Studies of the behaviour of fishing boats from the viewpoint of seakeeping qualities by means of field measurements

Technische I-Iogeschool

Delfi

Studies of the Behaviour of Fishing Boats from the Viewpoint

of Seakeeping Qualities by Means of Field Measurements

Rihei Kawashima* and Hideyuki Nishinokubi**

*The Faculty of Fisheries, Hokkaido University

Minato-cho, Hakodate, 041, Japan **The Faculty of Fisheries, iVagasaki University

Bunkyo-cho, Nagasaki, 852, Japan

Abstract

These are studies on the seakeeping qualities of fishing boats during fishing operations. Using a specially devised wave measuring apparatus, the encountered wave heights and the motions of fishing boats were measured on board commercial fishing boats during fishing operations. The methods of the statistical analysis of stochastic processes were applied to

these obtained data, and several statistical properties were derived. Based on the results, the numerical forecasting of the motions of fishing boats were discussed.

Introduction

Concerning the studies of ship maneuvertng in rough seas, there have been attempts to deduce a theory of ship motions in random seas, as a scientific method to replace the traditional empirical method, since on early stage of the society.(1)(2)(3)

The study of seakeeping qualities has progressed for recent years, and has been accompanied by a like progress in the study of ocean waves.(4) Presently, these studies may be considered to form part of the theoretical background of seamanship.

With this viewpoint in mind, the studies of the seakeeping qualities of fishing boats were performed by making field measurements during fishing operations. There are several fundamental methods for

these studies, one of them is a theoretical method, done by solving the equations of the motions with 6-degrees of freedom, another is the study of ship behaviours at sea, based on the analysis of a time series regarding the ship motions to be a stationary stochastic process.

Concerning fishing boats, it is necessary to clarify the characteristics of their behaviours on ocean waves not only for ship stability safety but also for safety during fishing operations at sea.

Speaking of the peculiarities of fishing boats, there is a broad range of variations in the conditions they encounter during fishing operations, their motions are restricted by their fishing gear during fishing operations, and their motions due to ocean waves are larger than those of other types of ships (i.e., a general cargo ship) in similar seaway situations.

Based on the measurements of the behaviours of fishing boats ac sea, a scientific method is needed to give a rational understanding of these behaviours through statistical analysis, with the help of decisive methods.

In these studies, experiments were carried out aboard commercial rhing boats - bull trawlers - in the East China Sea.

Experiment and analysis

In this section, only the special features of the experiments will be briefly described, as follows: 2.1 The bull trawlerandthe waves on the East China Sea

-.

37-i t n 'e e [e ie

i,

'n. lt

i)

In 8

The bull trawler

There are several kinds of bull trawlers, their tonnages range from 50 GT to 500 GT. These bull rs operate throughout the year on the East China Sea. For the typical types of bull trawlers used se experiments (with wave measuring apparatus on board) the principal dimensions and body lines given in Table i and Fig. 1, respectively.

ab1e 1. Principal dimensions and conditions of bull trawlers

Light : Light condition, F.L.P. Full load condition F.F.L. r Full load arrival condition

F.L:A. : Full load leaving port condition E.H.A. : Empty load arrival condition

3.0 2.0 1.0 1.02.030 B.LB.LB.L B.LB.LBJ.

2.12 The wave

As to the China Sea, the wave heights ari abscissa indicat an ordinate indi the zero-cross r waves and aut wave heights in autumn, and th greater than thai

These exp season, except cruises ranged fr cruise, the mea made during con

2.2 Measu reme

To measun boats and ocean wave measuring relative encounte

In this stuc were measured, t relative wave hei were measured dt of double integra method for this p The double values, was carrie frequency ranges than 15 deg..

The error o: the range of frequ

-38-Fishing

Boa t Lrg B D Lpp GT Disp. Draft GM Trim Cb Fb Tr Kr

4-Maru 29.60 6.30 2.80 29.30 114.29 700 205.240 1.983 0.900 1.915 0.630 1.140 7.38 3.528 )-Maru 31.00 6.70 2.85 30.60 134.72 780 223.513 1.890 1.207 2.180 0.634 1.231 6.91 3.779 7T-Maru 34.00 7.30 3.40 33.60 193.14 700 277.490 2.028 0.710 2.684 0.582 1.602 7.49 3.140 3T-Maru 34.00 7.30 3.40 33.60 193.94 1000 276.650 2.020 0.800 2.745 0.582 1.610 7.44 3.310 IT-Maru 34.00 7.30 3.40 33.60 194.02 1000 279.880 2.045 0.890 2.873 0.583 1.578 7.33 3.430 7T-Maru 32.20 7.00 3.35 31.80 197.12 650 254.960 2.053 0.670 2.510 0.565 1.544 7.67 3.050

-uuIIUIVPii

lWtJJ. 4.00 V.1.. 4.00W J. 3.00 W.L _A?1J 3.00W.L 2.00W.L vra 2.00 V.L 0 1 2 3 4 5M 1.00 WI. 1.00 Wi. Bi. -'- BASELINE N 5.00 Vi. 4.00 Wi. 3.00 W.L 2.00 Wi.. 1.00 Wi.

23

Methods of In these ex ed and recorded. 2.3.1 The statistic There are t processing of max The former motion and wave for the long-term of the motionsan 232 Spectrum an The power s Obtained by Blac between waves an i. i.

I.

b -LINE

.-1 BASE UNE

-

:

-A

.--=-

z_&_

3.00 BI. L 2. Bi. ER LINE ...-. - 1.00 Bi. cENTER LINE

2.12 The waves on the East China Sea

As to the properties of the waves in the East China Sea, the relation between wave periods and wave heights are shown in Fig. 2. In the figure, an abscissa indicates the significant wave heights, and an ordinate indicates the wave periods obtained by

the zero-crossing method. In comparing winter

waves and autumn waves, it was found that the wave heights in winter were higher than those in

autumn, and that the wave steepness in winter was greater than that in autumn.

These experiments were performed for each

season, except spring, and the duration of the

cruises ranged from 35 days to 45 days. For each

cruise, the measurements of wave heights were

made during commercial fishing operations.

-

39-sec.

lo-u, U) o b

o

o o' o. Q, WINTER (19Th. 1.17 - 2.28) AUTIJN (1973.10.22 - U.15) o

° :.1

O

, Oo°o

f:

_o 0° I

ø*

S o o o 0 1 2 3 1. 5 6m Wave H.(113 max.)

Fig. 2. Wave properties of the EastChina Sea

23 Methods of statistical analysis of observed data(6)(7)(8)

In these experiments, the wave heights, and the rolling, pitching and heaving motions were measur-ed and recordmeasur-ed. Statistical analyses were applimeasur-ed to these data.

2.3.1 The statistical properties of wave heights and the ship's motions

There are two ways to analyse these data to irnd their distribution function, one is by the statistical processing of maxima as a random function, the other is by the u,se of order statistics.

The former was used for the short-term data analysis, by which the maxima distribution for each

motion and wave height could be obtained from the data recorded for every cruise. The latter was used

for the long-term data analysis, by which the distribution functions were obtained for the r.m.s. values

of the motions and wave heights of every cruise.

232 Spectrum analysis

The power spectra of the observed records of the motions of fishing boats and wave heights were

obtained by Blackman-Tukey's method, with Akaike's smoothing coefficients. Concerning the relation

between waves and the motions of fishing boats, the frequency response functions were calculated, with

22 Measurement of wave heights(5)

To measure the encountered wave heights and to obtain the relation between the motion of fishing boats and ocean wave form, simultaneously, during the cruising course, the authors devised a step-type wave measuring apparatus that could be mounted on a midship side of a fishing boat, and that could the relative encountered wave heights vertical to the sea surface at a given point on the ship's body.

In this study, as the relative wave heights, which included the components of the ship's motions,

were measured, the encountered wave heights were obtained by substracting the ship's motions from the relative wave heights algebraically. For this calculation, as the pitching angles and heaving accelerations were measured during the ship's motions, the accelerations must be converted into displacements by way

of double integration, on the basis of the recorded motions. The authors obtained a practical, effective

method for this putpose. The following results were obtained by this method.

The double integration of the observed vertical accelerations, which were recorded as analogous values, was carried by the approximate integral method by the use of an active band pass filter with

frequency ranges from 0.03 Hz to 0.07 Hz. The amplitude gain was ± 0.5 dB, and the phase shift was less than 15 deg..

The error of measurements of the wave heights by this method was estimated to be within 10% of the range of frequency for the heaving motions of the fishing boat by experimental way.

wave heights as input forces and the motions of fishing boats as output forces, by using the cross tra analyses method proposed by Akaike and the others.(8)

eakeeping qualities of the fishing boats

In these experiments, the 104 wave and fishing boat motion measurement periods were performed ing 42 days of winter cruising on board the above mentioned bull trawler.

Statistical properties of the wave heights and the ship's motions .1 Maxima distributions of wave heights and ship motions

One maxima distribution is shown in Fig. 3 and one of the accumulated distributions is shown in

.4.

Wave N=79 a=1.79 15 10 >, u C w Roll

N55

a=8.74 98 97 96 94 92 90 P(r)-2Ç-exp( r2 80 70 60 40 20 0 1 2

Fig. 4. Cumulated frequency distributions of maxima

-

40-04 8 12162D14 2ß326 440-044

r(m)

Fig. 3.Frequency distribution of maxima of the motions of fishing boats (a), (b)

99

of

ve o ₃ .6 .9 12 15 18 21 2.4 r(deg.) The narrow fre power Spec to be narrc distributior relations w These according t the theoret shown in T Table 2 A l/3ri I/IO ir 3.1.2 Relatjc motion A regr relation of t significant va and the linea The regressia fishing boat the boat are t Based on thi the motions obvious.

Concern the most elfe fishing operati

were the sm

quartering and when the wave trawling Cours for fishing o

conditions thi

Though the e Commercial fisi most severe sea 3.1.3 Long-terri heights an

According

The statistical distribution of data is difficult to determine in general, but when theprocess has a narrow frequency spectrum, the data are distributed according to the Rayleigh distribution. As the power spectra of the motions of fishing boats and wave heights will be shown later (their spectra proved to be narrow), the theoretical distribution functions are indicated by solid lines in Fig. 3 and Fig. 4. The distributions of the observed data were considered to be coincident with those of the theoretical their relations were also affirmed by X2 tests.

These results showed that the maxima of the motions during fishing operations were distributed according to Rayleigh distributions. For these statistics, the ratio between each average of maxima and the theoretical standard deviations that were calculated by the Gaussian distribution, respectively, are -shown in Table 2.

Table 2 Estimation coefficients of maxima

3.1.2 Relations between wave heights and the

motions of fishing boats

A regression analysis was made for each relation of the significant wave heights and the significant values of the motions of fishing boats, and the linear regression equations were obtained. The regression coefficients for each motion of a fishing boat for the encountered wave angle and the boat are shown in Fig. 5 by polar coordinate. Based on this figure, the statistical properties of the motions of fishing boats in a seaway were obvious.

Concerning the rolling motions which were the most effective for working efficiency during fishing operations: as shown in Fig. 5, the motions

were the smallest for head sea, and large for

quartering and following seas. Practically speaking, when the wave heights grew to above 4 meters. the trawling course selected would always be head sea for fishing operations furthermore, in severe conditions the operation would be stopped. Though the experiments were performed aboard commercial fishing boats, it was reported that the most severe sea state was observed in head seas.

3.1.3

Long.term maxima distribution of wave

heights and the motions of fishing boats According to order statistics, the root mean squares of maxima on the record of each cruise

Fig. 5. Regressive coefficient between wave heights and ship's motions versus encountered angles between ship andwave

999 990 900 70 50 30 20 IO 5 3 2 .3 .4 5 2 I X O Wove(m) Reti. (deg.) Pitch ( -Heo'e( m)

R.(.)

3 ; 5 791) 1520 30 X

Fig. 6 Probability distributions on Weibul probability paper

41-Wave H. Pitch . Roll Heave R. Wave H.

Average (1.25) 1.18 1.20 1.23 1.21 1.15

1/3 max. ave. (2.00) 1.81 1.82 1.89 1.86 1.77

1/lo max. a've. (2.55) 2.25 2.30 2.35 2.30 2.22

re dealt for statistical analyses. The results obtained were that the distributions of wave heights and aving motions fitted well with the logarithmic-normal distribution functions, and that the rolling and ching motions fitted well with the Weibul distribution functions. For these results, the accumulated ribul distribution paper was used for their expressions. See Fig. 6. According to the accumulated ribul distribution functions, these results were affirmed by the test. Their parameters are indicated Table 3.

Table 3. Parameters for Weibul distributions

(X -r)m f(x) = --(x_1)m-1exp

_a

By considering the above results, the probabilities of ocurrences for wave heights and the motions fishing boats in operations can be obtained.

Spectrum analysis of wave heights and the motions of fishing boats Li Power spectra of wave heights and ship motions(10)(11)

For all the data obtained, the power spectra were calculated by the above mentioned method. e power spectra for beam and quartering seas are shown in Fig. 7, and the statistics of these data are en in the included Tables.. In considering the characteristics of the whole calculated spectra, it was md that for the rolling motions, the peaks of power appeared as ship's natural frequency; but that for

pitching and heaving motions, the peaks of power coincided with those in the wave spectra of their quencies.

20107565

4 3

-

42-Wave H.(Q) Exp. No. t 'L 20 m

a

r mean x2 test Wave H. 2.1 2.7 0 1.444 12.560<x20.70(1 7) = 13.531 Pitch 1.8 12.6 0 3.601 S.915<x2 o.3o( 9) = 10.656 Roll 1.9 79.8 +1.5 8.781 8.395<X20.30( 8)= 9.524 Heave 1.6 1.6 0 1.202

6.11(2o30( 6)= 7.231

R. Wave H. 3.0 1.2 +0.2 0.948 9.478<x20.70(I4) 10.821 No. Exp. 102 124 17 ° 0.09119 5.19c. 3.83ec. 36 -"- 0.2680 11.37 3.68 30-'-- 1.0019 6.62 4.53 Toz 12.

rr.

0.1002 5.08ac. 4.03..c. 0.30110 5.09 4.26 0.67011 6.28 4.69 0.9495 5.50 4.01 ;ec. Wave H.( Bm) 2sec.

20 107565

4 3

300 ,."-... , - I

-dej -

Roll.(BirO Exp.No. O 102 124 1.6-o- 1.7067 6.24.ec. 4.36..c. 8.4979 6.46 5.46

i'

p' a 1g 100 J: ' i. ii 200

20 107.565

4 3 Fig. 7(c)

Exp. No. o.? 102 T24

A

j \

IL

'

o. Zsec.

-

43-m2sec Heave.(Q) Exp. No. 102 124 17 '° 2.5858 6.06.... 4.47.-.. 36 10.5054 6.92 6.00 30 O- 'i.0532 7.37 6.96 -s ce

20 107565

4 3 Fig. 7(d) Exp. No. 102 124 17 -o- 0.5028 5.20.... 3.49.... 36-z-- 4.1505 6.27 5.21 30--.-- 5.9273 6.25 5.08 o 20

107.565

4 3

Exp. No. loi Ti.

17-.- 0.0491 6.2S.. 4.56...-36-.-- 0.2258 6.80 5.91 S')-.-- 0.9253 7.58 5.98. Fig. 7(h) 2sec. 2sec. t _{84-.-- 22.2579 7.79} -6.56 P! I ¡

t'

t 79--- 30.2367 7.37 6.65

'I

I' t'

I'

Exp. No. 102 124 16o- 0.5611 5.13.ec. 3.72zec.

43--

1.9824 5.18 4.27 84-.-- 1.9376 5.56 4.38 79-o- 3.5649 5.79 'a.72. 16-O- 0.0586 5.85..-. 9.83..c.

43-

0.1992 5.58. 4.81. 84-.-- 0.5523 6.85 5.24 79-t.- 0.7266 6.67 5.40 -20 107.5 6 5 4 3 2sec. Fig. 7(g) rJsec Heove.(Bm) 5 2sec. 20 107.5 6 5 4 3

Fig. i(e) _{Fig. 7(f)}

2sec.

.2.2 Frequency response characteristics of fishing boats at sea

For the encountered angles between waves and fishing boats, the frequency response functions ere calculated. The results of these analyses are shown in Fig. 8.

a z 3 o 3.0 HEAVE. (8m)

.

21) _107.56 Exp.No. li3

Sii

Thxoay(o.s.o.) . -s 3 o 20 _{107.56 3} 2sEc. 2sEc.

Fig. 8 Frequency response functions of ship's motions

In the whole aspect of these results, it is remarkable that the values of coherency and reliability vere good in regard to the heaving motions in the frequency range under 0.25 Hz (above 4 sec period), ee Fig. 8. In these analyses, it can't be said that the estimations of frequency response functions were ood enough for practical use in all cases. But, for the heaving motions, it can be said that fairly good stimations of frequency response functions were obtained. For example, in Fig. 8, it can be seen that he coherencies were above 0.7 and the reliabilities were below 0.3 in the frequency range from 0.25 Hz o 0.2 Hz (in periods from 4.0 sec to 20.0 sec) in the heaving motions for beam and quartering seas. 'hen, when the frequency response functions were calculated by the strip theory, so called, O.S.M. iethod (shown in Fig. 8 by a solid line), it was found that the amplitude response in both cases were Lmilar, especially in that of the heaving motions, but that there was some difference in each amplitude

sponse in the frequency range from 0.167 Hz to 0.25 Hz (in periods 4 sec to 6 sec) for a beam sea. 'he effects of fishing gear during fishing operations were not considered in the calculations by the strip

ieory, and it may be assumed that the above mentioned difference would be affected by them.

.3 Comparisons of the obtained spectra and the calculated spectra

Using the relation between the input spectrum, the frequency response function and the output pectrum, we calculated the heaving spectra, as shown in Fig. 9. These spectra were similar in form. The ifference of the values in the heaving motion may be considered to be the difference of the measured osition of the heaving and the center of gravity of a fishing boat in its heaving motions.

-

44-Exp. No 1.0 ,- 17°

.- 36 o

30 T HE OR V ( o s . N. ) 20 107.56 5 ii '/2- Exp.Mo. 36 O-0/2 'z s 's o 000000 Fig. 8(b) i 20 1 3.4 Estim of shii Based ing boats013 spectra wer heaving ma motions are division of the averaged tioned meth the empirico in a followi spectra were and heaving i The m same type w and theirSpe

Fig. 11, th

shown. The were obtain given as follo For rolling m S(w)/(Hs/ exp (-21 For pitching S(w)/(Hs/ exp (-11. For heaving S(w)/(Hs/

exp (-Il.

2sEc. 20 107.56 5 ii 3

3.4 Estimation of a numerical spectrum model

ofshipmotions(l2) 0.1

Based on the spectra of the motions of

fish-ing boats obtained from observed data, the average

spectra were deduced for the rolling, pitching and heaving motions. These spectra in the rolling

motions are shown in Fig. 10, normalized by the .05

division of Hs values. In Fig. 10, the solid line is

the averaged spectra obtained by the above

men-tioned method, the dotted line was calculated by the empirical equation of the Gaussian form; but

in a following sea, the experimentally obtained spectra were fairly off the solid line in pitching

and heaving motions.

The measured data for two bull trawlers of

same type were obtained during fishing operations, and their spectra were calculated and averaged. In

Fig. 11, the spectra for the rolling motion are 0.1

shown. The non-dimensional spectra each motion were obtained by the least square method, and '

given as follows: .

For rolling motion:

S(w)/(Hs/c.A,l) = 0.08301 .05

exp (-21.325(wo - 0.9855))

For pitching motion:

S(c...)/(Hs/wi) = 0.06336 exp (-11.837 (wo - 0.976 1)) For heaving motion:

S(w)/(Hs/w1) = 0.06467 0 exp (-11.677 (w0 .0.9755))

-

45-deg?se .20 _Pltch(H) Roll OH

.8w

8m

'Q

OE5 o Tsoav(o..,i.) EXPERIPENT I

Fig. 10 Normalized spectra

1.5

20 1065 4

3 2sec. 20

107.565

4 3 2sec. Fig. 9 Comparison between observed spectra and calculated spectra (a), (b)

46-I

i

10) Nishinc Jap. Inst. Na Il) Nishinc Jap. Inst. Na 12) Nishinq Jap. Inst. Na I ere

Hs: Significant value of the motions of the fishing boats which would be deduced by significant wave heights or r.m.s. values of wave heights

The average circular frequency encountered wave and ship in heaving and pitching motions, and the natural frequency in the rolling motion

nclusion

e objects of the studies were to clarify the behaviours of fishing boats during fishing operations at by making field measurements, and using statistical methods as stationary stochastic processes in data analysis. The following results were obtained:

The maxima of the motions of fishing boats and wave heights were distributed according to leighs distribution functions. The r.m.s. values of maxima of the motions of fishing boats and wave

ts in the 104 experiments were distributed according to the Weibul distribution function. The use hese results made possible the numerical forecasting of the average maxima motions of fishing boats

waves during fishing operations at sea.

The frequency response functions of the motions of fishing boats to ocean waves were estimated the cross spectrum method. Then, the motion spectra of fishing boats .could be calculated by the re-on between a ship's motire-ons and the waves, through the frequency respre-onse functire-ons.

A numerical model of the motions of fIshing boats was estimated. These results made possible the diction of the motions of fishing boats during operations at sea by statistical meanings. These results y be used for the same type of bull trawlers on the East China Sea.

Rèferences

I) Kawashima, R., Analytical studies on the maneouvering of ships in rough sea Par 1, Jour. Jap. L.Nay. No. 15, 73-79 pp, 1956

Kawashima, R., Analytical studies on the maneouvering of ships in rough sea Part 2, Jour. Jap. L.Nay. No. 16, 73-80 pp. 1957

Iwai, A., A study on "Heaving to", Jour. The University of Mercantile Marine (Natural Sciences)

.7,1956

Jap. Soc. Nay. Arch., Proceedings of simposium on seakeeping qualities of ships, 1974

Nishinokubi, H. et al, On the seakeeping qualities of a fishing boats by field measurement II, 1. Fac. Fish. Nagasaki Univ. No. 40, 39-47 pp, 1975

S) Cartwright, G.E. et al, The statistical distribution of the maxima of a random function, Proc. Roy. London, Ser. A, Vol. 237, No. 108, 212-232 pp. 1956

7) Jasper, N.H. et al, Statistical distribution pattern of ocean waves and of wave.induced ship stress motions, with engineering applications, SNAME, Vol. 64, 375-415 pp, 1956

3) Akaike, H. et al, Studies on the statistical estimations of frequency response function., Ann. Stat. Math. Supplement III, 102 p, 1964

) Nishinokubj, H. et al, On the seakeeping qualities of a fishing boats by field measurement III., r. Jap. Inst. Nay. No.55, 1-6 pp, 1976

.- - _7e-k .-.._- -:;t .

41 r,..

-,

k

Nishinokubi, H. et al, On the seakeeping qualities of fishing boats by field measurement IV, Jour. Jap. Inst. Nay. No. 56, 77-89 pp, 1976

Nishinokubi, H. et al, On the seakeeping qualities of fishing boats by field measurement V, Jour. Jap. Inst. Nay. No. 56,91-100 pp, 1976

12)Nishinokubi, H. et al, On the seakeeping qualities of fishing boats by field measurement VI,Jour. Jap. Inst. Nay. No. 57, lOi-105 pp. 1977