Model test on sinkage of vessel underway in restricted channel.

3 juu 1375 U b . V . bcheepsbouwkunde

ARCHIEF

Technische Hogeschool

Ml

9

Model Test on Sinkage of Vessel Underway

in Restricted Channel

Atsutoshi YAMAGUCHI, Keinosüke HONDA, Satoru MATSUKI and Kiyoshi HAR A.

(iraTn42<piJ!iDni§ji)

ABSTRACT

A series of tests were marie to investigate the effect of water depth ori the sinkage o f ships i n •straight and shallow water passage.

The model ships were 1 m, 2m, and 3m in Lpp respectively and were of the same type as a very large vessel ( D . W. 100,0001) with a bulbous bow, which has been recently launched in our country, and another was 3 m long w i t h a larger bulbous bow. The water depth of the model channel ranged from 1.05 to 2.0 times in draft, these four ships were run in it at a speed below the commercial speed of actual ships, the channel width ranged from 4.34 to 13.02 times in ship's breadth (Maximum width IS 2.0 times in ship's length) by using the model ship of the different size. The bodily sinkage at F. P. and A. P. of the towed models with propellei: current was obtained from the an.ilysis of oscillographic records under the tests.

The tank tests by model ships let us get the following facts :

a ) I n very large vessels with a bulbous bow, the bow sank more than that of stern, and even i f the depth of water became extremely shallow, excessive sinkage of the stern, what is called, SQUAT, did not occur.

b ) The initial trim had hardly affected the mean sinkage except for the change of trim underway. c ) Though the tendency of trim by the bow could be applied to very large vessels, it was not

always done to the other type of ships.

d ) The revolution of the model ship propeller had not so much effect on the bodily sinkage. e ) The bodily sinkage tested at every various speed in the restricted water, generally indicated

the same tendency as values calculated by Kreitner's method.

From the data obtained by tests on three similar models, we can predict that the maxlrhum o f normal operating speed to be permitted will be 12 knots on D. W . 100.000 t in the shallow water of unlimited width and restricted depth 1.1 times in draft

(Received 10th. Jan, 1967)

7i . I N T R O D U C T I O N

The immediate purpose of the model tank test was to obtain an information which would be of use to the Passage Dredge Program in the Inland Sea of Seto to select the passage-depth f o r the safe navigation'of very large-vessels such as D. W. 100,000 t.

When the vessels' are underway in the water of the restricted width and depth, most of the ship-hand lersi experience the facts shallow water effects that ship's speed slows down, that her manoeuvra-bitity gets worse and that the water level around

her Towers- In these effects,- hydrodynamic phe-;nomena of major importance in our study is the

bodily sinkage caused by the change-of-level around the running vessels, and the aim of our experiment is to research the limited speed of ship which may strike the passage-bottom in the water depth ranged from 1.1 to 1.3 times in draft.

Previous to the test, several searchs of the literature pertaining to the bodily sinkage had been made. I n the past, considerable study was made to the variations of the resistance of ships i n shallow water. There were very few of them

10 A. Y A M A G U C H I , K. H O N D A , S. M A T S K I and K. K A R A on the sinkage of ships under thése same

condi-tions, and they were usually limited to tests with fine model ships at high speed, and the restricted water depth also was not so shallow as our tank test. After the searching of the literature, it was known that Kreitner's article was furnished useful oh the relation of the operating speed to the bodily sinkage in the restricted water at least, and that the experimental report on the design of a ship' canal by The David Taylor Model Basin in 1958 was of much use, to discuss our test procedure.

As yet, i t is 'rtot easy to predict how niuch bottom clearance need to take into consideration for safe navigation- I n order to research more accurate estimates of the bottom clearance for the operating speed, authors carried out the model tank tests on the sinkage of ship under the same condition in actual ship.

Table 1 Dimensions of model ships.

11. rKST PROCEDURE "1 Test condition

The sinkage of model ship was measured mainly under the f u l l load condition rather than under the ballast condition, and each limit to water depth, thé speed of the model' ships and their initial trims were set as following ;

a ) The water depth was ranged from 1.05 to 2.0 times in H / d , where notation " H " is the water depth and " d " is the mean draft.

b ) Their speeds were ranged from 0.05 to 0.15 in Froude's number.

c ) Their initial trims were set 0%, ±Q.5% and -k\.Q96 of Lpp, where minus notation repre-sents trim by the head and plus 'One trim by the •stern.

2. Sek'Ctioii of model sfiips and test eqinpmenp Model ships selected in the test are four ifs shown on Table 1. Three models of them are the same type-A as shown in Fig. 1, which are the standard type of D. W. 100,000 t tanker and similar dimension differed with 3 m, 2 m and 1 mi in Lpp, and anothei is the hull with a large bulbous bow-B type.

Model No. A 3 3 3 A 2 A l Lpp (mm) 3,000 3,000 2.000 1.000 B (mm) 461.54 461.54 307.70 153.8Ö d f u l l (mm) 167.04 167.04 111.36 55.68 F-ull Disp. (kg) 185.05 195.44 54.24 6.85 L / B 6.50 6.50 6.50 6.50 L / d 17.96 17.96 17.96 17.96 Cl, 0.800 0.845 0.800 0.800 Ich ( « ) - 2 . 5 - 2 . 6 - 2 . 5 - 2 . 5 Fig. 1 Model A 2. Fig. 2 Model B 3.

Fig. 3 Levelii\g the tank bottorn.

Experimental works were made in the shallow water tank which was re-equipped with the

Model Test on Sinkage of Vessel Underway In Restricted Clmnne'i ₁₁ existing resistance tank (37.5m long; 2.0m wide

and 1.2 m deep inside). A Measurement plat-form was .attached under a towing carriage tra-velling along the rails fixed on either wall of the tank, and ten sheets of steel plate, which was 200.cra long, 60 cm wide and 15 mm thick, were laid in the measuring space 20 m long at the tank bottom, and the level of tliese plates were adjustetl within ± 0 . 5 mm of level error to the rail level: by turning many screw bolts which were fitted with the steel plates at the tank bottom, and previous to this adjustment, the leve of eitlier rail had been already adjusted, for the error not to exceed +1/20 mm to the water level. The-width of mode) channels was «anged from 2 m to 1 m by shifting across the vertical side plates consisted of a number of steel plate, and the joint between the tank bottom and the side plates was sealed by inserting a rubber strip under the edge of the plates in order to check the pressure leak-age-of the channeD insidej

3. Mnasitrement procedure

The sinkage apparatus as shown in Fig.. 4 was installed on the experimental platform under the towing carriage.

The bodily sinkage was measared by two dif-ferential transformers ( D . T . F . ) , which consists of a core-pin and a coW, these cofls were fastened 'two beam girders which were placed at 'interval

of Lpp, and the core-pins in the co'il were verti-cally mounted on the foreword and afterward perpendicular of the mode! ship. The models were not allowed the horizontal motion which would bring forth an error in the sinkage ; that is, the towing rod allowed the model to heave freely but prevented fore-and-aft motion, and the course setting poles checked yawing motion. Then the .sinkage was shown by recording on a Direct

Fig. 4 Testing model A 3.

12 A. Y A M A G U C H I , K. H O N D A , S. M A T S U K I and K. H A R A Recording Oscillograph the variation of voltage

of D. T. F. corresponding to the sinkage of mo-dels. I t was so easy that the records were ac-curately read to the tenth of 1 mm.

Previous to the testsy the records on the oscil-lograph paper were calibrated according to the change of the vertical position of core- pins. After the propeller revolution of model ships was brou-ght up to the proper value corresponding to the speed of the actual ship, the towing carriage was accelerated up to the constant speed. Once equi-brium was established, the records of the .sinkage were started. These records gave the sinkage at F. p. and A. P. where the core-pins were put on the model.

m . TEST RESULTS A N D CONSIDERATION From a seires of sinkage-tests of models in the shallow water tank, the following results were cleared. That is;

a ) When a f u l l scale ship was underway i n a straight and shallow water passage both under the f u l l load condition and at a speed within the commercial speed, the ginkage of the bow was more further than thai of the stern, and even i f the water depth became extremely shallow, such a tendency as trim by the head did not change and yet the excessive sinkage of the stern, what is called "SQUAT", did not occur. Consequently, in case of navigating in an even keel in the

14 A. Y A M A G U C H I , K. H O N D A S. M A T S U K I and K. H A R A Model : M Üond. : i ? u l l T r i m : 0 •}= r p n : V a r . W/B : 15.02 1 . 0 0 0 . 2 5 0 . 5 0 3 1 n k a « e / L p p

Fig. 9 Stern sinkage in the restricted channel 2 Lpp wid

0 , 7 5

b ) The initial trim had hardly affected the mean sinkage at midship except for the change of trim underway, which went down i n proportion to the initial t r i m set'by the stern. It was ob-served that these changes-of-trira underway were reduced in proportion to the initial t r i m set the more by the stern and at the same time had hardly dmerged in case of running at the initial t r i m by the stern 1^0^ of Lpp, as shown i n Fig. 10. Moreover, such a tendency had not been af-fected too much for the water depth. However, in case of the ballast condition at initial t r i m by

the stern, a contrary tendency emerged that the sinkage of the stern was further than that of the bow at the water depth in H / d = 2.0 as shown i n Fig. 11, though they were scarcely influenced at the water depth in H / d = 3 . 0 . I t was reason-able that the changes-of-trim between the f u l l load condhion and the ballast condition under load condition as well as changes of the sinkage of two models, A type and B, should have resuhed f r o m the changes of the submerged part of the hull. (See Fig. 12)

•16 A. VAMAÖUCHi, K. HÖNDA, S. MAtSUKl and K. H A M

del ! A3, 33 aoni i F u l l H/rt : 1.2 W/3 : 4.34 rpa : Var. ï o r » Aft 0.25 0.75, 1.25 • 1

X

Fig. 12 Comparition of sinkage between model A 3 and B 3.

c ) The empirical sinkage curves obtained f r o m our test results had shown the same tendency as the computed sinkage curves by Kreitner's me-thod. The empirical sinkage may be rather larger than the computed sinkage. And differences bet-ween the ineasured and computed curves of sin-kage may depend not only upon the increase and distribution of flow around the model ships but upon the influence of charmel boundaries. From the empiiical results of the sinkage. tests on model ships, if'was deducted that the bodily sinkage in a narrow channel was mainly derived f r o m the ratio ofj-wetted midship-section area of the ship..

(As) to the normal cross-section area of channel

A ( A / A : . i s c a l l e d ' B L O C K A G E ) , ' b u t scarcely affected by the water depth. And besides, f r o m our empirical observation as reported in Appendix, it was regarded as a better appropriateness that the sinkage of a ship underway in the extremely restricted depth depended upon the increase in relative velocity of side water more than of bot-tom water around her.

d ) The sinkage of F. P. and A. P. of the model had been so much affected neither by the revolu-tion of model propeller as shown i n Fig. 16, nor by the vertical position of towing point jointed

with the model as shown i n Fig. 17, and at the same time the change-of-trim on model without propeller made much differences neither i n fore-ward movement nor i n afterfore-ward. From these facts, it has been known that the change-of-trim on model may be mainly affected by the move-ment of flow, a hull shape of ship, around a model.

e ) A "small scale test could not make plain any scale effect, which was most important for predicting the sinkage of a ship. As the irre-gular dat3. cótiid not estimated any appropriately the change-of-trim at a certain ship's speeds, the sinkage of the bow could not be determined by the addition of the change-of-trim td the esti-mated mean sinkage. On that account, the mag-nitude of the bow sinkage of an actual ship underway at' commerjcial speed i n the shallow water of unlimited width was estimated by plot-ting the e'mplrical data of three similar A-type¬ models on graph. I n an extremely shallow water of Lpp^width and 1.1-1.3 draft depth, the allow-able operating maximum speed, which would be kept f r o m the risk of striking the bottom, was estimated as shown in F i g . 19 or on Table 2. For example, the limited speed for a very large

20 H/d 1.2 1.0 .05 A. Y A M A G U C H I , K. H O N D A , S. M A T S U K I and K. H A R A ' .06 U/Ji ! 25 .07 r . -Irin : 0 JS

Ship Bpeed (Knot) for 255i» tPP 3hlp 10 11 12 15 14

.09 .11 .12 Froude'a number

.13 .14

Fig. 19 Limited speed of very large vessel underway in the extremely shallow water.

.1?

Table 2 Sinkage of very large vessel underway i n the shallow water

Fn

Fore sinkage Mean sinkage Change of trim Fn H / d = 1.2 1.1 H / d = 1.2 1.1 H / d = 1.2 ' 1.1 0.09 0.175^ 0.195,q^ 0.14096 0.155^ 0.08096 0.080$^ 0.10 O.210 0.235 0.170 0,190 0.080 0.080 0.11 0.250 0.285 0.210 0.255 0.085 0.090 0.12 0.305 0.415 0.245 0.335 0.110 0.140 0.13 0.375 = 0.290

-

—

-

-

Note: sinkage expressed as a percentage of l p p

vessel such as D . W . 100,000 t tanker underway in the shallow water 1.1 times in draft would be about 12 knots. The limited speeds in Fig. 19 w i l l be about the same as that in the shallow water of unlimited width for the reason of lower speed phenomena.

Our test remained many unsolved problems in estimating the sinkage on any actual ship. The experimental resuhs of our test w i l l be compared favorably with the sinkage data which are obtained f r o m a full-scale test in the next program and w i l l also be made sure of i t

A C K N O W L E G D E M E N T

These tests, which were experimented in 1964 and 1965, were sponsored by The T h i r d Dist-inct Port Construction to The Transportation Ministry i n our

country-Acknowledgement was due to the Kawasaki Shipping Yard for the production of the test equipment, and " N . Y. K. Line" Shipping Com-pany for the assistance of the test. Special ack-nowledgment was also due to Prof. H - Sasajima to the Naval Architecture Department of the University of Osaka, Prof. M- Inui to the Naval Architecture Department of the University of Tokyo for advising of the test, and the following staff members to " N . Y. K. line" Shipping Com-pany for helping of the'experimental w o r k ; M r . A. Okawara, Mr.^T- N o j i r i , M r . T . Kado, M r . A. Tanuki, and M r . A . Kato.

A P P E N D I X

I n order to research the flow around ship's body, a series of tests were carried out with a test diagram as shown in F i g . 20.

Model Test on Sinkage. of Vessel Underway in Restricted Channel ₂₁ These tests were proceeded under the same

condition as the sinkage test by using A-type mödel of 1 ra long, and a small tank of 16 m long, 60"cm wide and 30 cm deep, wliere the movement of flow around her' was observed' through two transparent boards put both on side 'and at the

Touing carriage

bottom of tank. In the Water of observable parts of the tank we floated many granules which were adjusted' to become the same specific gravity as-that of water in the tank by properly mixing, two different liquids of Chlorobenzene (C„Hr,Cl, S. G. = 1.1064 at20°C) and .Xylene (C„H.i(CHi,)a,

]

Fig. 20 The flow-measuring

equipment-& G. = 0.8642 at 20''C).

•When the model ships were moved at a given speed with a towing carriage, these many floating granules were also moved corresponding to the flow around them, and these movements were

re-corded with two 8 mm-movie-cameras from two directions of the bottom and the side of tank, the movie film was enlarged with a projector at every frame and traced along the Soci" of these giranules.

Modol ; Al Oond : F u l l 1.1 fpa- : 0 Trim _{•! Pn ! .063}

J_ ,

^—

^

22 A. Y A M A G U C H I , K. HONDA, Fig. 21 was an example of distribution charts of flow showing the loci of flow while a model moved 10 cm ahead, then we recognized that the flow velocity under the ship was generally smaller than that along the side of the ship.

REFERENCES

1 ) R. S. Garthune, B. Rosenberg, D . Caliero and C. R- Olsin : "The performance of model ships in restricted channels i n relation to the design of a ship canal". Taylor Model Basin report 601, 1948.

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

2 ) J. Kreitner. : "Über den Schiffswiderstand auf BeschrSnktem Wasser", J. S. T . G., 1952.

3 ) M . Kinoshita. : "On the restricted water effect on ship resistance", S. N . A. J. No. 76. 1954.

4 ) H . E. Saunders. : "Hydrodynamics i n •ship design", Vol. 2, S. N . A . & M - E., 1957.

5 ) A . Yazaki and E. Kuramochi. : "Tank ex-periments on the effect of the shallow water upon the resistance and propulsion of a super-tanker", Monthly report of Transportation Technical Re-search Institute, V o l . 9, No. 8, 1957.