Full scal test on sinkage of super tanker through shallow water

3 JULI 1575

ARCHIEF

Lab. V . Scheepsbouwkunde

Technische Hogeschool

Deifl

Full Scale Test on Sinkage of Super Tanker

through Shallow Water

Atsutoshi YAMAGUCHI. Keinosuke HONDA

Satoru MATSUKI. Minoru HIROTA

and Kiyoshi HARA

n

F

IÖJ-

m

-X ¥

la

mn-* mm' m^m^^^mi

FuU Scale Test on Sinkage' of Super Tanker

through Shallow Water

Atsutoshi Y / ! J V [ A G U C H I , Keinosuke H O N D A Satoru M A T S U K I , Minoru H I R O T A and Kiyoshi H A R A

( B g a 4 3 f p i j j i o B g ï B )

Abstract-During the preceding year 1964 and 1965, we carried out a series of model tests concerning the .smkage of a very large vessel underway through the restricted channel.

_ The detaiis of our work were reported last year. This is a report about the f u l t scale test of the

?^"^TtT^

P r

t^'T'"'"*'^'^^

A b u j e z ^ a Flat (Off Mina A l Ahmad, i n K J W A I T ) m Persmn Gulf, August and October in 1966. The water depth of locality was in region of

12 m. The actual ship tested is "Tokusbima-maru" to N . Y. K. Line ( D . W. 123,9891 Summer)

The change of the bow sinkage was recorded by an echo-sounder which received the echo f r o m the o T ' ^ O m t n ï ' ' " ° ' ^ ' ' ' ^ ''^^ " ' " ^ ^ Then, authors substituted the infinite shallow water f o r an "Effective" channel w i d t h and ^estimated a cnttcal speed of touching bottom, and judged that the "effective" width is 8 times as much a^ the beam oi a ship considenng data obtained hy both model tests and f u l l scale tests.

(Received 10th, Jan., 1968)

I . mTRODUCTION

Authors had reported the bodily sinkage of vessel underway in the shallow water by the model tank tests in the previous paper, and after that we performed a series of tests on the bodily •pinkage of an actua! ship and a model siiip o£ the same type. Through these tests, we research: ed how to apply the value of bodily sinkage, which was got by the tank tests, (o that of the, actual ship under way in the shallow water. The f u l l scale tests were performed aboard the super tanker "Tokushima-maru" to N . Y. K. Line i n the shallow water off Ahmad; in Persian Gulf in 1966.

I n this paper, we reported the procedure and the results of the f u l l scale tests f o r the bodily sinkage, and studied the 'coilrelation between an actual ship and .a model f r o m the results of our tests of a few years. A s a conclusion, our pro-visional value of the bodily sinkage of the vessel underway i n the infinite shallow water could be made useful as one of tbe important materials to

decide the passage-depth about the safe navigation, of very large vessels such as D. W . 100,0001 when the Passage Dredge -in the Inland ,Sea ,of Seto i n our- country was practised.

ü F U L L SCALE T E S T PROCEDURE 2; Actual Vessel Tested

Our actual) vessel tested is a super tanker " T o -kushima-maru" belonging to N . Y. K. Line.. Her principal dimensions .are as following ;

Gross Tonnage Net Tonnage Dead Weight (Summer) Length O. A , Length P- P. ( L p p ) Breadth ( B ) Depth ( D ) Max. D r a f t (Summer) Max. D r a f t (Test) Displacement (Test) L p p / B L p p / D Cb 67,653.40 t 45,057.64t 123,989t ,270.10 m 256.00 m 42.50 m 22.00 m 15.,832 m 15.000 m 142,777 t 6.fl23 11.1636 0.808 - 15

A . Y A M A G U C H I . K. HONDA, S.

Main Engine Turbine 24,000 ps

Propeller 105 PRM X I

Max. SpeedjBuU Load) Trial 17.20 kt

Service 16.05 kt

Delivery April 25. 1966

2. Test Locality

Desired conditions of the test locality ate ;

a ) The flat sea bottom along straight line,

where it is about 20m deep.

b ) The water prevented from the strong wind

or current.

c ) The water of few ships and fishing boats.

Searching on thU chart for any water of such

good conditions for the test, at first we selected

the waters, off Piai, off Cape Rachado, and near

M A T S U K I , M. H I R O T A and K. H A R A

cause of the rough sea bottom (Fig. 1). Then our

main test was fulfilled within Abu Jezza Flat

(Fig. 2) ofE Mina A l Ahmadi in Persian Gulf,

where we found all proper. The supplementary

test was carried out at Horsburgh Bank to the east

of Singapore Strait. A part of the under-keel

clearance record at Abu Jezza Flat is shown in

Fig. 3. Such a flat bottom and an identical depth

shown in this photograph continued more than 5

sea miles long.

F i g . 3. Sea bed condition at Abu Jezza Flat.

F i g . 1. Sea bed c o n d i t i o n at One F a t h o m Bank.

One Fathom Bank in Malacca Straits.

Prelimina-ry test, however, found them improper mainly

be-B.A.

a^<i

HO.

m

^\

A ^

\ U u Al

j

....

B

ABU J S i U tut Al Kubr

'00^

_ 25" - 00'

fl

1

3. Measurement Procedure

a ) Sinkage of Bow

A supersonic vibrator (24kc/s) was fitted at the

end of the boom projecting 6m ahead tbe bow

along the center line (Fig. 4). An echo-sounder

recorded the distance between the vibrator and

the sea surface ; it is usually about 10 m high in

full load conditions.

Before our ship entered the test

locality, she was stopped and the

reference values of the draft, the

trim and the distance were read

and recorded. The how sinkage

is different between the distance

on test and the reference vakie.

In this case, some errors must

be introduced by the height of

the bow wave, as shown Fig. 5,

and the height was estimated on

the basis of the model test and

was corrected.

l<ai«.48 -15 » < f - 5 0 4 a - 45

F i g . 2. Locality of Full scale test

F i g . 4. Bow-boom.

not under way Under way

F i g . 5. Procedure of measuring the fore sinkage. b ) Change of Trim

A long U-tube was installed on the upper deck. It consisted of (a) three vertical pipes of steel (lOOmm^i, along the center line, in bow, midship, and stem), (b) a long transparent connecting tube of Polyvinyl chrolide (47iimi(ii, 250 m long, along starboard side), and (c) three valves aiming adjustment of the vibration of the free water surface. The difference between the height of

water surface in bow and stern is proportional to the trim of the ship underway. A supersonic vibrator was put on the top of the vertical pipe in the stern, to get a continuous record in the bridge.

F i g . 6. Midship vertical pipe for measuring of trim. 100 . n 3 t « i l plp« _' 91.4 •• 'S^"»•ïï^it5r X-Jer_BchQ Bounder 07 laa v i n y l tub*

Npzz!..J

Fijf, 7. Arrangement of

A. YAMAGUCHI, K HONDA, S.

c ) Depth of Sea

Unde-rkeel clearance'was'measured-and

record-eiJ continuously with the accuracy of ± 5 c m by a

precise echo-sounder, the vibrator of which was

set on the bottom plate just below the

bridge-The sea depth was calculated from the

under-keel clearance with consideration for draft!;

sink-age and trim.

d ) Speed of Ship

Generally speaking, we have no effective

mea-suring device of the actual speed of the ship in

the shallow water, because S A L log (pressure

type) is drawn up into the hull- We set a hood

with motor-drive camera on the Radar screen,

and threw over-board many carboard cartons of

1 m" filled with Aluminuim foil as Radar

re-flectors. The photographs of the screen were

talcen automatically in succesion We expected to

.decide, on the speed from the time-intervals of

the reflector echo passing range circles.

Un-fortunately, however, films were wrong,- so we

estimated the speed from revolution of actual

propeller at last

MATSUKI, M. H I R O T A and K . HARA

m. M O D E L T E S T P R O C E D U R E

Z, Model Ship and Test Arrangement

The model ship used in Lbe tank test was made

of wood and 2 m in Lpp, that dimensionally

cor-responded to 1/128 of an actual ship used in the

full scale test Our experimental works were

made in the shallow water tank in the laboratory

(37.5m long, 2.0m wide, and 1.2m deep fnside)

as shown in Fig. 9.

Fig.. &. Hood with camera on Radar.

F i g . 9. Experimental carriage of tank test.

Fig. 10. Model T2

The bodily sinkage-was- measured as the

rela-tive change of distance between the model and

the horizontal measurement platform, then the

- 18 —

Full Scale Test on Sinkage of Super Tanker through Shallow Water

sinkage was shown by the records on a Direct

Recording Oscillograph. The water depth was

not changed by rise and fall in the provisional

bottom plate attached to the tank, but by increase

or decrease of the water level in the tank. To level

the tank bottom, ten sheets of steel plates (2000mm

long, 600 mm wide, and 5 mm thick) were laid

at the tank bottom and adjusted within +0.5 mm

of level error to the level of the rails which were

fitted on the either wall of the tank, and which

were adjusted itself within ± 1 / 2 0 mm of level

error.

F i g . 12. Procedure of measuring the

height of bow wave.

2. Height of Bow Wave

If the water level just below the vibrator rose

even a little in the full scale test, the value of

sinkage, which was calculated only from the

equation of (_SL-V) as in Fig. 5, would be larger

than the true sinkage. Therefore, a series of

model tests were performed to measure the height

of the wave in front of the bow.

A thin steel plate (250 mm long, 70 mm wide,

and 0.1mm thick) was painted as checked

co-lours (Fig. 11), fitted to the towing carriage and

towed together with the model ship, changing

speeds and the water depth. The height of the

bow wave underway was measured by many

photographs of this plate taken from the side of

the carriage. (Fig. 12)

Tbe heights of the bow wave just below the

point "A" were shown such as Fig. 13, and those

were influenced with the surface tension so they

had a little error of about 0.5mm.

c . l . I m i m , 01

C.IO 0.20 a,y> d.io 0,50 0,60 0 . 7 0 0.8O 0,90»

Fig. 13. Results of the height of bow

wave measured.

- 4

7 ^

I t M l ' ^ t » t I t O l c T O X O . l M )

Fig. 11. Plate for measuring the height

of bow wave.

IV. T E S T R E S U L T S A N D C O N S I D E R A T I O N S

1. Comparison hetween Full Scale Measurement

and Similar Model Test Results

The results of the full scale measurement were

shown on Table 1, and these data were plotted

together in the results of the tank tests with the

similar model at W / B = 6 in Fig. 14, 15 and 16.

The speed of an actual ship was estimated from

the propeller revolution as said above,

disregard-ing the movement of a Radar reflector because

of the indistinctness of the Radar echo, so the

estimated speed was not so certain that we kept

some range for speed

-No.

A. Y A M A G U C H I , K. HONDA, S. M A T S U K I , M. H I R O T A and K- H A R A

Table 1. Results of full scale

measurement-f T ^

3 4.

Position

Off MINA ALOff MINA ALj

A H M A D I ' A H M A D I

22,4m

Depth of sea

(H)

Sea condition i Very smooth

I

Wind direction '

and force

WNW-1

23.9m

Smooth

WNW-2

Fore idraft

After draft

Mean draft

Trim

Estimated speed

15vl6m

15>,16m

15.16m

0

15.16m

15.16m

15.16m

0

Off MINA ALI

A H M A D I

33,8m

Smooth

WNW-2

15.16m

15.16m

15,16m

0

C A B L E B A N K I HORMUZ

( P E R S I A N i S T R A 1 T ( P E R

Off MINA A L

A H M A D I

G U L F )

80.1m

Smooth

WNW-3

15,16m

15,16 m

15.16ra

0

S I A N G U L F )

115m

Smooth

WNW-3

22.8m

Calm

0

15.16m

15.16m

15.16m

0

14,60-14,98Kt 14,60-14,98Kt; 14.75-15. llKtj 14.75-15.llKt i 14.75-15,UKt

Bow sinkage* ' 2.71m

Mean sinkage ' 2.15m

Change of trim' 1,13 B / H

H/d

1.47

2.45m

1,96m

P-97 B / H

2.04m

l,.68m

0.71 B / H

1.53m

1.22m

0.61 B / H

14.90m

15.12m

15.01m

0.22 B/'H

1.56ra

1.25m

0.63 B / H

O. G. 15.3Kt

Remark

i r.p.m. 92-93

1,58

O. G. l ö . l K t

r.p.m. 92-93

2.23

5.,31

7.62

O . G . 1 5 . 7 K t i O . G . 1 5 . 5 K t O . G . 1 5 , 5 K t

r . p . m . 92-931 r . p . m . 92-93 I r.p.ni. 92-93

9.75-10.05Kt

1.22m

1.03m

0.39 B / H

1.52

L O G lO.OKt

r.p.m. 62-63

* Remark : Bow sinkage of this table means change of dist^ince between vibrator of supersonic

distance meter (13.34m from F P ) and sea surface.

Cond. : F u l l Trim : V/B : 6.025

•0.25

0.50.

F i g . 14. Comparison of change of trim between modér test and fuH

scale measurement.

-S 9 10 11 Ï 2 r 1 Off M I N A A L A H M A D I 22.4m, Calm 0 West side of I N D I A 82m (chart) Calm ( S W E L L 1) 0 O N E F A T H O M B A N K ( M A L A C C A S T R A I T S ) 38.7m Smooth N N W - 2 : HORSBURGH ( S I N G A P O R E S T R A I T S ) 27. l m Smooth W S W - 2 1 D I A M O N D P O I N T ( M A L A C C A S T R A I T S ) 80.8m Calm 0 HORSBURGH ( S I N G A P O R E ' S T R A I T S ) 47.4 m Smooth W S W - 2 -14.90m 14 ..80m 14.93m 14.90mi 14.H0m 14.90m 15.12m IS.BOm 15 .,31m 15.24m 15.31m 15.24nr ia.'01in 15.. 14 m 15.12m 15^07 iii 15.11m 35v07m ,0.22B/S 0.70B/S 0.38By'S 0..34B/S 0.-416/3 0..34B/S 14. 60-14. 98K.t 15.83-16.17Kt 15.83-16.17 Kt 15.66-16.OOKt 15.83-16.17Kt 15,83J6.17Kt • 3.26 m 1.96m 2.05m 2.58m 1.86m 1.85m 2.78m 1.58m 1.68m 2.12m L 5 4 m 1.43m j 0.96 B / H 0.66 B / H , 0.73 B / H 0.93 B / H 0 . 6 4 B / H 0.73 B / H '1 1.49 5.42 2.56 1.80 f 5.35 3.15

LOG 1 4 . 0 K t LOG 16.6Kt LOG no set ^ LOG no set LOG no set LOG no set

^^^^

r..p.m. 91-93 r.p..m. 98-100 r..p.m. 98-100 1 1 r . p . m . 97-99 r . p . m , . 98-100 i r . p . m . 98-100 ;

Conn. : Full Trim : o '.V/fl : 6'>025

^^^^^^^^^^^^^^

- ^— . H/d = ^ ^ — — ~ — !. 79 (Deep). 1

— ^

1

j T-all BOale noasureaient

\

1 . I T V — 8 0

! 1

1,. _{f 1}

•0.07 O.OB O.OS O.IO 0-11 0.12 0.13 0.11,, 0,15 0.16, 0.17

Fig. 15. Comparison of mean sinkage between model test and

scale measurement.

A. Y A t J A a U C H l , K . H O N D A , S. M A T S U K I , M. H I R O T A and K. H A R A

c u l l Trim : ISS 0 SS 0.25 0,50 75

n

i.oo; 1.25 I.50L WB : 6.025

, _

₁

^ " S i ï ï i S i T , B / d - l . S Z

^

^

^

^

^

^

5.1

Pull BOale tEeasureflient 0

--0—nS8 ^ \ V—l . f l » W , 1 . . 7 \ \ 1 I l l l - ^ l . ' * s \ Froude'e nunber

F i g , 16. Comparison of bow sinliage between model test and full

scale measurement

a ) Change of Trim

According to Fig. 14, the actual ship trimmed

a bit more remarkably than the model ship at

the depth of H/d =5 and more, though it was

expected that the trim of a ship navigating in

open sea was smaller than that of the model

tested in narrow channel. The change of the

trim of a ship seems to be unchangeable at the

depth of H / d = 5 and more.

b) Sinkage of Bow

We calculated the mean sinkage of the ship

from the bow sinkage and the change of the

trim, and the bow sinkage was got on the basis

of the difference between a supersonic vibrator

of the bow boom and the sea surface. Then, the

change of the distance includes the rise of sea

surface just below the vibrator in front of 13.34m

from F P .

Since the sea surface rises distinctly as Fig. 13

shows, it must be deducted from the change of

distance, to estimate the bow sinkage exactly.

Thus, the data of the actual ship at Froude's

No.=0.153 and 0.164 were shown in Fig. 17 and

18. In these figures, the mark "O" shows the

change of distance measured on the actual ship,

next mark " • " shows the value that deducted

the rise of the surface estimated on the model

test from the change of distance, and the mark

"A" shows the change of trim measured on the

actual ship.

ii.ah22

-Bow o l n i w e t tn'eo e o r r t e t t i ï Üw o f b a « « v a a t p a « ^ t « B t 1 Cttanc» o f trim ( f u l l 9eaU Bov olnVaw ( E o r r « e t e f l " I t h the h » l t f i t of ' • v e o f

voiti St ""«P

Ito» o l t i n r c o r anael t i n Mrr b i o l n o f H/a « C..0?5)

Fig. 17. Fore sinkage estimated from

the full scale test. (Influence

of depth of water)

The bow sinkage at H / t l = 5 to 7 that deductetl the rise of the surface is approximately equal to the change of trim, of the shjp: This means that the stern sinkage of a ship is nuK and the bow sinkage is equal to the change of trim. Actually, the stern sinkage of the model ship that was carried out in our tank js very-small.

. ülaV,c, ( e n - n c l . d Irtm. t h , ) i i l , h c of « V a • I . = , . 1 t . - , l l "B, OI t | . l » ^ ( r o l l a d * • In,.,Ci (aan-,,..,4 altU tna h . i ^ j i t ar of Bo.',l At a.a, a . t a r l

F i g . 18i Fore sinkage estimated f r o m the f u l l scale test^ (Influence of depth of water)

From this, i t is supposed that the values marked at H / d = 5 to 7 represent the actual bow sinkage and that the height of the surface estimated f r o m the results of the model test Ts ,as it is

A f in Fig. 13; the rise of surface o f the model is higher in the shallow water, but the blockage of charmel ( A / A ® ) is very small in the shallow water on the model test, so i t is improper to .apply all the model' test results, in .order to

cor-rect the rise of surface of any actual ship, which we think ought to be muCTi. We adopted the rise of the surface at H / d = 5 and more, to correct the actual rise in the shallow water. The cor-rected bow sinkages i n such method, which were-shown in F i g . 17 and 18, might be the maximum value of the bow sinkage of the actual ship respectively i n contrast with the speed and the

Tanker Ihrough Shallow Water water

depth-Companng the corrected bow sinkage in Fig-, 17 mid 18 with the modöl tesf results carried out in the restricted channel of W / B = 6 , 0 2 3 , it was found out that the corrected bow sinkage .of the ship was the same as the bow sinkage of model ship at 9 0 ^ speed of the actual ship. As the data of the f u l l scale measurement are of high speed lof Fn = 0.15 to 0,16, i t ts uncertain that this tendency is applicable to all speed-ranges. However, considering that sinkage at the low speed is few, there are not too many errors from the application of this speed correction.

Fig. 19 and 20 showed the estimated bow sinkage of any actual ship corrected by the model' tests, the curves must be the maximum bow sinkage, so the actual sinkage may not exceed

them-C o n n . f Full r r l .

0.5 1.0

F i g . 19. Fore sinkage estimated f r o m the f u l l scale measruement.

-A. YAMAGUCHI, K. HONDA, S. M A T S U K I , M. H I R O T A and K. H A R A

Cond. ! F u l l Trim : o *

• 12 -13 - u

Froude's number

F i g . 20. Fore sinkage estimated from the full scale measur

(Influence of ship's speed)

3. Critical Speed of Touching Bottom

According to our previous sinkage tests on the

A l , A2, A3, and T2, the critical speed

of the ship whose bow may touch the tank bottom

in the shallow water is provided as shown in

Fig. 21. At the water depth of H/d = 1^05 in the

tank the width of channel had not anything to

do with the bodily sinkages, and the bow of the

H/d l . a

model ship touched the tank bottom,

proceeded at Fn=0.7.

In this way, if the water depth is extremely

shallow, the bodily sinkage will cause a change

of the water level with in the limited space

aro-und the body of a ship, then on the model tests

in the extreme shallow and restricted water such

as the water width of W / B = 4.34, the bodily

1

1

r

.10 .11 .12

Froude' a nvjalïer

Fig. 21. The model ship's speed when her bow touches the tank bottom.

24

-sinkage had hardly anything to do with the side wall effect. However, in the case of the shallow water at H / d = l . l , the wider the channel is, the greater 's the speed at which "the bow of modet :ship touches the tank bottom. Therefore, it may be considered that the bodily sinkage of the ship underway in the infinite shaMow water is •equal to the variation of a depressed water level in the Cimited space around the sJiip, and the the critical speed o f touching bottom in the. shallow water is able to be regarded as a sinkage-phenomenon, which results from an "effective" width of the restricted channel.

a ) Rough Estimate of Critical. Speed of Touch-ing Bottom

The water flowing at a uniform speed through a canal, the same quantity of it should pass the cross-section, per unit time. Owing to the small.er area of the cross-section through a ship the ve-locity of the flow must increase there. Equation of continuity and Bernoulli's theorem for a water level are usually given by the following,.

. , . a o ^ r { ( . A ) ^ _ , } a ) where, J/i . Change of waler levei or bodily

sinkage in % of Lpp : Froude's number V / v L p p " ^

A : Normal cross-section area o f

chan-nel,

m.-A' : Cross-section area at midship

sec-tion, in.-'

A% \ Midship section area, m

-Change of water Jevel or bodily sinkage, m

•Water width of .channelU m Length of ship between perpendi-culars, m

V : Average speed of reverse flow past

midship section or ship's speed, m/s

g \ Acceleration due to gravity,, m / s '

A reasonable construction upon the correlation between the change of t r i m and the ship's speed was not to be matle distinct i n our model! tests-,, so i t was assumed that the change of the t r i m -would change in proportion to the bodily mean

W : Lpp:

sinkage at the range of the normal speed of a super tanker and that the bow would sink (1-l-e) times more than the mean sinkage. Therefore, when the bow touches the bottom, the imder-keel clearance sat midship section is equal to ^H e and •the Critical speed at which the bow touches the

bottom is regarded as such a speed as the sinkage is equivalent to, ^H e of the under-keel clearance dt midship section.

As illustrated in Fig., 22, namely, the- under-keel clearance {H-d) of the ship at rest is equal to a value AH- (l + e) of ship underway. From above correlation, the change of the water level or the bodily sinkage is written as follows

. . . L

-- -- r

F i g .

22.

The sketch shows the con> dition of miship-section when the bow just touches the bottom.

B-d

l + e .-..(2)

a.nd since A = \V-H, A^.'=B-d, arrd

A'=A~A0- JH-W=W-d{^^ A / A ' = w { ( i - - . l ) - « } m=Hld, + 1 wh. -e

)

(3>

A n d substituting for (2), (3) in (1) gives

Fn--

(4)

2 / » g ( m - ' l ) ?L. 4 = ' _ i I 3(1-)-me)-H J where, p-LppId, 9 = l / ( l - l - e )

Since equation (4) is dimensionless, i t is appli-cable to a channel and a ship of any size- The value "e", a ratio to the mean sinkage, which •subtracted the mean sinkage f r o m the bow

sin-kage w i l l he given about 0.24 as shown in Fig. 23, 24 and 25 being obtained f r o m data in the model tests, beacause these approximate values were 1.24 in model T2, 1,20 in model A l , A2 j n the shallow water Lpp wide, and were 1.24 i n model A l in the shallow water 2 Lpp -wide.

A . Y A M A G U C I I L K . H O N O A , g ^ ^ T S U K ï , M. H I R O T A and K , H A R A

•il/fi : 6.025

_

;

/

\

\

) : 1 — 1 r

1

1

1

.07 .08 .09 .10 .11 .12 .13 .1+ -15 .16 .17 rroude'a numbar

F i g . 23. Influence of the model ship's speed ontthe ratio of fore sinkage and

mean'sinkage. (model T2)

CoQd : Full ï r l n : V(/B : 6.51

1.60

1.50

1.40 1.30 1.2U 1.10 1.00 i-oBo — - — — — 1 a / d - i - i s o i . i a i '

-1 I l-lOO 1 I 1 .„ 1 08 .09 .10 . U .12 .15 .14 .15 .16 - I ' i Froude's nunber

Fig. 24. Influence of the model ship's speed on the ratio of fore sinkage and

mean sinkage (model A2)

-Cond. Tall Tria : 0^ 1.00 .10 _{.13 .1.4} .15 • U .12 froude's number

F i g . 23. fntiuence of the model ship's speed on the ratio of fore sinkage- and .mean sinkage. (model A 3 )

16 .17

b ) .Application of Above Rough Estimate to Actual Ship

By enlarging curves, of the correct boilv sinkage shown in Fig 17 and 18, the ratio of the water depth to mean d r a f t , wliere the bow touches the tank bottom, can be obtained at the range of 1.15 to-1.16. Specially, i n Fig. 17 an "effective" width of the channel wilt be regarded ahout 8 times of the beam of the ship, i f the equation (•14) is applicable lo ihe actual ship. I n other words, the correlation between the critica! speed of touching bottom and the water depth w i l l be got, provided that the bodily sinkage of the ship underway in the infinite shallow water is equal to that underway in the restricted channel whose-width is 8 times of the beam of the

ship-N o empirical data on ihe critical speed of touching bottom and on the sinkage al a lower speed of the actual ship have been obtained, so we could not make distinct the correlation hetween the above speed and an "effective" channel width. Since the "effective" channel w i d t h resulted from tire model' tests was 6.6 to 7.9 times of Ihe beam of the ship by the application of the equatiog

(14), the Critical speetl of such a very large vessel as a super tanker which under in the extreine shallow water can be estimated as shown on Table 2 provided that the "effective" channel width is about 8 times lof ,the beam of ship.

Table 2. E'siimared speed of touching bottom

H/d 1.050: 1.075| 1.100! 1.125 1.1501

0.1081 0.124 0.136j

13.2

0.145! 0.152i

14.1 14.8

Fig. 26 showed on a comparison between our estimated values f o r sinkage and C. H . Sjostromis non-dimensional curves for sinkage in the .shallow water. As shown in the figure, the estimated critical speed 'of touching bottom confirms rela-tively lo the non-dimensional curves in the in¬ finite shallow water- but the bow sinkajje of "Tokushima-maru" was plotted greater than his curves because of the weak correction of the height of the. how wave in the shallow water. 27

-A. Y A M A G U C H I , K. HONDA, S. M A T S U K I . M. H I R O T A and K. HARA O a> o 10 "Tokushima-maru"^ C.H.Sjoe.trom 0 F n - 0.10 A F n = 0.12 X F n = 0.14 •4 Fn, = 0.16 • E s t i m a t e d e peed o f t o u c h i n g b o t torn 0.5 1-0 1.5 V ( k n o t ) / / H ( f e a t )

F i g . 26. Comparison on bow sinkage in shallow water.

2.0

V . C O N C L U S I O N S

a ) Our full scale test on the sinkage could not be done in the water depth less than 1.3 times in draft for the safe maneuvering, so the maximum sinkage of the bow of D. W. 120,0001 super tanker (Lpp=256m, Cb=0.808) will not exceed the limits of the sinkage as shown on Table 3, when proceeding fn the infinte shallow water with draft 15 m.

b ) The sinkage phenomenon of the super tanker

the data resulted from both the model test and the full scale test, even if the hull forms of vessel are of a little difference.

c ) The bodily sinkage in the shallow water less than 1.3 times in draft was not easy to be estimated from the data obtained on the full scale test. However, substituting the infinite shallow water for the "effective" restricted width, the critical speed of touching bottom was estimated as shown on Table 2. Generally speaking, when such a very large vessel as a super tanker

imder-I,

underway will not he varied sharply considering

Corrected bow sinkage of full scale measurement Table 3. Hid Fn 1.4 1.5 1.7 2.0 3.0 8.0 0.09 .22% .19^ .10^ .08^ 0.10 .24 .22 .18 .15 .11 .07 0.11 .30 .26 .22 .18 .13 .08 0.12 .37 .32 .27 .21 .15 .09 0.13 .46 .40 .33 .25 .18 .11 0.14 .57 .49 .41 .31 .22 .13 0.15 .69 .61 .49 .39 .26 .15 0.16 .85 .75 .61 .49 .31 .18

Note : sinkage expressed as a percentage of Lpp — 28 —

way proceed i n the extreme shallow water of the depth of 1.5 times i n draft, she may have some dangers of touching bottom, provided that the proceeds at below Maneuvering Full Speed.

d ) Both the measure of the ship's speed and the height of the bow wave should be greatly noticed in die f u l l scale test of the sinkage mea-surement, unless other procedures are provided. A C K N O W L E D G M E N T

These tests were sponsored by Tbe T h i r d Dis-tinct Port Construction to The Transportation Ministry in our country, in order to decide tlie passage-depth f o r the safe navigation o f very large vessels based on The Passage Dredge Pro-gram in the Inland Sea of

Seto-\cknowledgment was due to " N . Y . K. Line" Shipping Company f o r the assistance of the test

Tanker through .Shallow Water at alt times.

Special acknowledgment was also due to the following staff member to " N . Y. K, Line" Ship^ ping Company for the help o f Jhe experimental

Work; Captain M r . M . Mieno of

"Tokushima-maru", her chief officer M r . T. Suzuki and her crew i n the f u l l scale test, M r . K. Sanada and .Mr. A . Kato i n the model test.

REFERENCES

J- A. Yamaguchi, K. Honda, S. Matsuki, K. Hara, and T. Noziri ; "Model Test on Sinkage of Very large Vessel Underway in Restricted Channel", The .journal of The Nautical So-ciety of Japan, V o l . 36, Jan. 1967.

2 C. H . Sjostrom : "Elïect of Shallow Water on Speed antl Trim." New York Metrojjolitan Section of S. N . A . & M . E., Sepl. 1985.