONIESEIVEL,...iiriEBEEIF

2

E111111,,11111

_

L.

..

II

1111

2

III

24.-0. 16'-O"

...,

I'' A

'I

i

FR. '34

1111111111111

28 12 8

IIIIII

, ..

jarifflIWPWOMII

IMPRINEME

12 16

IIMPERNIERiltigit

mmaririTABITITA:

Nil

Keel 4

---.:

,W111/ Bile 20 24 26 .

Z., "'Cr

"fry

-20.5' Roof Chord 24'

hi-716'

1p Chord 0-1 Root Chord 22.8' Area: sq. ft. 0.8' 11 1-4- 11' --I. 22.8' Ni-at Tip

Fin Number 2s - Obtained from Fin Number 2, by cutting 5ft. off each tip, Pa S. Fin Number I

A

Fillet Fairing to Hull

c

Fin Number 2

Fillet Fairing to Hull

J

r /

Fin Plane of Symmetry at 3ft. above Base Line

Fin Plane of Symmetry at 3ft. above Base Line

Fin Area

- 0.022 Waterplane Area

Fin Number 2h - Obtained from Fin Number 2s, by drilling two 11/2 ft. diameter holes 2ft. aft of leading edge of fwd fin and two I I/2ft. diameter holes 2 ft. fwd of trailing edge of aft fin. Area and span of fins not changed.

Figure 3 - Plan Views of Antipitching Fins 1 and 2

= Tips off Centerline : 14 ft. Fin Area

9,1

Fin Area : 400 sq.ft. Waterplane Area

= _tf

-

_{I /3}

Fin Area

Waterplane Area - 0.022

Fin 620

Fin Number 4 14' + +

++

1 + ++

38' Fins separated by 1 ft.

Upper surface of fin tangent to baseline. Fin Area: 640 sq ft.

Fin Area _0.023

Waterplane Area Fin Number 4h

Obtained from Fin Number 4, by drilling five 1-ft

diameter holes on each fin as indicated in sketch.

Figure 4 Views of Antipitching Fin 4

FINS

The program consisted in testing several antipitching fins to compare their relative performance. The difference among the various configurations tested was one of plan

geometry. In_profile section all fins were essentially flat plates with faired leading and_trail-Lag edges. The intersections of the fins with the hull were fillet-faired. The principal char-acteristics of the fins are shown in Figures 3 and 4. Figures 5 and 6 show photographs of the various fins as installed on the model. Following is a description of the four types tested.

Fin No. 1 Swept Forward. This fin had a leading edge normal to the direction of advance, and a swept forward trailing edge. The purpose of the sweep was to reduce the load near the tips and, therefore, the bending moment at the root. The thickness of the fin was 5/8 inch, corresponding to the apparently unrealistic full-scale thickness of 15 inches. The

leading edge of the fin was at a distance aft of the forward perpendicular corresponding to

X

2.38 feet full scale. The chord plane of symmetry was at the ship's 3-foot waterline. The

.42.8.1 fin tip to tip, corresponded to nearly 41 feet. The plan area outboard of the hull,1e

A-R-r-was 2Lpercent of the load waterplane area. Fences were installed at both tips of the fin. These extended 18 inches full scale above and below the upper and lower surface of the

Fin No. 2 Twin Configuration. This configuration was rectangular, the span measure-ment corresponding to 38 feet full scale. The chord plane of symmetry was as in the previous

case. The two fins making up the configuration were identical, had a dad corresponding to _X 11 feet full scale and were separated by a distance corresponding to 9.64m4.- The purpose

of the separation was to facilitate the flow around the fin by offering a passage through the

5

fin.,

-F, Fin No. 1 Fin No. 2 iIP 21-6360 NP21-6479i Fin No. 2h ma.

-'Fin No. :3. 4,444.-zeb4i0

61,

, 411.111111,

-Fin No. 4

Figure 5 Antipitching Fins

"Twin" Configuration

Figure 6 Three Model Installations of Antipitching Fins

7

A..94

middle of the overall chord. Such flow relietwas considered desirable in view of previous

experience with antipitching fins at the Model Basin.1 Tigies, similar to those of Fin

No. 1, were also fitted. The plan area of the configuration outboard of the hull was again 2.2 percent of the load-waterplane area.

Fins No. 2s and No. 2h were obtained by modifying the plan of Fin No. 2. Fin No. 2s was obtained first by reducing the full-scale span by 10 feet so as to make the tip to tip distance 28 feet, and the plan area was reduced to 1.4 percent of the load-waterplane area. Fin No. 2h was obtained next by drilling holes corresponding to a full-scale diameter of

18 inches, 2 feet from the leading and trailing edges of Fin No. 2s, port and starboard. The purpose of testing these modifications was to investigate the effects of a further reduction of Rlanarta,1 and the possibility of decreasing the adverse effects of fin vorticity experienced when the fins approach the surface. Such vorticity effects are considered structurally

uncle-._

sirable. Tip fences were retained in both of the above modifications.

Fin No. 3 Dihedral Configuration. This configuration retained the plan geometry of Fin No. 1, and was obtained by rotation about the root chord. The dihedral angle was 30 degrees. The purpose of this configuration was to investigate the effect on slamming of

the wedge entrance so formed. It was for this purpose that the dihedral angle used was as

large as 30 degrees. This configuration was not fitted with tip fences.

Fin No. 4 Triple Configuration. This configuration was rectangular in plan, and con-( sisted of three fins in series each corresponding to 28 feet by 12 feet. The plan area

out-board of the 3-foot waterline was 2.3 Percent of the load-waterplane area. In this case, how-ever, the upper surface of the fins was attached to the underside of the keel forward, with

more support provided by two thin struts, port and starboard. The middle fin had a clearance

corresponding to 1 foot from either of the forward or after fins. The purpose of testing this configuration was to investigate the effects of deeper fin submergence on fin vorticity. Tip fences were installed in this configuration.

A modification, Fin No. 4h, was obtained by drilling holes of a full-scale diameter of 1 foot on both sides of each of the three fins.

INSTRUMENTATION

Direct data obtained from the model tests included wave elevation, strain, and pitch

and heave amplitudes. All data taken were recorded on an 8-channel oscillograph recorder.

hew , Gyroscope. (Pitch) ,31.7 Bow Accelerometer Bow Accelerometer (Heave and Pitch)

Propel ter Drive Motor

Propeller Shaft tachometer

-Stern Accelerometer (Heave and Pitch)

Figure 7- InstallatiOn of Instruments

Not shown in this phOtograph is. a 'heave measuring potentiometer fitted at the towing pantograph,,:.and a surge potentiometer at the guide-line pulley..

it ; 4 -1'

-Wave data were obtained with a capacitance-type, partially submerged, wire probe. Pitch

data were obtained with a gyroscope located amidships. Heave data were obtained with a

linear displacement potentiometer installed on the moving arms of a special pantograph at the

LCG. Pitch and heave data were also computed from direct measurements of the sum and the difference of the instananeous accelerations recorded by two vertical acceleromictrs located at equal distances fore and aft of the LcG. Motion data were also obtained with a 35mm movie

camera.

The principal fin configuration, Fin No. 1, wasequipped with two bending flexures on each side, to obtain data on strain due tobending moments experienced by the fin in waves.

Each flexure had a complete four-active-arm bending bridge. The flexures were calibrated

prior to testing.

In addition to the instrumentation described above, the model was equipped with an electric motor driving the propeller, a propeller shaft tachometer, an independent vertical accelerometer located at the bow, and an angular displacement type potentiometer for surge data.

Figure 7 shows the layout of the instruments.

TEST PROGRAM

The tests were conducted at a model displacement of 2699 pounds, corresponding to 17,505 tons for the ship. The draft was 12.4 inches even keel, corresponding to 25 feet full

scale. The tests originally called for a displacement corresponding to 15,870 tons at a mean

draft of 23 feet, with a trim of 4 feet by the stern. Tests at this load condition, however were

discontinued because the model without the fins exhibited frequent forebody emergence,

occa-sionally extending to more than one-half the ship's length. The design displacement of the

Mariner is 21,093 tons at a draft of 29 feet 10 1/16 inches even keel.

Tables 2 and 3 give the speed and wave size schedules, respectively, of the tests.

TABLE 2

Schedule of Tests Speed

Speed, knots Fn Model Ship 0 0 0 1 4.82 0.065 2 9.64 0.129 3 14.46 0.191 4 19.28 0.255

BLE 3

Schedule of Tests Wave Size

The radius of gyration was established experimentally at 25 percent LWL

pitch period of the model for the load condition corresponding to 17,505 tons full

1.44 seconds. The addition of Fin No. 1 increased the natural pitch period to I.

The experimental results are presented in Figures 8 through 15. The results include the experimental heave and pitch amplitudes and phase angles, the computed location of the

point of minimum vertical motion, the vertical motion and acceleration of any point along the length of the ship, and the computed values of the bending moments experienced by Fin No. 1

in waves. All dimensional results are presented in full scale and are summarized in the

con-ventional dimensionless form. The pitch reduction effects of the various fin configurations tested are also presented.

Because of the frequent propeller emergence experienced during the tests with and without fins, propeller rpm and surge data were erratic. The presentation of these data has,

therefore, been omitted.

PITCH (Figure 8)

Pitch amplitudes shown are experimental. Linearity of wave

ileigb/ at constant speed and wave length was found to hold within the wave-height range of the tests (the highest waves were 1/30 of their length). The data are presented in graphical

form, showing the amplitude of pitch per unit of wave height measured from trough tocrest,.

Pitch amplitudes for wave lengths not included in the direct presentation can be obtained by

interpolation. It will, however, be necessary to perform the interpolation graphically, as

linearity assumptions involving the wave length are not valid.

TEST RESULTS 11 . The natural scale was 59 seconds. -As waves ilL Alh Model Ship

Length, ft Height, in. Length, ft Height, ft

____J

15 3,4.5,6 360 6,9,12 0.703 60,40,30

20 4,6,8 480 8,12,16 0.937 60,40,30

25 5,7.5,10 600 10,15,20 1.172 60,40,30

30 6,9,12 720 12,18,24 1.406 60,46,30

It was not possible to obtain the natural heave period because of the limitations imposed by the size of the model and the width of the test basin.

0.35

10

Wave Length.= 600 ft;.

15 20

Ship Speed in knots

20 t , 4,---,-,-.--1 ,

,-11 1 , 1 i' Wove Li gth=. 360 _ _ tt. 1 , 1 1 , I

EMI

III

,

MI

MEI:

MI!

Wave

Mill

sit

tii

, Lengrttl =480, ft.

---i_

ILL U.

111

gres.

AITIIIIIIIII

El 0,

-Wave Length= 720 ft: Without 1 With Fins 1

--L

Legend

---Fns ,,---,

Ili _L-j 'rE 0.3 0.25 > a) 0.2 0.30 10 0.25' 0.20 m, 0.1 51 ca. 0.10 8 5 10 15 200 10 .15 20 Shp _{Speedin knots}

Figure EXperimental Pitch Amplitudes As 41 °Fuhc pion Of Wave Height

HEAVE (Figure 9),

Heave amplitudes shown are experimental. Linearity of heave with wave height at ,constant speed and wave length was found la hoid_within.lbeAvav.e.-height.razge, of the test,

as in the case of pitch. The data are presented in graphical forth, showing the amplitude of

-heave per unit of wave height measured from trough to crest. Heaveamplitudes for wave, lengths not included in the direct presentation can be obtained bygraphical interpolationtl

PHASE LAG OF HEAVE REFERRED TO PITCH (Figure 10)

Values of phase lag ofheave referred to pitch were determined directly from the

exper-imental data. The variations in phase lag with wave height at constant speed_and wave length

remained within the estimated accuracy of record interpretation% It was then assumed that for

this model the wave hei ht had no effect on the base relation between heave and pitbh. Phase values for wave lengths not included in the direct presentation can beiobtained by

graphical interpolation 0.15 0.10 0.05 0 0 5

8

-5

13

Waye Length .480ft.

15

Figure 9 Experimental Heave Amplitude As a Function of Wave Height

I

20

POINT OF MINIMUM VERTICAL MOTION (Figure 11)

The location of the point of minimum vertical motion, (apparent_pitc_liing...axi,2 was

computed from experimental values of heave, pitch, and their phase relationship. In such amputations sinusoidal ship motion was assumed. Sinusoidal motion was verified to the

ex-",X4-14,4

tent that the pitch and heave amplitudes obtained directly from the gyroscope and

potenti-ometer were within 5 percppt of the values computed from the sum and differences of the

instantaneous accelerations of two equi-distant points fore and aft of the LCG. As the pitch

and heave amplitudes are linear with wave height, the point of minimum motion is independent

of wave steepness within the range of the tests.

VERTICAL MOTION AND ACCELERATION (Figures 12a through '!3d)

The amplitude of the vertical motion and the acceleration of any point along the length of the ship were computed from experimental values of heave, pitch and their phase relation-ship. Sinusoidal ship motion was assum9d. The amplitude of the vertical motion or accel-eration of an_y given point along the length of the ship is linear with wave height at constant

speed and wave length.

(Text continued on page 23.)

I. 3

,

3 3 Wove Length .720ft. ,

,

.--..., *--... Without Fins With Fins 1 Legend _ I 1 1 0.5 0.4 0.3 0.2 0.1 0 0.6 05 0.4 0,3 02 0.1 0 Wove Length 360 ft. 5 10 15 Wave Length 600 ft. 5 10 15 20 15 5 10 200

Ship Speed in knots

10

200

Ship Speed in knots

.

I

---100 80 60 -o 40 Li 20 60 _J a, 0 ₄₀ *CD 35 30 25 20 10 a 5 20 20 25 Wove Length 600 ft

Figure 10 Experimental Phase Relationship Between Heave and Pitch

LC

cZit,

/L-1 20

.

_.

_\

--

I---

..- -...-... ...

,

--l----ft 480

\

Wove Length 1 I -- .... ""

...\:.\\

11

riimm

/1111.1.111111 --..._.-- ....-s.

./dilii

\

\

( IIPPigalli

\

k

\

Wove Length 480 ft \V Wove Length 600 ft Wave Length 720 ft

5 10 i5 20 0 5 10 i5 20 0 5 10 is 20

Ship Speed ,n knots

Figure 11 Computed Location of Point of Minimum Vertical Motion

5 10 15 20

Ship Speed in knots

5 10 15 200 5 10 15

Ship Speed in knots

Legend Without Fins With Fins Wave Length 720 ft a) 0 .c 0 15 , I

11.2 1.0 0.8 1:16 4 CP

o2

t

oo ILO .173

2

0.8 4.) 0.6 41:0 :E. 0 13 08 cr 0.6

Figure 12 = Computed AMplitude of Vertical Motion Along Length of Ship

0.4 0.2

0

225 150 75 LCG 75

Distance from LC G in feet

LCG at 9.55 ft. oft of amidships-4.4M

15

Figure 12a "Zero" Speed

150 225 .41

/7L

, IT-- ., - Pt of M. Without Fins Fins Motion

i

1 ii 1"--,--, With 11 [ 1,__ I I i i .

A

...-, 1 . . _ i lib--. , . , i 1- -

'llillIngli

1 ' II 11 --, ave Length: 720 ft. 1 4

ii,

st

.

II

I

'Mr"

-... popi .... IIWave Length : 600 ft.

IIII

I 1 1

kiiimi

_gm

1 ..-.. ... ..,.., 0111P" ... J

is

- Wave Length : 480ft. ____L. 1 s 0.4 0.2 .0

1112 0.8 0.6 0.4 0.8 0.6 LCG at 9.95 ft. aft of amidships Figure .12b - 10 Knots

__I/tare

_-

_{< -}

,!ee4 /6.,4e!ie-e .//7/Weeerer,

'III

'Without Fins

With Fins --,_--- Pt. of Min 1 ,I

INI

-=-=---=--- Motion

t

,

ESE

inn

hi...1

..,

norw

_/A

PIM

II

I,

NENE

_

Wave Length,:' 720 ft.

M

_Mr

_.

,

Ell

lad

limn! to

memo

PRIM

111

Muffin in

Wave Lenijth: 600 ft.

--,---___

im arm

rm.

UM NM

ENE

11111111111"

=SU 1111M11111"

1 .1

INFAIMME111

Wave Length -:, 480 ft.1 225 150 75 LCG 75 150 225.

Distance from LCG in feet 0.2 0 a) 0 0.8 0.6 0.4 L2 1.0 0.4

1.2 1.0 0.8 0.6 0.2 > 1.2 1.0 .0 2 0.8 ci t 0.6 0.4 a0.2 0 o cc 0.8 0.6 0.4 0.2

LCG at 9.95 ft. aft of amidships i.-ó

Figure 12c - 15 Knots 17 L

kil

1111 b. Without With Fins Fins Pt. of Min. Motion + 1 1

74

...--,

I

-.,t-1

Wave Length : 720 ft. ...

.

4

,,

4

...

-..,,[101

NEE

-- -

-IIIIMIIIMA-- III

i Wave Length : 600 ft_

---,-..-

---

4--- .--- ---. Wave Length: 480 ft. 1 ; CD o 225 150 75 LC G 75

Distance from LCG in feet 150 225

0.4

r0

:

:

-6 1.0 2 0.8 0_6 0.4 ã0.2 I° 0 1.0 0 ;7- as 0.6

'N4111111

4_

11111

grAin.

az

1111111EMILIMI

MINNE Wove Length : 480 ft.

LCG at 995 ft. aft of amidships.* Figure 12ct 20 Knots

,

'... ; i

..

..--.... -.... --.-.., I Without Fins With Fins Pt. of Min. Motion

i

1

i

---Wove Length : 720 ft.

lrilplill

ri

_ImmI

in1111111111.11IPV

_{MMEITILINIPP0"}

.

illaill

-

-

-1111 Wave Length: 600 ft 225 150 75 L C G 75 150 225

Distance from LCG in feet

1.2 1.0 0.8 0.6 0.4 0.2 -:

-1.0 0.8 g.' 0.4 cz' 0.2 0

t 0.8

g. 0.6 0.4

; 0.2

1.2 0

Figure 13 Computed Air, ,ittide of Vertical Acceleration Along Length of Ship

5 LCG 75

Distance from LCG in feet

LCG at 9.95 ft. aft of amidships

19

Figure 13a "Zero" Speed

!! 4 Without Fins With Fins

---s., -. i Wave Length 720 ff.

III

li IRV.

_him

minpi

....

,

Wave Length 600 ft 11111

NE

_Pi

Wave Length : 480 ft. a' 0.8 0 o 0.6 °- 0,4 0.2 150 225 0.6 0 1.0 I I 1

1.6 1.2 0.f:1 cr. a) 0.4

i

; 2.0 1.6 4.- 1 2 c. 0 al- 0.8

; 0.4

--_c o 0.4 0 225 - 150 75 LCG 75 150 225

Distance from LCG in feet

LCG at 9.95 ft. aft of amidships---7 .-Figure 13b 719.Kiriots

kill

l' Without Fins - - _ ,

1611,-With Fins ,

11111111= -

_...

-

Mill

Wave Length; 720 ft.'

nor

um,

limb_

_gm

NENE

-

1

0,

iii

_in

' Wove Length : 600 ft,

24

II.

H

111111

III

.111

11,111A

II

wpm.

a,

" ow=

NE

;"ii

-11/11/E211 '

Wave Length:, 480 ft 0 2.8 2.0

>1.6

0 0.8 :

! 2.0 0.8, 0.4 2.4 2.0 1.2 0.4 2.4 2.0 1,6 1.2 0.8 .0.4

0

Figure 13c 15 Knots 21 LCG at 995 ft. aft of amidships--0. a ,

gm

Without Fins _ -

IIIP A

gm

11

,

15...

, With Fins

---EPP.

H _ ___

_

=Ill

Wave Lengthr6720 ft.

lir

II

MN

. '

` lila

Es

Irmo

immium

Wave Length : 600 ft.

lin

,

Mil

mg

,

Eng-

..,_ on=

,....

IN

, 1

mow ERE

Length : 480 ft. Wave ____ I 225 150 225 150 75 LC G 75 .

Distance from LCG in feet°

1.6 1.2 0 0. 0.8 0.

24 2.0 0.8 g 0.4 0 2.4 ° 2.0 4:1 O. 4-0 a, 0.4 0 F.', 2.0 1.6 O. 0.8 0.4 0 1.6 Wave Length : 600 ft. LCG at 9.95 ft. aft of amidships... Figure 13d 20 Knots N.

.

... ,

.

_, Without Fins With Fins ...-., --___ __. ....- ...--Wave Length: 720 ft. N.

.

...-.-

/

.

_..

..

.

./. -,-..e.

.

...,

.

.

_,

.... ....-..-- ...-_ -... -._ ...--,... ...-Wave Length : 480 ft. I I I 225 150 75 LCG 75 150 225

Distance from LCG in feet

TABLE 4

Comparison of Pitch Amplitudes

Fin symbols correspond to those listed in the Introduction of this report.

AVERAGE BENDING MOMENT OF FIN NO. 1 (Figure 14)

The average bending moment experienced by the fin in waves was determined from experimental strain measurements. The moments shown in Figure 14 are averages of the "up" and "down" values. The moments have also been averaged along the chord. The experimental strain records indicate that the bending moment of the forward flexure was higher than that of the after flexure at ship speeds above approximately 10 knots. This is attributed to the ar-rangement of the bending flexures, the talie'red plan of the fin, and the type of distributed loading.

COMPARATIVE PITCH REDUCTION OF FINS TESTED (Figure 15)

The amplitudes of the pitch with the various fin configurations tested are shown in Table 4 above. These are compared graphically in Figure 15. A more extensive discussion

(Text continued on page 27.)

23

Wave

Length

Speed

Amplitude of Pitch degrees per foot of wave height

feet knots No Fin Fin Fin Fin Fin Fin 1,i,9

Fin 1 2 2s 2h 3 4 4h 0 0.155 0.165 0.16 0.165 0.145 0.18 0.165 4.82 0.32 0.22 0.205 0.25 0.205 0.22 * 480 9.64 0.28 0.18 0.175 0.18 * 0.185 0.185 0.18 14.46 0.23 0.145 0.145 0.165 * 0.155 0.165 0.165 19.28 0.19 0.12 0.12 0.125 0.115 0.12 * 0 0.20 0.195 , 0.195 0.195 0.205 0.205 0.20 0.20 4.82 0.22 0.20 0.195 0.22 0.21 0.215 0.215 0.21 600 9.64 0.255 0.205 0.20 0.225 0.215 0.235 0.225 0.22 14.46 0.29 0.195 0.19 0.235 0.24 0.23 0.22 0.225 19.28 0.28 0.17 . 0.165 0.20 0.21 0.195 0.20 0.205 0 0.20 0.19 0.18 0.165 0.19 4.82 0.165 0.18 0.165 * 0.155 0.165 720 9.64 0.23 0.21 0.205 0.19 0.215 14.46 0.225 0.21 0.205 0.195 0.225 * 19.28 0.30 0.20 0.19 0.195 0.21 * _ 4 = 24'. A= , .0.s A =

c9;-*Test, not run.

' *

*

* *

*

0

Wave Height in feet

Figure 14 - Expefimental Average Bending Moments Experienced Waves by Fin No. 1. 7 Feet off Centerline

11 Speed-0 knots

10

knots*-15 knots* * Fulik-scale

5

knots*-Full Scale knot: L

A

Ili

0

111/111E

INTAL

-mum

speeds to nearest Wove Length 720ft Ifull-Scal.e _...1111 1 .

11111111111EEM

pp-.

120 ,

--Full-Scale Wave Length .600ft 1 1

AA

)40 80 520 !60 1

I IIIM4111111

dor

1 1

rig

.

ii

.41119 ,FF.

MP

Ell

-''

MIEMIEM

-- M___..., -_ _

Full-Scale Wove Length 480ft

KO

Eri

i

FANNIN

Iri-

II

111

12 1

-1820 1560 11300. 1040 780 520 1040 780 520 260 260 1560 0 4 8

-

in 24

1

0.3

0.2

1,1-Sc

Fu ale Wave Length 77"

1111111111111111

11

MINIM 11/11/E_

111111

IIIFull-Sca le Wave Length-48O ft

.25

20

Fult-Scale Speed in knots

Figure 15 = Comparative Performance of Various Fin Configurations Tested

e

1111:111M11

2h 3 4 II 4h I 2 2s

111

i

111

710MIECTAII

el (D

Fin

0

Fin

0

Fin (1) Fin Bare 1

IFu I -Scale Wove Length 720 ft 1

---.--Fin

. Fin

40 Fin

I

600 ft

0.3 0 0.2 0.1 0.3 0.2 0.1 0 5 10

1.6 0.8 0.4 1.6 Without Fins 1.172 0.937 0.703 1406 L ' Without Fins With Fins L-=1 406 1.172 ---...

/

.. -..._{-- ---..} -...-.. 0.937

_

0.703 With Fins

/

f=

1.406,./

/

/

/

/

z1 .... ...-

/

/

/

/

/

...

/

/

/

/

/

/

,"'"...-1.172 -... ... /.# ... -.. ...-0.937 0 010 0.20 0.30 010 0.20 030

Froude Number, Fn Froude Number, Fn

Figure 16 - Dimensionless Pitch Amplitudes

0 010 0.20 030 0 010 020 0.30

Froude Number, Fn Froude Number, Fn

Figure 17 Dimensionless Heave Amplitudes

0.

0.

IL:172

0.937

ot -o 12 CP 40 a-160 27 With Fins X

--i

= 4067 L ' . ...

...,

--"

/

we

K

1.172

-7.--7---

/

j,'0.937 N N. .,./ Without Fins 21,. 1406 L .41111 1.172 0.937 0.10 0.20 0.30 0 0.10 0.20 0.30 Froude Number. Fn Froude Number, Fn

Figure 18 Phase Lag of Heave Referred to ?itch

of the comparative performance of the various fin configurations is presented under

"Discussion of Results."

SUMMARY OF TEST RESULTS (Figures 16 through 18)

The test data are summarized graphically in Figures 16, 17, and 18, presenting pitch, heave, and phase angles, respectively, for the Mariner-type ship with and without antipitching

fins,

DISCUSSION OF RESULTS

The results of the model tests indicate the feasibilityof reducing the amplitude of

pitch of the Mariner by means of antipitching fins installed at the bow of the ship. The _X

numerical value of the full-scale pitch reduction, however, may be influenced by scale effects.

The tests at the lighter load conditions, corresponding to 15,870 tons and mean draft

of 23 feet with 4-foot trim by the stern, showed small differences of pitch and heave amplitudes

compared with the results of the tests at the heavier load condition. The general behavior of

the model in the regular tank waves was, however, much worse in the lighter condition.

Fore-foot emergence and slamming occurred frequently. This can be attributed to the shallow draft

of 21 feet forward, and possibly unfavorable phase relationship between the heaving and 80

pitching motions. The experimental data of the light load tests were not analyzed to the extent required for careful conclusions.

An important effect of fitting antipitching fins was theelimination of slamming in the conditions tested. Slamming of the ship without fins in the heavier load condition occurred in wave lengths near ship length, and at speeds between 10 and 20 knots. The effect of the

fins was to maintain a minimum forefoot submergence of about 9 feet. in waves up to about

1.2 times the length of the ship. However, fin skimming and emergence did occur at the longer wave lengths. Skimming of the fins apparently caused no visible violence. Emergence,

when referred to the uninterrupted wave surface, was limited to some length forward of the

trailing edge of the fins. The whole underside of the fins, though, remained wet from the

water drawn by the fins during the up-stroke of the motion. The strain records did not indicate

any disproportionate increase in bending moment as might occur during

slammittg_afterner-gence. This observation, of course, is not conclusive because many factors, such as relative frequencies, have not been considered. The dihedral fin was observed to_tp_zgater_the wa,ta.r

in a smoother way, compared with the other fins.

The effect of forward speed and wave length on pitch reduction is noteworthy. It will

be observed that the damping contributed by the fins attains its maximum effectiveness in reducing the amplitude of pitch when the ship operates in the near-synchronous range. At

very low and very high frequencies of oscillation (that is, at frequencies of encounter with

the waves far removed from the natural frequency of the ship in pitch) the effects of added

damping are generally small.

The fins have little effect on the phase lag of heave after pitch. The small changes of the phase-lag values, however, assume importance in defining the point of minimum motion and also the vertical motion of any point along the length of the ship. Figures 12a through 12d of the results show this effect clearly. Although the point of minimum motion changes location with wave conditions and speed, such changes are rather small. For all practical purposes, the apparent pitching axis remains in the vicinity of amidships. The particular fin is seen to cause a comparatively greater shift of the apparent

pitchingis mainly in the

forward direction. The amplitude of the minimum vertical motion_withAnclwithgaiins_i§

practically identical, except in the longer waves tested. The dominant effect of the fins is to

reduce the amplitudes of the vertical motion and acceleration at points away from the apparent

pitching axis. This effect cannot be overlooked when installing equipment that has operational acceleration limitations.

Figure 15 shows that the reduction of the pitching_motionby the various configurations

was practically the same. Some differences exist in the 600-foot wave length, but they are too small to assume significance. It can be concluded that the _plan area of the fin is an

impor-tant factor in pitch reduction. However, the effectiveness of antipitching fins can be also

improved by designing for a higher vertical drag coefficient. The effect of area on the

anti-pitching effectiveness of the fins may be brought out by comparing Fins No. 2, 2s, and 4.

29

Fin No. 2sLiming the smallest lan area shows reductions com arable to Fin No. 2. On _X the other hand, Fin No. 4, having the largest plan area, does not show any added improvement.

In establishing the geometry of the fins, one must take into account the vorticity generated by their motion. This arises from the pressure differences between the upper and the lower surfaces of the fin. Such vorticity can result in structural damage, such as recently

experienced by a Dutch liner.

It appears from observations during the tests that the severity of the hydrodynamic

loading imposed on the hull by the vortices shed by the fins can be lessened by: 11. Deeper submergence of the fins (Fin No. 4).

J 2. Greater fin span (Fin No. 1). Tip fences.

Relief mechanisms such as slots and holes (Fins No. 2, 4, 2h, and 4h).

To provide a basis for structural design, hydrodynamic bending moments were measured at one point along the span (Fin No. 1) corresponding to 7 feet off the centerline, full scale. These are shown in Figure 15 as a function of ship speed, wave length, and wave height.

In regard to the strength of the fins, the bending moments presented in Figure 14 should be treated with caution. Since the load distribution is unknown, it is not possible to derive

the values for the bending moment at the root. Theoretical slamming computations, however,

indicate that the bending moment due to slamming is higher than that predicted for the

quasi-steady state. Thus, the structural design of the fin should be based on loads experienced during slamming. The dihedral fin was observed to be the smoothest of the various configu-rations tested in respect to re-entering after emergence in the most severe wave conditions tested.

CONCLUSIONS

The results of the model tests indicate thatreduction of the pitching motion of the

Mariner ship can be obtained by means of fixed antipitching fins installed at the bow.

REFERENCES

N../ 1. Pournaras, U.A., "Pitch Reduction with Fixed Bow Fins on a Model of the Series 60,

0.60 Block Coefficient," David Taylor Model Basin Report 1061 (Oct 1956).

V

2. Szebehely, V.G., "Apparent Pitching Axis," Forschungshefte fur Schiffstechnik,

Vol. 3, No. 16, p. 184 (1956).

(

41,24.K.4 ,

4Z7r oe...c&- _/4.-freA1,4

1e74-7-..44

Areft,441.4t

4cc7t44 I11-.0 P: Aug. z i-m eeizzc

/41.04.,Ar

71.-e _{,-,-12Aeeyezu}

Conies

13 CHBUSHIPS, Tech Library (Code 312)

5 Tech Library

1 Tech Asst to Chief (Code 106)

1 Apo) Science (Code 370)

1 Ship Design (Code 410) 1 Prelim Des Br (Code 420) 1 Submarines (Code 525) 1 Minesweeping (Code 631) 1 Torpedo Countermeasures (Code 631N)

2 CHBUORD

1 Code ReD 3 1 Code ReD

2 CHBUAER, Aero 8 Hydro Br (Ad-3)

5 CHONR

1 ;Aath Or (Code 432)

2 :.lech Br (Code 438)

1 Naval Sciences Div (Code 460)

1 Undersea V. art are Br (Code 466)

1 CO, ONR, New York, N. Y. I CO, ONR, Pasadena 1, Calif.

I CO, ONR, Chicago 1, III.

1 CO, ONR, Boston 10, lass. 1 CO, ONR, Navy No. 100. FPO Box 39,

London, England

1 NAVSHIPYD NORVA 1 NAVSHIPYD BSN 1 NAVSHIPYI3 PTS1111

I NAVSHIPTD PUG

1 CU, SUR ASDEVDET, Key Nest, Fla. I CDR, USNOL

1 DIR, USNRL

I DIR, Langley Ado Lab, Langley Field, Va, I CDR, USN Air Missile Cti, Pond Mugu, Calif.

I CDR, USNOTS, Underwater Ord Div, Pasadena, Calif.

1 CDR, USNOTS, China Lake, Calif. 1 CO, USNtADL, Panama City, Ha. 1 CO, USNUOS, Newport, R.I. 1 CO, Frankford Arsenal Office of Air Res,

Appl Mech Cr, Wright-Patterson AFI3, 0.

1 DIR, Nall BuStand

1 BAR, Bendix Aviation Corp, Teterboro, N.J. 10 ASTIA, TIPDR, Arlington, Va.

1 Asst Secy of Def (Res 8 Engin) 1 DIR, Alden Hydra Lab, Worcester

Polytech lost, Worcester 2, Mass.

1 DIR, Appl Phy Lab, Johns Hopkins Univ,

Silver Spring, Md.

INITIAL DISTRIBUTION

Copies

DIR, Fluid 'tech Lab, Colombia Univ. New fork, N.Y.

1 CM, Fluid Mech Lab, Unit of Calif,

tterkeley, Calif. DIR, ETT, SIT, Hoboken, N.J.

1 E.V. Lewis

1 Dr. B.V. Korvin-Kroukovsky

1 DIR, Exptl Nan Tank, Univ of Mich, Ann Arbor,

Mick

1 DIR, Inst for Fluid Dynamics 8. Anal Math,

Ur& of Maryland, College Pak. Md. DIR, Hydra Lab, Univ of Colorado,

Godlier, Colo.

1 DIR, Hydra Res Lab, Univ of Conn,

Storrs, Conn.

DIR, Scripps lost of Oceanography, Univ or

Calif, Walla, Calif_

DIR, Fluid Much Lab, New York Univ, New York 53, N.Y.

1 DIR, Robinson Hydra Lab, Ohio St Univ,

Columbus, 0.

1 DIR, Hydra Lab, Penn State URIV,

dniversity Park, Pa.

I DIR. Woods Hole Oceanographic Inst. woods Hole, If

1 DIR, Hydra Lab, tidy of Wisconsin,

Madison 6, Wis.

1 DIR, rlydra Lab, Um,/ of Washington,

Seattle 5, Wash.

1 DIR, ORL, Penn St Univ, University Park, Pa,

1 1daan, Webb last of Nay Arch, Glen Cove,

Long Island, N.Y.

2 DIR, Iowa lost of Hydra Res, St Um of

Iowa, Iowa City, Iowa

I Dr. L. Landweber

1 DIR, St. Anthony Falls Hydra Lab, Univ of

Minnesota, Minneapolis, Minn.

1 DIR of Res, The Tech lust, Northwestern Univ,

Evanston, III.

1 Head, Dept NAME, MIT,

Cambridge 39, Mass.

I Editor, Bibliography of Tech Reports, Office of Tech Service, US Dept of Commerce, lashington 25, D.C.

1 SUPSHIPINSORD, Quincy 69, Vass.

3 Newport News Shipbldg 8. Dry Dock Co, Newport News, Va.

1 Asst Nay Arch

2 DIR. Hydra Lab

2 SUPSHIPINSORD, Nero York Shipbblg Corp,

Camden, N.J.

I Mr. J.I. Thompson, Nan Arch (Design)

31

Copies

I James Forrestal Res Ctr, Princeton Univ, Princeton, N.J.

Attn: Mr Maurice H. Smith, Asst to DIR

1 Tech Dir, Shoo Structural Corn, Nall Res

Council, Washington 25, D.C.

1 Dr. ILL Albertson, Head of Fluid Much Res,

Dent of Civil Etter, Colorado Cl Univ, Fort Collins, Colo.

Prof. IL A. Abkowitz, MIT, Cambridge 39, Mass.

1 fir. J.P. Breslin, ETT. SIT, 711 Hudson SL,

Hoboken, N.J.

1 Or. George C. Maiming, Prof Nov Arch, PHT, .;anturdge 39, Mass.

1 Prof. F.M. Lewis, Dept NAME, MIT,

Cambridge 39, Mass.

I Of. R.T. Knapp, Hydro Lab, CIT, Pasadena 4,

3 ALUSNA, London, bread

1 Dor, Nyder; Lab, Nan Res Council, Mama 2, Canada

I Or_ Georg Meridiem, Universitaet Hamburg, Berliner Tor 21, Germany

1 RADII R. Drard, Directeur, Bassin rEssais

Ses Carenes, 6 Boulevard Victor., Paris (15e). France

1 Be. L Italavard, Office National CEIndes

I de Recherches Ammo...drones, 25-39

Avenue re ia DIVISIOR - LeClerc, Chatillon

sons - Hamad (Seine) LC, Pais, France

1 Gen_ bag. U. Pugliese. Presidenza, Istituto

Nationale per Shull ed Experience di Architettma Narrate, Via delta Vasca lavale 89, Roma-Sete, Italy

1 Senor Manuel Lopez-Acevedo, Director,

Canal de Expemencias Hidrodonanicas, El Pardo, (Madrid) Carden de to Siena, Spain

1 Dr_ J. Dieudonne, Directed, Indite de Recherches

de la Constructioo finale, 47, roe de %aces

Paris (81, France

2 Dir, lederlandsh Scbeenshointlinedly Proefstation, Haagsteen 2, wageningen, the Netherlands

1 Ir. G. Vossers

1 Prof. J.K. Lunde, Statens Skipsmodeltanken, TybolL Trondheim, Norway

1 Or. Hans Edstrand, Dir, Statens Seepasmeelareantalt, Goteborg C. 14, Gilbraitaigatari, Sweden

1 Dir, British Shiplotilg Res Assoc, 5 Chesterfield Gardens, Curzon St, London Li, England

I Sail, Shop National Phy Lab, Teddington, Middlesex, England

1 Dr. J. °liaise. Res lost for ',apt Medi, Kyushu Univ, Hakozaki-Machi, Foknoka-shi, Japan

Calif.

Copies,

Chief Supt., Naval Res Estatlishomot

cis Fleet Vail Office, HaWax

NovaScotia, Canada

1 Prof. L.Howarth, Dept of Math, U otBristol

Bristol. Esgfaimf

It.L Gemilsma, Delft Shiphidg Lab, Prof. liekelmeg. Delft, The Netherlands

1, Dr. Siegfried Schuster, Neat, Bulls *del Basin

Versatchsaistalt for Nasser/lamodd &china.,

Schlessesissel in Tim :sites, Berlin 87, Gummy

3 Dr. M.N. Lerbs, Dir, Flaubert Model Basis, Ilambsrgische Schifltae-Versoctsaostalt,

LBramtelder Sic 164, Hamburg 33, Germany

IN!,, Admiralty Experiment Works, Gosport, Has,

Ersgiand

1 Dr.LC. Topper

1 Dr_11.G. Szebeliely, Genera; Electric Co,

3198ChestedSL Philaaelohia 4, Pa.

1 !Prof. CAL Proliaska, Ship Model Basic, Hjorteirersvel 99, Alampeshozy, Demi&

1 St.-Aldo Astieosi, lastitido de Peso's-sus Techocolocgicas, Cairo Postal 7141.

Sa Paulo,Brazil

3'4

1