Observations made on board of Dutch ships

(1)

Latz,

p.

Technjscpe

De lit.

Observations made on board of

Dutch ships.

(2)

OBSERVATIONS MADE ON BOARD OF DUTCH SHIPS

by

Ir. R. Wahab.

NETHERLANDS SHIP MODEL BASIN PAGE

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NETHERLANDS SHIP MODEL BASIN WAGE NINGEN

1. Introduction

*

In 1958

the Panel on Seakeeping Research of the Netherlands Ship Model Basin invited the Butch Shipping Companies to introduce a "Journal on ship behaviour at sea" aboard their ships.

By introducing this Journal it was tried to obtain an

insight into the following aspects:

- _{the response of the ship to the sea and wind}

- _{the reactions of the ship's staff on the behaviour of}

the ship

- the state of the sea as a function of location, time and other circumstances.

* The Panel comprises representatives of:

shipping companies, shipyards, the Technological University of Deift, the Hydraulics Laboratory and the Netherlands Ship Model Basin.

Report No. 67-090-WO

PAGE

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NETHERLANDS SHIP MODEL BASIN WAGEN IN GEN

2. The collecting of the data

The observations entered in the Journal were made with the instruments normally available on board a ship.

Partly the data were obtained by visual observation.

The captaina of the ships were advised to use the Journal twice a day.

Not all of the data obtained in this manner have a high degree of accuracy. It was expected, however, that this lack of accuracy night the compensated by the large number of observations.

Every observation consists of 34 data. The large number of data thus obtained made it necessary to use mechanical means for their digestion. For this reason all observations

were coded in igures.

Between 1959 and ₁₉₆₄ 60,000 observations have been made on board of 243 ships, representing about 40 per cent of the Dutch merchant navy. Figure 1 gives the size of

these ships.

Report

_{No. 67-090WO}

PAGE

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NETHERLANDS SHIP MODEL BASIN WAGENIN GEN

3. The analysis of the observations

The large number of observed quantities and the

rather complicated coherence among them made it necessary

to perform the analysis in stages; every next stage being

strongly dependent on the results of the previous one.

At present a first analysis has been made of the observations

on the state of the sea and on the conditions which may

make the captain decide to change course or decrease speed.

The occurrence of chanRe of course and/or speed reduction

In adverse weather the captain may decide to change

course, to decrease speed or to do both to reduce the

severity of the ship's behaviour.

Assuming that the reactions of the nautical officers of

the various ships show

a certain uniformity, the quantities

in which these reactions are expressed may be treated in the

same way as the purely physical behaviour of the ship.

In the Tables I and II the number of times speed was

reduced

or course was changed is given. It is conspicuous

that on the North Atlantic ships of ¿i-00 - 500 feet length

had to slow down or change course most often while on the

Indian Ocean the ships of 300 - 350 feet length had the

largest difficulties.

The arguments advanced by the nautical staff for their

decision to change course

or to slow down is given in

Figures 2 and

3

. In

the Figures the number of times every

argument was used is given as a percentage of the total

number of observations involved. In most cases a combination

of causes was put forward. Therefore the sum of the

percentages exceeds 100. As could be expected the occurrence

of phenomena like shipping water, siaimmiing etc, which are

connected to the longitudinal ship motions generally lead to

a speed reduction.

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NETHERLANDS SHIP MODEL BASIN WAGEN INGEN

Report No. 67-O9O-WO PAGE_LI-.

Severe rolling leads mostly to a cha.nge of course. For one ship type ,Victory ships,the mean speed is given as a function of the observed wave height in Figure 4.

This Figure shows that in severe head seas the average speed attained 'by these ships is about one-third lower than in

calm seas.

Sea and wind conditions

Figure ₅ indicates that the mean observed height of the swell corresponds very well with the observations collected

by Roll [i] .

This is contrto the wind waves.

Figure 6 indicates that the variance of the observed wave height in not significantly different for wind waves or for a swell.

Figure ₇ also suggests that the waves which have been designated

by the observers as swell correspond to the observations of other

investigators.

However, Figure 8, indIcates that one should be very careful in considering the wave height, since the observations taken on board of small ships clearly differ from those taken on large

ships. From the above it nay be concluded that it is very

difficult to find a single parameter which represents the

character of the sea sufficiently accurate to serve as a basis for a further analysis of the data on the behaviour of ships

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NETHERLANDS SHIP MODEL BASIN WAGENNGEN

4. Concluding remark

The digestion of the data has

consumed much

time and. is expected to

consume much

more. Only a selection of the first

results

_[4] are presented here. It is

hoped

that

in the near

future a much more extensive report can be presented, which may contribute to a clearer insight into

the behaviour of a ship at sea.

PAGE

5.

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PAGE

6.

NETHERLANDS SHIP MODEL BASIN WAGEN INGEN

References

: Roll, H.U.: Die Grasse der Meeres wellen in

Abhngigheit von der Windstärke. Einzel-veröffentlichung Nr. 6,

Deutscher Wetterdienst, Seewetteramt,

Hamburg 1954.

2 : Brooks, R.L. and N.H. Jasper: Statistics of wave heights

and periods for the North Atlantic Ocean. David Taylor Model Basin, Report 1091, September

_1957.

3 : Report of Committee No. I on environmental conditions.

Proceedings of the International Ship Structures Congress,

July 1964.

Stijninan J.J.: Eerste uitwerking van het Journaal gedrag

in zeegang.

Report No. 66-027-WO of the Netherlands Ship Model Basin, Wageninen,

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TABLE I

Observations with change of course and / or speed

reduction z m -4

I

m ,- >

>0

øv,

r!, V!

z'

z. I II III

1+11+111

Combined speed-Speedreduction Total Shiplength Speedreduction Change of course

reduction + change and / or change

number of

of course

observations

nunber percentage ximber percertage

number percentage numrpernte

300,-350'

123

1.4- 74-0.8 36 0.4-233 2.7 871I2 4-00' -450' 343 2.6 14-7 1.1 100 0.8 590 4.5 13082 500e _550}.

133

1.0 28 0.2

36

0.3

197

1.5 13433 600'-750'

3S2S

C-)

i

300'-350'

¿44 1.1 50

1.3

17

0.4

111 2.8 3925 400' -450' 269 4.2 108 1.7 53 0.8 430

6.7

6353 5001_550t}

69

2.2 16 0,5

17

0.5

99

3.2 3062

o

600' - 750' ¡.33 yo

Z

300' -350'

32 4.7 2 0.3 3

0.4-37

5.5 674 400' -450' 18

0.6

8 0.2 9

0.3

35 1.1 3174-sooI_550t} 16 0.6 3

0.1

0

19

0.7 2868 p' 600'-750'

Z

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TA13TE II

- Change of course and / or speed reduction on the North Atlantic.

o hi c-P o s o.'

o

I

II

III

1+11+111

TotJ. number of observations

Speed reduction

Change of course

Combined speed reduction + change of course Speed reduction and / or change of course

number percentage number percentage number percentage number percentage

East bound West bound

102

277

1.6

4.1

89

85

1.4

1.2

25

62

0.4

0.9

216

424

3.3

6.2 6540

6800

(11)

TABLE III

-Change of course and

I

or speed reduction of Victory ships.

NETHERlANDS SHIP MODEL BASIN

WAGENINGEN

PAGE

9.

Bow seas (wave direction II, see Figure ii-.) Beam seas (wave direction III, see Figure

14.)

Quìrtering seas (wave directior. IV,

see Figure

4.)

Following seas (wave direction V, see Figure 4.)

Head seas (wave direction I,

see Figure 4.) Draft forward (in) I II III I + II + III Total number of observations speed reduction change of course

combined speed reduction +

change of course speed reduction and / or change of course 2.40 - 4.50 4.50 - 6.00 6.00 - 7.20 7.20 - 8.70 number percentage number percentage number percentage

number percente

112 518 273 580 15 33 11 15 13.Ll 6.4- 4.0 2.14-O I 5 7 O

0.2

1.8

1.2

2 10 6 7

1.8

1.9

2.2

1.2

17

1-4 ₂₂ ₂₉ 15.2 8.5 8.1 5.0 2.40 - 4.50 2 2.1 1 1.1 0 0 3 3.2

95

14.50 - 6.00 12

2.3

8 1.5 e-4-0.8 24 14.6

519 6.00 - 7.20

2 0.7 9 3.2 1 0.1-12 4.3 281 7.20 - 8.70 6 1.4 8 1.9 5 1.2 19 4.4 431 2.40 - 4.50 0 0 0 0 0 0 0 0 90 4.50 - 6.00 2 0.5 1 0.2 0 0 3 0.7 438 6.00 - 7.20 0 0 1.6 0 0 3

16

191 7.20 - 8.70 2 0.5 9

2.5

1

0.3

12

3.0

396

2.40 - 4.50 2 2.4 0 0 0 0 2 2.4 85 4.50 - 6.00 0 0 2 0.6 0 0 2 0.6 3140 6.00 - 7.20 0 0 2 0.7 0 0 2 0.7 285 7.20 - 8.70 14.

0.8

12

2.3

1

0.2

17

3.3

518

2.40

-4.50 I

27

O O o 0 I 2.7

37

4.50 - 6.00 0 0 i 0.6 0 0 1 0.6 1614 6.00 - 7.20 0 0 1 0.8 0 0 1 0.8 126 7.20 - 8.70

6

2.3

3 1.2 5

1.9

14 5.4 259

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75 50 25 o 300 400 500 600 TANKERS OTHER SHIPS SHtP LENGTH in ft. 700 800 FIG. i

(13)

e-z

W (J W Q-300ft.< SHIP LENGTH <350 ft. 8,7L.2 OBSERVATIONS

z

o

Q-(D Z

ZW

L) (D

z

e--

-

_L) (D (D

z

--

I

>

o

t

oO

Wo

Q

Wz

W W

Wz

LL

o

(D<

z0

-o

1W

WO

FI G. 2

CHANGE OF COURSE ANO SPEED

33 OBSERVATIONS CHANGE OF COURSE 50 50 OBSERVATIONS SPEED REDUCTION 122 OBSERVATIONS 50 25 50 25

(14)

50 25 o 50 25

o

z

I

L) Q-SHIP LENGTH > 500 ft. 13.433 OBSERVATIONS 36 OBSERVATIONS r i

CHANGE OF COURSE ANO SPEED

CHANGE OF COURSE 18 OBSERVATIONS SPEED REDUCTION 129 OBSERVATIONS U)

z

o

z

o

I- Q-a:

u

(-n w

0

a: w

o

z

L) a: w a: L) a: w

I-4

u-o

a: w

I-4

LL

o

z

Q-I

(J) a: w

z

4 o

z

-D

4 o

-J

u

w

o

z

-J -J

o

z

I

L)

04 wo

-z

w

I

a:

a: D

w

u->

o

a: Q-

00 w o

U) z

50

z

w () a: 25

(15)

.

VICTORY SHIPS

N

2.5 5.0 7.5 HEIGHT OF SWELL

in m

FIG. 4 Wave direction Wave height

in m

0.25 -1.25 1.25 -2.25 2.25-3.25 3.25-4.25 4.25-5.25 5.25-6.25

625-7.25 I 1.03 538 260 102 41 24 16 E 433 549 236 107 43 16 8 374 383 1.95 484 208 186 77 91 19 35 9 21 1, 9 219 216 81 37 15 1. 6 15 u-I o C C 10

o

w w Q-(I)

z

4

w

(16)

E 7.5 2.5 s io WINOFORCE IN BEAUFORT FIG. 5

MEAN WAVE HEIGHT

ROLL [1] NORTH OBSERVED BY ATLANTIC OCEAN

/

/N.

/

I

MEAN OBSERVED WAVE HEIGHT SWELL s

1/NWAVE

MEAN OBSERVED HEIGHT WIND WA VES s

I.-I

(D LU

I

LU

>

4

(17)

I-z50

w L) w Q-g 100 o o loo

I.-z

5o w Q-o

-'7/,

3

//

,4(

_/

il

¡s,(

III

/ ,

BEAUFORT 6

Il/i

II

/

I

i"1/

/1/

II/y

WI NO WAy E S

-BEAUFORT

3 ,/ /

1

/

/'

III

/

//

6 SWELL

OBSERVED WAVE HEIGHT

in m.

FIG. 6 BEAUFORT NUMBER OF OBSERVATIONS WINOWAVES SWELL 3 14,841 12.541 4 13.582 11,713 5 _7.763 _6.808 6 _4,054 _3.630

25

50 7.5 O 25 _5.0 _7.5

(18)

0.1 1 1.5 2 3 HEIGHT

in m

4 5

6 789t0

PERIOD in sec. 15 20 FIG. 7 30 40

/

17 /

/'

/5/

/

///

/

1 I

i

//

A

/

;y.4

/

'A

HEIGHT

/'4

PERIOD

/.

'i'

1'

/

_I

N.S.M B. 20.934 OBSERVATIONS

[2]

115,064 C.

[3]

903.241 11) 50.396

0.1MB.

I.S.S. ROLL 90 85 80 70 60 50 40 30 I-w L) LU a-10 s 9 9,9 99.8 99.5 99 98 97 95

(19)

loo

/

SHIP LENGTH >500 ft 1259O OBSERVATIONS SHIP LENGTH<350ft 8.398 OBSERVATIONS 25 _5Q ₇₅

OBSERVE O HEIGHT OF SWELL in m.