ARCHIEF
This paper deals with analyses of some speed trial results of actual large tankers, based on model experi-ments in a towing tank and a wind tunnel in order to investigate the increase of hull resistance due to shallow water effect..
MODEL EXPERIMENTS IN i TOWiNG TANL
The increase of hull resistance due to shallow water effect, considered qualitatively, may be classified as
follows:
The sea bottom being close to the bottom of a ship, the relative velocity of the water along the ship hull is increased, and eventually, the frictional resistance is incrásed.
The wave-making resistance is increased as the chUow water affects wave-making phenomenon.
According to theoretical investigations already
pub-Ijshed12'3) it is considered sufficient to treat only the increase of frictional resistance, ignoring the shallow water effect upon wave-making resistance in such low values of Froude number as are under consideration. In order to confirm this assumption, nodel expeninents of shallow water were entrusted to the Experiment Tank of Tokyo University. A model of 2.15 ni in L,, was used, that was one-hundredth of an actual 47,000 T tanker. The experiments were carried out at water
Gol
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APPENDIX Reeearch, Vol. 9, No. 1, June 1965.
47) SVANSSON. A. and Nyanao, L: Mätinstrument för
Hays-APPENDIX i
EFFECT OF SHALLOW WATER UPON THE RESISTANCE OF LARGE TANKERS
by M. KINoswm (Hitachi Shipbuß4ing & E'zgmeenng Co., Ltd.) and S. Suno
Lab. y. Scheepsbouwkunde
TecIrnkche Hogeschool
Deift
:
itrilnunar, Swedish ShipbUilding Research F"i'n, cpon No 43, 1965.
depths of 2.4 ni (the natural depth of the towing tank),
0.4m and O.3m
(corrpondingto4omand30mre-spectively of the actual trials).
The results of the expeiànents were analyzed eter
Th. Huics' method, eimatiog the icrement of
fric-tìin4 resict1w at the OE4m and 0.3 'n depths by an
experimental formula given by TanJgUChÍ and Tamura4)..
The analytical results are shown in Fig. I, and wave-making resistance coefficient deduced finni Fig. i &e shown in Fig 2. The wave-making resistance coeffi-cients at the three different depths of water, comred with one another, show no difference at all up to F= 0.20. Fig. 2 shows additionally wave-making resistance coefficients obtained from the results ofOiJiiwAymodel tt entrusted to the Mejiro Model Basin of the Ship Re-search Institute, the Ministry of Transportation, using a larger model of 6.5 ni.
These quite agree with the results of the experiments at Tokyo University. According to the results of all these experiments, it has been verified that the fore-going assumption is quite right
ANALYSIS OF TRIAL RESULTS CF ACTUAL T»cus
Trial results of many large tankers built by Hitachi Shipbuilding & Engineering Co., Ltd. were analyzed
0
I'J 1 13 14 1 16 i 18 1.9 ao Zt ¿2 sI Os
Re.VL/u(16.3 C) Fig. 1. Total resistance coefficient.
"E[
-sl
D
-114 PERFORMMJCE SESSION
5
LA
Ø3 B Q4 05
0.6
Relative Depth, YLAI
Fig. 3. gate of increaseof frictional resistance.
0.00 0.00 0002 0001
T'
0001 ODO/
after Dr. Hughes' method, and the results gave an aver-age value of 0.0002 for roughness allowance of actual ship hull AC,. So, when the shallow water effect is to
be considered, the average AC, value 0.0002 is de-duced from the frictional resistance coefficient of the actual ship, derived from its trial results, and the fric-tional resistance coefficient of an ideal smooth hull is determined. The difference between the frictional
re-sistance coefficient of a smooth hull C', and the fric-tional resistance coefficient calculated by Dr. Hughes'
method C, may be considered as the increment of
frictional resistance due to shallowwater effect.
Thus, by expressing the ratio of the square root of mid-ship area to the depth of
water as 4A/H, called
"relative depth of water", a relation between the rate of increase of frictional resistance
tx=(C',C,)/C, and
the relative depth of water is obtained as shown inFig. 3. Kinoshita, one of the authors, developed an uhdermentioned formula to predict the critical depth of water where the shallow water effect appears in hull resistance.
H/D 30V/fiL (H:
water depth, D: draught of ship)a
120
(%)-I9I(,-o.f.,es (V4I-O.3a)
o
.Io
023
This formula gives values of 62 m for actual tankers A and B, and 47 m for actual tankers L and M, which approximately agree with water depths of trial courses in which their speed trials were conducted.
Accordingly, the results of the tankers A, B, L and M
show that f/H is 0.32 for the
critical depth of waterabove mentioned..
Taking this pint as the origin, a curve of the second order was determined by the method ofleast squares.
cr(%)= 191(.fA/H._O.32)2+
16.6(47HO.32)
SHALLOW WATER EFFECT ON SmpsWITH LARGE Bui..ous Bow
The foregoing analysis is concerned only with ships with ordinary- bw form. In the case of a 100,000 T tanker fitted wiÑIì a large bulbous bow, however, a con-siderably large AC, value was given by the same
analyz-ing method as in the case of the ordinary bow formi Namely, deducting 0.0002 as roughness allowance AC, from the frictional resistance coefficient of the tanker derived from the trial results, the frictional resistance
coefficient of smooth hull is got, and comparing this co-efficient with Dr. Hughes' frictional resistance coeffi-cient of smooth fiat plate, the form factor "K" would be apparently 0.51.
"K" obtained from a resistance test of a model of the tanker in a towing tank is 0.36, and accordingly, the rate of increase of frictional resistance becomes 11%
-When the shallow water effect on this tanker is
con-sidered, the rate of increase of
frictional resistanceshould become 7.8% by the new formula, and thus, the difference 3.2% remains unclarjfied.
However, as described in another contribution to this conference5), it is concluded that, by analyzing resist-ance test results of a pair of models, the form resistresist-ance decreases by adopting a large bulbous bow as follows:
K=0.36 for the bulbous bow ship
i
i
OL
Hsa4Qm at the Medel Basin H0.40m H0.30m Retilts -i--Mejio I--.,I 021and K=0.40 for the ordinary bow ship,
while the two have quite similar lines except the bow form.
Now, if the increase of 7.8% of frictional resistance due to shallow water effect is applied to the ordinary bow ship with K=0.40,
C,= (1+ O.078)(1 + O. 40)CF,= 1.51 C,, and thus, this coincides with K=0.51 above mentioned. Therefore, it may be assumed that the flow-smoothing effect of the bulbous bow was lost due to the shallow
water effect, as the three dimentional flow was
re-stricted. The 100,000 T tanker had an additional speed trial on a deep sea, and 4C, value obtained from this trial was about 0.0002. Thus, it was confirmed that the result of C, =1.51 C,, was due to the shallow water effect, which will be discussed in the next section.
MODEL EXPERIMENTS IN A WIND TUNNEL
In order to clarify the problem mentio'-d abrve, the form factor "K" was measured in a large wind tunnel of Osaka University. The resistance at issue was meas-wed by the usual method employed in the wind tunnel
tesi, and an image model of nr 1r
hull corre-sponding to each of the bulbous and o- bow formsof the 100,000 T tanker in questk:.. . fixed in the wind passage of the wind tunnel by strings. Also a shallow water test was conducted by installing in the
wind passage two fixed plates, which were likened to the sea bottom.
Here, a corresponding ratio of water depth to ship draught was about 3.4, approximat1y equal to that of the actual trial runs under consideration.
Results obtained from the wind tunnel tests are
shown in Fig. 4 auid summarized in the following table.
Condition N Kind.ofBow i Bulbous De.p 2 Ordinary 3 Bulbous Shallow 4 Ordinary UK in Wind Tunnel 0.36 0.49 0.62 0.58
"K" n
Towing Tan& 0.36 0.40 APPENDIXus
in Trial 0.51 aoAPPENDIX II
SCALE EFFECT EXPERIMENT ON TANKER MODELS
by K. Yoxoo (Ship Research Ins:.)
'n: rote deals with the scale effect experiment on 276 m tànker and the other for a 249 w tanker. two families of tanker models. One. of them is for a
8U CUS , peep ordinary, beep BUlbOUS,shcllow ordinary, shallow ¿.5 2.5 3.5 Re x
Fig. 4. (1+K) Obtained from the wind tunnel test. 'K" value in the case of the deep water shows rather high value for the ordinary bow, but the results coincide approximately with the results of the resistance tests in
the towing tank.
In regard to the shallow water effect on the bulbous bow form and the ordinary bow form, the results from the wind tunnel tests and the actual trial runs are some-what aifferent from one another. However, the rate of increase in the case of the ordinary bow form in the wind tunnel test appears to be approximately equal to that obtained by the above-mentioned new formula, and the scattered values seen in the above table may be
allowed as experimental errors.
From these investigations, it is fairly reasonable to assume that the advantage of the bulbous bow owes a great dea1 to the reduction of the form resistance, how-ever, this advantage could not be expected when in the shallow ..ater.
R.EFERENCES
Sc; LICmTING. Schiffwiderstand auf beschränkter
Wasser-ties. JS.T.G., 1934.
W '.rBLL" Wellenwiderstand auf beschränktem Wasser. J. .G 1938.
L'.. ethers: Shallow Water Effect on Wave-making
Re
:,
Comparison of Calculated and Measured Resiace. Jour, of S.N.A. of Japan, 1956.T .."ruzIu and TAMURA: Effect of Tank Boundary on Mode1 Resistance. Jour. of S.N.A. of West Japan, 1955.
KiNosHrrA,OXADAand Txoi: Effect of a Bulbous Bow
upon the Resistance of Ships with Small L/B and Large
