Dynamic waterline seakeeping predictions for a fishing vessel

(1)

_ AUG. 1978

ARCHEF

DAVID W. TAYLOR NAVAL SHIP

RESEARCH AND DEVELOPMENT CENTER

Bethesda, Md. 20084

DYNAMIC WATERLINE SEAKEEPING PREDICTIONS FOR A FISHING VESSEL

by R. M. Watkins and N. K. Bales

Lab. y. Scheepsbouwkunde

Technische Hogcschß

APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED

SHIP PERFORMANCE DEPARTMENT

May 1976

SPD64302

(2)

MAJOR DTNSRDC ORGANIZATIONAL COMPONENTS

OF FICE RIN CHA AGE

CAR DE R OCK 05 STRUCTURES DEPARTMENT 17 SHIP ACOUSTICS DEPARTMENT 19 MATERIALS DEPARTMENT 28 DT NS R DC COMMANDER 00 TECHNICAL DIRECTOR 01

OFF ICE R. INCH ARG E

ANNAPOLIS 04 AVIATION AND SURFACE EFFECTS DEPARTMENT COMPUTATION AND MATHEMATICS DEPARTMENT 18 PROPULSION AND AUXILIARY SYSTEMS DEPARTMENT ₂₇ CENTRAL INST R U M E N T AllO N DEPARTMENT 29 SYSTEMS DEVELOPMENT DEPARTMENT 11 SHIP PERFORMANCE DEPARTMENT 15

(3)

UNCLASSIFIED

SEC»'TY CLASSIFICATION OF TI4IS PAGE (Wh.n Oat. nt.r.d)

D D t FORMJAN 73 1473 EDITION OF I NOV65 IS OBSOLETES

S/N 0102-014-6601 UNCLASS I FI ED

SECURITY CLASSIFICATION OF THIS PAGE (*..n Data Sniarad)

nEP,T

ChIuEITIr

PAIE

T '.)T LJ'.J U 1 I I _{BEFORE COMPLETING FORM}READ INSTRUCTIONS

¶ REPORT NUMBER

SPD-643-02

2. GOVT ACCESSION NO. 3 RECIPIENTS CATALOG NUMBER

4 TITLE (and SubtItle)

DYNAMIC WATERLINE SEAKEEPING PREDICTIONS FOR A

FI SII ING VESSEL

5 TYPE OF REPORT & PERIOD COVERED

Final

6. PERFORMING ORG. REPORT NUMeER

7. AUTHOR(s)

R. M. Watkins and N. K. Bales

5. CONTRACT OP GRANT NUMBER(S)

PERFORMING ORGANIZATION NAME AND ADDRESS Ship Performance Department

David W. Taylor Naval Ship R&D Center

Bethesda, Maryland 20084

IO PROGRAM ELEMENT.PROJECT. TASK AREA A WORK UNIT NUMBERS

Work Unit No.

l-1568-014

IL CONTROLLING OFFICE NAME ANO ADDRESS

United States Coast Guard

400 Seventh Street, S.W. Washington, D.C. 20590 ¶2 REPORT DATE May ₁₉₇₆ 3. NUMBEROF PAGES 17

14 MONITORING AGENCY NAME & AOORESS(II different from Controlling OffIce) 15 SECURITY CLASS. (of title report)

Unclassified

ISa. DECLASSI FICATION DOWNGRADING SCHEDULE

6 DISTRIBUTION STATEMENT (of title Report)

APPROVED FOR PUBLIC RELEASE: DISTRIBUTION UNLIMITED

¶7. DISTRIBUTION STATEMENT (of the ab.lracl entered In Block 20 if different 1,0v,, Report)

15. SUPPLEMENTARY NOTES

19 KEY WORDS (Continue or, reverie eid. if nec..ury td identify by block number)

Seakeeping, Fishing Boats, Dynamic Waterline

20. ABSTRACT (Continue on reverie aide if nececeary .d identify by block number)

This report examines the use of a dynamic waterline for strip theory motion computations for a full-huH fishing vessel. This vessel exhibited considerable trim, sinkage, and bow wave at high speed. Because of this, it

was thought that the use of an experimentally determined high speed waterline could improve prediction accuracy. It is shown, however, that no improvement

was obtained. It was concluded that computational errors introduced by the

dynamic waterline were negligible compared to errors introduced by the full-hulled vessel's violation of strip theory assumDtions.

(4)

(5)

TABLE OF CONTENTS Page ABSTRACT t t t t t I I t I t t g g t t t _t s g Q ç ADMINISTRATIVE INFORMATION * t . . I NTRODUCTION , . t i

PROCEDUREANDRESULTS

'tg

gt

t o 2 CONCLUSIONS

o...tt,g,..ggg....00ggggg

₃ REFERENCES

ggg.ggg,

gg..

t t t t t t g t g LIST OF FIGURES

Figure 1 Body Plan of Vessel Investigated o g g g g o o g 5

Figure 2 Calm Water Trim, Sinkage and Wave Profile at 15 Knots . 6

Figure ₃ Pitch at 15 Knots g g g g o g . o g g g g g g o 7

Figure Heave at 15 Knots g

g gggggoggg g

g 8

Figure 5 Pitch-to-Wave arid Heave-to-Wave Phases at ₁₅ Knots ₉ Figure 6 Station 0.0 Relative Motion at 15 Knots o o 10

Figure 7 Station lO Relative Motion at

_{15 Knots}

o t g g g

li

Figure 8 Station _2g5 Relative Motion at 15 Knots . g t g g g g o g 12

Figure ₉ Longtudina1 Center of Buoyancy Relative Motion

(6)

NOTAT ION

Single amplitude of pitch ¡n degrees

VM Maximum wave slope In degrees Wavelength In metres

ZA Single amplitude of heave ¡n metres Single amplitude of wave in metres

L Ship length between perpendiculars ¡n metres

Pitch-to-wave phase angle In degrees Heave-to-wave phase angle in degrees

rA Single amplitude of ship-to-wave relative motion in metres

(7)

ABSTRACT

This report examines the use of a dynamic waterline for strip theory

motion computations for a full-hull fishing vessel. This vessel exhibited considerable trim, sinkage, and bow wave at high speed, Because of this, it

was thought that the use of an experimentally determined high speed waterline

could improve prediction accuracy. It is shown, however, that no improvement was obtained. It was concluded that computational errors introduced by the

dynamic waterline were negligible compared toerrors Introduced by the

full-hulled vessel's violation of strip theory assumptions.

ADMINISTRATIVE INFORMATION

The work reported herein was sponsored by the United States Coast Guard

(USCG). Amendment No. 2 to Military Interdepartmental Purchase Request

Z70099-5-50646

was the funding document. At the David W. Taylor Naval Ship Research and Development Center (DTNSRDC) the work was identified by Work Unit

Number

l-1568-014.

INTRODUCTION

In November of 1975, DTNSRDC released the report "Validity of a Strip

Theory-Linear Superposition Approach to Predicting Probabilities of Deck

Wetness for a Fishing Vessel," Reference 1. This report concluded that strip theory was not generally applicable because of the incompatibility of the

vessel's full hull form (see FIgure 1) with state-of-the-art theory. However, it was suggested in the report that computations performed for the fishing

vessel using the experimentally determined 15-knot waterline might improve

predictions at 15 knots. This suggestion was based on the observation of a

large bow wave, and trim and sinkage at high speeds, These phenomena caused a considerable change ¡n the underwater body from that at zero knots, The

(8)

!n the interest of ¡rnproving prediction techniques, the USCG sponsored

an investigation into the effects of using a 'dynamic' waterline for strip

theory computations. The investigation was conducted at DTNSRDC This

docu-ment describes the revised computations and the results thereof.

PROCEDURE AND RESULTS

All revised computations were made using the Frank Close-Fit Ship-Motion

Computer Program (YF 17, see Reference 2) so that they would be directly compa-rable to the original computations in Reference 1.

Data from the Reference I experiment defined the trim, sinkage, and bow

wave of the fishing vessel at 15 knots. These data are illustrated by Figure

2.

Two YF 17 computations with variations of waterline were made in an

attempt to improve predictions of ship behavior, The first computation was made using the waterline resulting from experimentally measured values of trim

and sinkage

_(3.5

degrees bow up and 0.1457 metres (1.5 feet) down, respectively). This waterline is identified in Figure 2 as revised waterline #1.

The results of the first computation were discouraging The quality of

the predictions was less than that of the original computations for the static

waterline. It can be seen in Figures

3,

14, and 6 through 9 that the predicted response magnitudes increased, and that an additional error ¡n predicting peak

frequencies was introduced. Pitch and heave phase angle predictions also

degenerated as shown in Figure 5.

The computation for revised waterline #1 gave rise to an anomaly in ship

hydrostatics. The displacement of the hull at this waterline was found to be 18 percent greater than the displacement reported in Reference I for the static

waterline (1+61 versus 390 tonnes). Such a change in displacement was difficult to justify in the context of speed-related lift force.

an attempt to resolve this anomaly, a second computation was performed

using the vessel's wave profile (from measurements in calm water at 15 knots)

as a waterline. Figure 1 identifies this waterline as revised waterline #2.

(9)

A displacement of 42l tonnes, representing an 8 percent increase with respect

to the static case, was computed for revised waterline #2,

Response computations for revised waterline #2 produced results which

were, for practical purposes, identical to those reported in Reference 1 for

the static waterline. The comparison Is shown by Figures 3 through 9. With respect to Figure 9, ¡t should be noted that the longitudinal center of

buoyan-cy was located at Station 5.2 for the static waterline, at Station 5.6 for

revised waterline #1, and at Station 5.1 for revised waterline #2. The

measurements shown apply to the static waterline longitudinal center of

buoyancy.

CONCLUSIONS

Neither of the two revised waterlines used resulted in the hoped-for

improvement ¡n prediction quality. It can be said, therefore, that the dynamc waterline had a negligible ¡nfluence on prediction capabilities when compared

to other basic strip theory assumptions that were violated. Current strip theory assumes a slender hull form with its subsequent small effect on

en-countered wave patterns and slow rate of change of hydrodynamic phenomena ¡n

the longitudinal direction. The fishing vessel with a length to beam ratio of

33, high draft, and high Fraude number operating range must consequently

await state-of-the-art advances ¡n theory before its performance in a seaway

can be accurately predicted without recourse to experiments.

(10)

REFERENCES

1. Bales, NK. et al., tiValidity of a Strip TheoryLinear Superpostíon

Approach to Pred1ctng Probabflities of Deck Wetness for a Fîshng

Vessel,tt DTNSRDC Report SPD-643-Ol, November 1975e

2 Frank, W, and N. Salvesen, uThe Frank Close-Fit Ship-Motion Computer

Program,' NSRDC Report

3289,

June _1970.

(11)

SHEER ST4 2.5 FO'C'S'LE DECK

(183M) (0.91M)

(0.91M) (1.83M)

Figure 1 - Body Plan of Vessel Investigated

EER & BULWARK TOP IN DECK PER KNUCKEL WER KNUCKEL 14' (4.27 M) 12' (3.66 M) -10' (3.05 M) 8' (2.44 M) BL

BULWARKTOP

POOP DECK MAIN DECK

MI Up

tt

10 6

VA1I

4TION SPACING METERS

r

CHINE 6' 3' Q 3' 6'

(12)

ZERO SPEED WATERLINE

REVISED WATERLINE #1 (INCORPORATES TRIM AND

SIN KAG E)

REVISED WATERLINE 2 (INCORPORATES TRIM, SINKAGE AND WAVE PROFILE)

NOTE: VERTICAL SCALE EXAGGERATED

Figure 2 - Cairn Water Trim Sinkage and Wave Profile

at 15 Knots

(13)

4.

3.0 - 2.0

VM 1.0

0.0

7

¡

II

]

15 KNOTS

i

\

'III

1.1 /

(FROM REFERENCE 1) STRIP THEORY REVISED WATERLINE #1 (YF-17) REVISED WATERLINE COMPUTATIONS 3 EXPERIMENT (FROM REFERENCE 1)

0.0

1.0

20

30

4.0

X/L

Figure 3 - Pitch at 15 Knots

- - a

(14)

4.0

3.0

ZA

;

2.0

SA 1.0

0.0

1 _{STRIP THEORY} (FROM REFERENCE 1) (Y F-17) REVISED WATERLINE #1 REVISED WATERLINE #2

\

COMPUTATIONS T EXPERIMENT

j

_s J (FROMREFERENCE1) 8

15 KNOTS

I

/ 124\\\

.

_I

0.0

1.0

20 ₃₀

_4.0

AlL

(15)

+ loo

- loo

+40

60

160

260

ZERO SPEED WATERLINE (FROM REFERENCE 1) REVISED WATERLINE #1 REVISED WATERLINE #2 EXPERIMENT J (FROM REFERENCE 1) 9 STRIP THEORY (Y F-17) COMPUTATIONS X/L

Figure 5 - Pitch-to-Wave and Heave-to-Wave Phases at 15 Knots

'/'15KNOTS

-

-J

o

\

I >

-T

15 KNOTS

05

1.0

15

20

25

3.0

₃₅

XI L

05

10

15

20

25

30

35

Eo o

(16)

-rA

n

6.0

5.0

4.0

30

2.0

1.0

0.0

ZERO SPEED WATERLINE (FROM REFERENCE 1) REVISED WATERLINE #1 REVISED WATERLINE #2 EXPERIMENT (FROM REFERENCE 1)

1.0

STRIP THEORY

(VF-li)

COMPUTATIONS

2.0

X/L

Figure 6 - Station 0.0 Relative Motion at 15 Knots

lo

30

O VECTOR SUM OF

MEASURED PITCH

HEAVE AND WAVE

(FROM REFERENCE 1)

40 I

I

15 KNOTS

STA.0

I

I?

o

\

-o

--\

\\

o

O

(17)

6.0

5.0

4.0

rA

-

3.0

2.0

1.0

0.0

ZERO SPEED WATERLINE (FROM REFERENCE 1) REVISED WATERLINE #1 REVISED WATERLINE #2 EXPERIMENT (FROM REFERENCE 1) STRIP THEORY (Y F-17) COMPUTAT IONS 11

Q

VECTOR SUM OF MEASURED PITCH HEAVE AND WAVE (FROM REFERENCE 1)

-I

15 KNOTS

STA.1

I

I_.

I

4:

\

T

Io_

o

-

\\

L

N

OQ

00

10

20

30

4.0

XI L

Figure 7 - Station 1.0 Relative Motion at 15 Knots

ea

(18)

n

5.0

4.0

rA

-

3.0

2.0

1.0

0.

ZERO SPEED WATERLINE (FROM REFERENCE 1) REVISED WATERLINE #1 REVISED WATERLINE #2 E XPE R IME NT IFROM REFERENCE 1)

I

STRIP THEORY (Y F-17) COMPUTAT IONS 12

Q

VECTOR SUM OF MEAS'JRED PITCH

HEAVE AND WAVE

(FROM REFERENCE 1)

15 KNOTS

STA 2.5

¡

/

s

/

s

.1

\

0.0

10

2.0

30

4.0

X/L

(19)

¡1

6.0

5.0

4.0 - 3.0

2.0

1.0

0.0

ZERO SPEED WATERLINE ]

(FROM REFERENCE 1) I STRIP THEORY REVISED WATERLINE #1 (YF-17) REVISED WATERLINE COMPUTATIONS EXPERIMENT