A first look at some wave and wind data from trawlers

A Station of the

Department of Scientific and Industrial Research

Lab.

v.

Scheepshouwktrncle,

See note inside cover

Technische Hoescnoo!

SHIP REP. 46

e I.

_January1964

NATIONAL PHYSICAL

LABORATORY

SHIP DIVISION

A FIRST LOOK AT SOME WAVE AND WIND DATA FROM TRAWLERS

'by

Crown Copyright Reserved

The cource, muut be

acknoWlc4ge4-This report is a copy of a paper presented to a meeting of the

International Commission for the Northwest Atlantic Fisheries

held in Rome Injanuary 1964

Approved on behalf of Director, NPL

A FIRST LOOK .AT SOME WAVE AND WIND DATA FROM TRAWLERS

by

- J. A. Ewing and N. Hogben

CONTENIS

Introduction The Ana].ysis

I The Observations

ta processing

Choice of season and. area

4.. Tabular presentation of results

50 Graphicál presentation of results

6.

Study of the relations between wave he:Lght/Beaufort Number

and wave length/wave length calculated from wave period

Note on App].ications

Concluding remarks

Aciow1edgments References

INTRODUCTION

Seakindliness is particularly important for trawlers. Model tests in waves

can greatly help the designer to achieve good. seagoing qualities but they must be coupled with knowledge of the sea conditions both average and. extreme to be

encountered in service. At present, knowledge of conditions in the northern fishing grounds where distant water trawlers operate is vexy inadequate. A

scheme has therefore been organised (in collaboration with the White Fish

Authority and the Ministry of Agriculture, Fisheries and. Food) for collecting systematic sea data observations from selected. trawler skippers. Accounts of this scheme and the preliminary studies made to explore the reliability and the practical problems and techniques of observation have been given in the

refer-ènces

_(Hogben

and. Chaplin,

_1961;

Hogben,

_1962;

Hogben,

1963).

The present

paper takes a first look, at some of the observations which have meanwhile been

collected from the selected trawler skippers. The analysis carried out of the data so far available was intended mainly to test

analysis

procedure and to

examine, various forms of presentation and interpretation. It has. been thought

worth recording however because already the outline of a useful picture of sea

conditions is appearing.

ThE ANALYSIS The Observations

The trawler skippers who have kindly agreed tO cooperate in this research

'have been supplied with guidance notes. and. accessories such as stop watches to

help them in making the observations. The guidance, notes and procedure

recom-mended have been based on a study of the Marine Observer's Handbook and on the experience gained from the special visual observation trials (Hogben,

_1962).

The observations are recorded' on data sheets using a "ticking" principle for

ease of subsequent coding onto punched cards. A sample is shown (Fig. i) and

it will, be seen that there is space for 15 sets of observations on each sheet.

Data processing.

The punching of the cards is being carried out by the. Combines Tabulating

Installation of the Stationery Office and each set of observations is punched

on one card, the cards are being sorted using a machine in Mathematics Division, National Physical laboratory. At the time of writing (June, 1963) there are

about I ,.i 00 punched cards recording observations mainly from 1. trawlers.

Choice of seasonand area

Each card bears the date, time and. geographical position of observation

and for convenience the cards are sorted (following the practice of the

Meteorological Office) into months and, classified according to the Marsd.en system of numbered 10 degree squares of sea area. For this preliminary analysis it was decided

to

choose those cards for the months of Décémber, January and. February

and for the area shown in Fig. 2 wluch covers Marsden Squares 217, 218, 219, 251,

252, 285, 286 and.

_287.

The number of cards satisfying these conditions was found

to

be 331i; the subsequent sortiig operations were carried out using this group

of cards.

14.. Tabular presentation of results

Tables 1,

2, 3

and. l. show the distributions of wave height/Wave period, wave height/wave direction, wave direction/wave period. and. wind direction/ Beaufort Number respectively.

These four tables represent the basis for Yig.

2 and.

contain more

2

observations is less than 334.; this is because some entries on the data sheets

did not have an.observatiori.of one of the two variables, concerned.

Graphical presentation of results

In addition to tables of the results it is desirable to. have a picture of

wave and Win4 conditions occurring in various sea areas; Pig.. 2 has been con-.structed. with this in view.

The small graphs shown in Fig. 2 have been drawn using information given in Tables 1-4..

Graph (a) shows the 2-way cumulative frequency curves for Wave height and wave period together with three wave period/wave direction roses.

Graph (1,) gives information on the steepness of waves - the curves show the pro-bability of exceeding a given wave height when the wavelength is specified.

Graph (c) shows the Beaufort Nuntber/wind direction rose. Below the rose is a small table giving the frequency of occurrence of various Beaufort Numbers for aU wave directions.

In almost all case the wave and wind. directions given in each entry of the data sheets were found. o be the same. It was therefore not considered necessary to give roses of wave hight/wave direction corresponding to Table 2 since the

Beaufort Number/wind d2.rection rose was available in graph (c), and also there was found. to be good. corelition between wave height and Beaufort Number

(see Pig.

3).

'Study .of the relations between wave height/Beaufort Number and wave length/ wave, length calcuJAted from wave period

A separate study was carried out ta investigate the relationship between

wave height/Beaufort Nuiiber and wave length/wave length calculated from wave period. All the cards vailable. at, the time were used and. sorting operations

were carried. out. Tabls 5 and 6 show the results. .' .

-6.1 Wave .height/Beaufort Number

Prom Table 5 the mean wae height for each. Beaufort Number was calculated. and. the results plotted in Pig. 3. The number adjacent to 'each point in Fig. 3 gives, the number of observations at that Beaufort Number. A' curve 'has been

drawn through 'the point up to Beaufort 9.

This figure cou].d. be used to pred.iot the wave height in a given area if the

wind force is known. , .

6.2 Wave length/wave 'length calculated from, wave period

Table 6 was used to determine the mean wave period corresponding to each,. observed wave length. The wave length corresponding to the mean wave period was the calculated using the classical formula

2

= _where A - aye length wave period

Fig. 4. shows the graph of wave length calculated from mean wave period against

ratios Of

observed wave length 1 1 2

-

=

-,-and-wave length from mean -,-and-wave period ₃ 2 3

It is seen that all the points lie between the two lines K 1,13

_{an K}

2/3

and that at short wave lengths the points lie close to the line K = 1/3. This finding is in agreement with results shown in (Hogben,

_1962).

The value of K depends on the nature of the wave spectrum. When the spectrum contains only a narrow band of frequencies and is also long-crested then K is close to unity The theoretical value of K for a Neumann spectrum

(modified by a factor cos to give the angular dispersion of the waves) has

been given (Pierson,

195i)

as K =

2/3.

NOTE ON AP'[JGATIONS

An indication of the practical ajplications of data ofthis type has been

given (Hogben,

₁₉₆₁₎

but it may be useful to include here some further comments. Data about sea conditions in the fishing grounds are of interest from many

different points of view and no doubt will be of value to trawler operators as well as to designers. Here in Ship Division, NPL, they are to be used partly

as. information to be applied to miscellaneous design problems and to be available for consulting purposes. The most immediate and. clearcut application isto the

planning of wave generation..

In the tank in Ship Division, tests studying such features as speed loss,

motions and wetness can be conducted in regular or irregular waveS as occasion

demands and the irregular waves can be given any required spectral and.

statistical characteristics (Ewing,

_1962).

Thus for example it is possible to generate spectra which represent the sea likely to be generated by a given wind.

force (accorin tO a. Darbyshire

_(1961.)

or Neumann

₍₁₉₅₃

formulation). Spectra

can also be. set such that the estimates of mean height and period likely to be

made by an observer will have any chosen values. Hence it is possible to

generate wave spectra representing average or extreme conditions in a given area interms of observed wave and wind, data such as have been described.

CONCLUDING REMARKS

it would. be premature to draw any elaborate or firm conélusions from the

sample of data so far ana].ysed.. _{It is encouraging however to find already a} meaningful picture emerging in a form which has direct application to the

p].anning and interpretation of trawler tests

in

waves. It is also of interest to note results such as the relation of Beaufort Number and. wave height in Pig. 3 and the relation of wave length and. wave length calculated from Wave period in Fig. li which have a wider and. more fundamental sigzificance.

ACKNOIEDGMEIff

This paper is presented by permission of the Director of the National Physical laboratory and the Chairman of the White Fish Authority. Grateful

acknowledgment .is made for the cooperation of the

Mini

Mr of Agriculture,

Fisheries and Food, the Combined Tabulating Installation of the Stationery Office

and. Mathematics Division, NPL.

The authors wish to express particular appreciation to all members of the above organisations who contributed to this work and also to the trawler

sppers Captain W. March (Portia), Captain Wood (Arctic Vandal), Captain W. C. Hardie (Arsenal), Captain J. Cower (Cape Adair) and

Captain E. A. Binnington (Ernest Holt) for their patient efforts

in

collecting the data.

REI'ERENcES

D&RBYSHIRE,

I. 1961 - The

oxie. dirnensional

wave spectrum.

in the Atlantic Ocean

and. in coastal waters. Conference on

Ocean Wave Spectra,

Easton,

Marr1rtntl, USA.

EWING, J.

A.

1962. -

Th generation of

discrete wave spectra. in a ship tak.

Ship

Division Report

_35.

HOG.BEN, N. and. CHAPLIN, P. D. I %i A note on sea atate and 'seakeepin studies

on th research trawler Ernest Holt.

PAO Research Teasel

Forum,

ToIcyo.

HOGBEN,. N. I 961 -

Sea

state information and.

ship

design..

Marine

Observer,.

Fanuary

1961..

.

HOGBEN, N. 1962. Sea

state Observation studies on the s.s.

Cairnd.hu and.

r.v Ernest Holt.

Ship

Diviaion

Report 32.

HOGBEN, N. 1963

Sea tate

'stdies at the

Ship

Hydrodynamiàs. Laboratory, Fè].thm.

Marine

Observer, June 1963.

.. .'

NEUMAIIN,.

C. .1953 -

On ocean wave

spectra

and., a new method 'of.forecasting wind.

generated sea. Tech. Mein. 13. Beach Erosion Board..

PIERSON, V. J. 1951 - .An interpretation of the observable properties of taea' waves in terms of the energy

spectrum

of the Gaussian record. Thañsactions of the .Aierican Geophysical UEiion, vol.

35, no.5.'

TABLE I

WAVE PERIOD (sEc)

O-4. 5 6 ₇ 8 9

10

12

14.

Totals

o( O.00ni)

Ii

11

i( 0.3lni)

13 5 2 .2

22

3( c.91rn)

23

12.

9 7

2

53

5(1.52m)

7

10

6 4.

i8

8

7

60

7( 2.l3rn)

2 4. 4. 5 9

2

2 28

9( 2.74zn)

4. 3 6 4.

16

2

35.

ii( 335m)

1 6 _{3 9 3}

22

13( 3.96xn)

2

7

7

3

19

15( 4..57m)

1 2

5

Ii

3

1

23

17( 5.18m)

1 1

3

5

19(5.79m)

I

2

5

1 ₉

21( 6.4.Oxn)

2

2

1.

5

23(7.Olm)

1 ₃ 1

5

25( 7.62m)

1 2 3 6

27( 8.23ni.)

1 4. 1 6

29(8.84m)

2

2.

31( 9.4.5m.)

I I

3.3(10.06m)

2 . 2

3(1O.67m)

. 2

7

9

37(11.28w)

1 2

3

.39(11.89m)

. 2 4.

4.0(12.19m)

I

2 3

4.5(13.72m)

. . . I I TOTALS 54.

29

25 22 4.7 4.9

69

31 8 334.

TABLE 2

WAVE DIREcTION (nEc.)

000 00 060

090 120 150 180

210

24.0

270

0O'

330 Totals

o( o.00)'

. 2

1(O.3Ini)

1 2 2 5 2 2 1 1 2, 3 21

3(0.91m)3 97

8

3

'23

2 1

25 6.51.

( 1.52w)

1

10

15

3 2

.3

2 1 ₃ li. 4.

10

58

'7(2.13m) 336.2

1

53

2 1

2

28

9( 2.74)

'2 2 7 - 1 1 6 4.

7

3

35

il( 3.35rn)

3 1

₇

6 1 1 3

22

13( 3.96m)

2 1

2

1 . 1 2

.5

19

j5(4..57in)

2 4.

'1

1 1 5 2 1 6 23

ii( 5.18m)

.. '

I

I ' 3 . 5

19( 5.7n).

1 '

1.

1 1 . i ' 2 2 .

21 ('6.4.0w)

i

. . 1 1.

5

23(7.01w)

1 1

2

1 5

25(7.62w)

1 1 1

3

6

27( 8.23w)

.29(8.84w)

' . I' 1

'1

. . '., I .

I

I I 1 ₅

.2

'31(' 9.4.5w)

' , . . .

I

'1

33(I0.O6rn)

I

. .. '

i

. ..

2'.

.35(10.67w)

1 1 1 1 1

2

1 1 9

37(11,a?8m)

. . . ' . I ' ' .

2

3

39(11089m)

2

2

4.

4.0(12.19w)

2 1

3

(I3.72m).

i

. '

.'

' '

''

. . TcYA.LS

25

29

8

11

15

20

28

26

31 4.3

326

H

7

TABLE 3 'WAVE PERIOD (sEc)

0-4.5

6 ₇ 8

91O:12.

11k.

Totals

000 12 1 1 1 2

6

2 ₂₅

.030

10

8

2*2

i3

_{2 35} 060 6

'3

2 _{5 16 8 12 3 55} 090

8'

2 2 2 5 3 6 1 29 120. 5 1 2 . 8 150 1 3 2 1 2 1 11' 180 2 1 1 ₅ 2 1. ₁₅ 210 .1 2 2 2 ₅ 2 2 . 20 24.0 1 1 _.3

6 12.

₂₈ 270 ₃ , 2 1 1 6 _{3 4. 3} ' 3 26 300 .3 2 1

'3

8 _{.3 6}

₅

₃₁

330'

2 _{3 5}

23 11

_{12 4. 1 4.3} TCYPAT.R

52'

27 _{21 22 4.7 4.9 69 31} ' 8 326

TABLE 4. BEAUPORT NUMBER 0 1 2 3 4. 5 6 7 8 9 10

TotaiB

000

.7.:

1 4. 3 2 3

i

21 030

11

7 9 6 6 2 1 ₃ 2 1 39 060 1 1 5 20

ii

5 7 3 090 2 2 7 5 4. 1 2 4. 1 28 120 3 3 3 2 11

.150.

2 2 1 2 2 1 1

11.

180 1

.1

2 3. 2 2 3 :2 16 210 4. 1

23 3.3

3 2 1 22 24.0

4.73.1

2 17 270 3 1 2 2 8 3 2 7 4. 32 300 1 2 2 6 8 2 7 2 30 330 8 8 12 8 3 3 1 4.3 T0TAL 8 9 24.

4.164.

66 33 35 31 10 2 323

9 TABLE 5 BE&UPORT NUMBER 0 1 2 -

3

4.

5

6 7'

8

9

10

11

12

To1s

o( 0.00n)

33 27 16 2 2 2 2

8l.

j( 0.3lin)

18

3.5 26

16

1 1 1 98

3( 0,91m)

2 4.0 ₈₉

38

9 1 1

180

5( i.52in)

I

2

14. 41 75 18 6

2

2 161

7( 2.l3zn)

2

8

4.0 26 9 6 ₃ 94.

9( 2.74iii)

I 4. 29 4.2 14. 3 6 ₉₉

11( 3.35n)

13( 3.96m)

3

8

35

26 13

1l.

10

8

5

6 74. 54.

15( 4..57ni)

1 .3 18 24. 21

18

2 ₈₇

17( 5.i8ni)

1 1

18

1 6 27

.19( 5.79m)

21(6.4.Oni)

,

10

7 3 3 6

7

3 3 22

20

23(7.Ojni)

2 6 1 9

25( 7.62in)

2

₁₅

2

19

27( 8.23m)

12

1 ₁₃

29(8.84nt)

4.

2

6

31( 9.4.5ni)

1 1

2

33(10.06m)

2

2

4.

35(10.67in)

9 2

ii

37(11.28ni)

5 5

39(11.89m)

5

1 6

4.0(12.19m)

4.2(12.80m)

, 3 I

3

I

4.5(13.72ia)

50(15.24m)

, I 2 1 I 3

5.5(16.76m)

1 1 2 'TOTALS 34.

50 109 176

208

177

121 1C1

82

19

6 1 1 1085 Mean wave

heiht(ft)

0 1.0

2.4.

3.8

5.5

9.5

13.6

17.8

19.3

29,4. 4.6.8

50

55 Mean wave

height(m)

0.00 0.31 0.73 1.16 1.68 2.90

4..15

5.l.3

5.88

8.96 14..96 15.24-16.76

10

PA1Th1l! 6

WAVE PERIOD (aEc)

9

10

12

14.

Totals

Mèan Pé±iód.

50( 15.2m)

200

16 7 1i I 5

280

-.

75( 22.9m)

2

42

21 6 9 6 6 93

6.

ioo( 30.5in)

3

8

32

22 23

7

5

.2

102

7.0

125(

8.frn)

3

20 17 26 25 22 LI.

117

8.2

150( 4.5.7in)

I 2 5 24. 28 13 4.6

10

131

8.8

175( 53.3m)

I 3 13 I 6

5

14. 14. 8

96

2oo( 61.Om)

5 27 14. 29 11 4. 90 .

9.5

225( 68.6n)

I 15 8 11 8 4.5

9.6

250( 76.2ni)

I

7

18

10

11 I

48

9.8

275( 83.8m)

2.

t7

13 3 35

9.6;

300( 91 .4m)

5 13 11

29

10.6

.325( 99.lni)

2 5

7

14.

10.9

350(1O6.7n)

2 LI.

10

.

12,4.

4.00(121 .9in) I

2

2

5

12.4.

500(152.4in)

I I

14.0

TLLS

206

.103

97 96

157

I 21

182

87

1074.

eo 70 60 50 40 30 20 10 0 '0 20 30 40 50 eo 70 eo so

60

50

40

WAVE AND WIND CONDITIONS

DEC. JAN, FEB.

so 40 A R E A I00 90 80 70 60 0I_l0 4° 30 20 I0 0 40 .3O )20 lD ALL. (a) Sec l0 272 08SRVA?IOIJ5/

WAVE HEIH?(feet) HEIG)171 WAVE LD4GH FROM OBSERVED PERIOD (A) ROSE 323 OBSERVATIONS

0

-s

20

i5'2°i4' i2Ii'3i

kEY{c

0-I 2-34467*8 (b) (c)

FIG. 2

Ii1

iII

288 - 264

lU

2.. 213 ₂₁₂ 211 208

Is'

172 I -I

I

--334OERVATI0N5 .R05( ShALC I

I

I-I ddIbIJjO 'sec 41

60

50

0

2

4

6

9

BEAUFOR'T NUMBER

oo0

800

Id

0

z600

Li

200

10

0

100

₂₀₀

₃₀₀

₄₀₀

₅₀₀

OBSERVED WAVE LENGTH

r)