Speed and power prediction techniques for high block ships applied in Nagasaki Experimental Tank

February 1976

MITSUBISHI HEAVY INDUSTRIES, LTD.

ARCHIEF

Tech

'

Ho

A

MITSUBISHI TECHNICAL BULLETIN

No. 103'

Speed and Power Prediction Techniques for

Applied in Nagasaki Experimental Tank

Kinya Tamura*

The model-ship correlarion method applied in the Nagasaki Experimental Tank, MHI and its historical background are described. The method, which belongs to the category of theoretical methods, has been used for speed and power prediction of various kinds of ships during these twenty years.

The difficulty in power prediction caused by the rapid expansion in size and block coefficient has been overcome by the introduc-tion of a three-dimensional extrapolaintroduc-tion method in place of the two-dimensional one, without making any serious misleading pre-dic tion.

For the current high block ships, it is essential to distinguish the type of flow pattern, around the stern of the model since two kinds of flow pattern exist. The method used to distinguish the flow in model and its influence on model-ship correlation are

dis-cussed.

1. Introduction

Speed and power prediction is one of the most impor-tant aims of model tests. Every model basin has made constant efforts towards the development of its own model-ship correlation method in order to improve the accuracy of prediction for varying size and type of ships. At the same time I.T.T.C. Performance Committee has made a study on evaluation and standardization of these methods.

Model-ship correlation methods in current use are di-vided into two groups.

(1> Correlation is applied to total, measurable values such

as shaft horsepower and r.p.m. (or simply, the scale effect of wake not being taken into account).

(2) Correlation is applied to the basic components such as resistance and self-propulsion factors (or simply, the scale effect of wake being taken into account).

The former is in accordance with the I.T.T.C. 1960

method and ¡s represented by (1 + x) & k2 method, the cor-relation data of which were reported by Moor0 to 13th I.T.T.C. in 1972. The latter ¡s represented by the method proposed by Lindgren(2) which was reported to the same conference and regarded as a reasonable compromise of

theoretical methods.

No matter which correlation method is used, the speed and power of a ship will be predicted with satisfactory accuracy if the prediction is made based on the properly chosen correlation factors. Therefore it is not sufficient to appraise a method by the fact that the prediction for a particular ship gives good coincidence with the trial results; appraisal of the method should be based on the ability to estimate the proper correlation factors for a ship which ¡s different in size or type from those in hand. In the theoretical methods selection of correlation factors has been made in consideration of their physical meaning. On

The main part of the paper was presented at the First Ship Technology and Research (STAR) Symposium, Washington DC., August 26 29, 1975.

the other hand in the (1 + x) & k2 method the prediction should be based on the accumulation of correlation data

antI analysis of the data is most important to make a

reliable prediction.

lt

is not the author's intention, however, to discuss

further the selection of correlation method, since this is the task of the I.T.T.C. Performance Committee.

In the present report the author intends firstly to show how Nagasaki Experimental Tank, MHI has developed its own model-ship correlation method for speed and power prediction of various kinds of ships and how it has coped with the remarkable increase in size and block coefficient of ships during these twenty years, and secondly to present a common base for further improvements of model-ship correlation method and problems in treating high block

sh l PS.

2. Model-Ship Correlation Method Developed in Nagasaki Experimental Tank

2,1 Historical background

The trend of increase in size and block coefficient of tankers started in about 1955 and it has been accelerat.d since about 1964. The time of delivery of typical tankers and time of corresponding model tests made in Nagasaki Experimental Tank are compared in Fig. 1. In the figure it is shown clearly that prediction of speed and power of large tankers up to 200,000 DWT had to be made from the correlation data derived from those smaller than 100,000 DWT without any time allowance to confirm the predic-tion results. As a matter of fact this was done without causing any serious troubles by making use of the

model-ship correlation method to be described in the following. Nagasaki Experimental Tank started the tank tests as early as 1908. In those days models of 4- 5 m in length

were used as a standard. With the completion of the present larger tank in 1944 it was intended to use 6 - 7 m models, but the operation of the tank was postponed about ten years because of the destruction of tank facilities by the 2nd World War. In the mean time thorough examinations were made on the method of analyzing model test results and accordingly the method of model.ship correlation. As a result a new practice was introduced for them which has been applied to the tank tests resumed in 1953. A change to the modern practice was thus accomplished without trouble though we have the longest history of tank testing in Japan.

The alteration of the practice was facilitated by the fol-lowing changes in model testing technique and ship con-struction method.

Artificial turbulence stimulator was introduced at the time in order to ensure the flow over the models would be fully turbulent. This certainly reduced the usefulness of former model test results accumulated in our tank.

Electric welding was introduced so rapidly to ship-building industry in Japan after the 2nd World War that the amount of welding applied to shell construction was increased successively even in a series of sister ships. Thus it was necessary to make speed and power predic-tions for different structural roughness of hull from the

same model test results.

The influence of (2) on power prediction method was more essential. The formal tank DHP & N method based on the Froude's correlation line could not take into account the difference of structural roughness, and a new method was required having more flexibility with scientific basis.

The model-ship correlation method of Nagasaki Experi-mental Tank was developed under these circumstances and its main system was completed in about 1955 in com-bination with the method of tank tests and their analysis.

The author would like to emphasize the fact that the method was not devised at one time but built up gradually through our experience in power predictions.

2.2 Outline of the model-ship correlation method in Nagasaki Experimental Tank

The basic concepts for analysis of ship trial results and power prediction are given in Figs. 2 & 3 respectively. This is based on the assumption that the influence of propeller load on self-propulsion factors can be neglected. The propeller open water characteristics for trial analysis and power prediction, correspond to. propeller-particulars of a ship. The trial results for analysis are to be corrected to the state of no wind and no tide. The correction for wave

and swell is also desirable.

Two correlation factors both for viscous resistance and for wake fraction are applied as follows:

Where is the total resistance coefficient of a ship de-rived from trial analysis and C0 is that dede-rived from the model. C0 is preferably calculated by making use of a three dimensional extrapolation concept, i.e. adoption of form factor, and it is indispensable for high block ships.

No matter what kind of model-ship correlation line is

used there is no difference in practical application of our method, provided the same correlation line is adopted for both calculations of ship trial analysis and speed and power prediction and thus obtained .ACf and e are used.

The explanations of our basic concept and how we developed the method to the present state are described in the following sections.

2.3 Basic requirements for a model-ship correlation method

In the first stage of tank testing any means for predict-ing ship's speed and power from model tests was regarded

as a model-ship correlation. In the course of

develop-ment, however, the scope of model-ship correlation has been confined owing to the basic assumptions in the

Model Test Results

[Cr] or[Cw&K]

[t,WM, ?r]

Ship Trial Results Vt, SHP, N

Propeller Open-Water Characteristics

for Ship

Fig. 2 Basic concept of ship trial analysis

950 960 1970

LCf = Cjç

-

C0

(1)

Fig. 1 Time of model test and delivery of ships e

_{= (1 WM)/(1 - W)}

(2)

o--.Model Test ---Deüvery of Ship 400 300 -C (f) o 200 w -o o w o loO

V

Model-Ship Correlation Factors Cf=

C0

e = Il - WMI/(1 - wl

Model Ship Correlation Factors %Cf, ej Resistance Test

[Cr] or [C&K]

[t,_{WM, tr]} Power & N for Ship Self-propulsion Test Propeller Open-Water Characteristics for Model

V

Propeller Open-Water Characteristics for Ship

separation of resistance components, scale effect of self-propulsion factors and so forth.

This trend should be continued in future and the model-ship correlation method in current use should be improved further. In view of such developments the basic require-ments for a correlation method shall be stated as follows. To be flexible for future development of technology and model test techniques.

To have wide applicability for many kinds of ships. To be applicable to power prediction for ships in a seaway, with fouling bottom and propeller, and for cavitating propellers.

To be applicable to ships with a propulsor different from ordinary screw propellers.

To be simple and accurate enough for the practical

purposes.

The flexibility mentioned in (1) implies that powering can be predicted without repeating the model tests, even when the correlation line or the analysis method of the

model test is revised.

In order to fulfill these requirements it seems to be reasonable to constitute a correlation system comprising the three major components, viz, resistance coefficients, self-propulsion factors, and propeller open-water charac-teristics. Besides, it should be kept in mind that the corre-lation method itself is less affected by the alteration of

model test procedure or analysis method. lt is also desir-able that correlation factors n this system should provide physical meanings as clear as possible for the sake of wider appljcation for different size and type of ships and for different boundary conditions.

In this direction our model-ship correlation method was explored.

2.4 Development of the correlation method

Fig. 3 Basic concept of speed and power prediction

Usually three kinds of data, i.e. speed, horsepower and r.p.m. are measured at the speed trial of a ship. Thus the correlation between model and ship is reduced to the selec-tion of two independent factors whatever correlation method is adopted, It is natural, therefore, to apply these two factors to the elements which have dominant effects in correlating model and ship data. The effects of other elements are to be assumed in any way.

In the beginning an attempt was made to correlate the r.p.m. and relative rotative efficiency 77,. between model and ship, since the accuracy of 'tir was comparatively lower in those days than other self-propulsion factors in the model. It turned out, however, that such a method could not take the effect of different rate of welding of shell construction into account and the correlation factors were changed over to viscous resistance and wake fraction.

The necessity to correct the scale effect of wake at power prediction of a ship was already pointed out by R. H. Froude at the initiation of his propulsion tests. In doing this in practice, however,

method of evaluation of propeller open-water charac-teristics for power prediction and trial analysis should be determined,

and scale effect of thrust deduction fraction t and relative rotative efficiency 'tir and

influence of propeller load on self-propulsion factors

should be assumed.

For the item (1) it was decided to evaluate the propel-ler open-water characteristics at standard Reynolds num-bers as explained in the next section.

For the item (2), the scale effects on t and 7lr were neglected.

For the item (3), the influence of propeller load also could be disregarded after careful examination on model.

At this time, however, almost all the models had rela-tively low block coefficient, therefore the influence of propeller load on self-propulsion factors for high block ships as current tankers has to be examined again, as is stated later.

Thus our model-ship correlation method was obtained, the outline of which is given in former section. The basic procedures of calculations for ship trial analysis and speed and power predictions are given in Tables i and 2 respec-tively.

The correction for added air resistance in these tables is applied to the difference of above water shape between model and ship in the state of no wind. The detailed description with data of correlation factors was reported already by Taniguchi. The Japan Towing Tank Com-mittee has adopted this as J.T.T.C. method.

and e can not be decided separately as some extent of correlation exists between them. But the effect of structural roughness will be corrected by modifying

as they are mainly concerned with ¿Cf. 2.5 Evaluation of open-water characteristics of

propellers

In our model-ship correlation method open-water characteristics of the propeller play an important role of coupling the resistance and the propulsive performance;

Table i Ship trial analysis

(2)N5 (rpm)

(1) V (kn) (3) SI/P (ps)

ship trial results (corrected for tidal currents and wind).

(4)DHP

DHP=SHP(stern

tube friction loss).

K

_75DHP

2p,i3D5

x 1/(No. of propellers),

n = N5/60.

77 _{7?rs = 7?rM} (from self-propulsion test).

KQO =KQ x m-s.

.1 read off from propeller open-water

char-acteristics through KQO (7). K7-(1G) ws

i w5=

,v5O.5l444x V5

ej or T t5 R

R0

¿NRa, LRa= difference

of air resistance between model and ship in no-wind condition.

C C5 = non-dimensional expression of total resistance _R0

-cts0 total resistance of ship derived from model test

(CtSO=CY+CfsO orCW+CfSQ(l+k). Cf

Cf= C5 -

Cr50 = ¿Rf/_vS2S.

self-propulsion factors are derived from resistance and propulsion test results by way of propeller open-water characteristics and power calculations are made coupling

the resistance and self-propulsion factors by propeller open-water characteristics as shown in Fig. 3. Here lies a major difference from the (1 + x) & k2 method in which propulsion tests are of primary importance. Evaluation of open-water characteristics has a direct influence on the model-ship correlation factors and their physical meaning. Careful examination was made therefore on this subject to build up our practice which shall be described in the following.

For analysis of self-propulsion factors we use the open-water test results obtained at nearly the same Reynolds number as those in the self-propulsion tests. Considerable scale effects are expected in generally lower revolutions of

a propeller, so the open-water characteristics should be

those corresponding to similar state of flow on the

propel-Table 2 Power calculation of ship

V5 (kn) ship speed (given).

vs i/i Froude's numbers, v5= 051444V5,

L = ship water line length.

v5L/v Reynolds' numbers at 15°C and sea water.

C-5o from correlation line.

CJ from model-ship correlation data analyzed on the same correlation line (4).

C0 = Ç + cf50 +

cf

or = C + CfSØ(1 +k) +

(Cr or C and k are derived from model

test).

total resistance.

R0

+ _{¿SRa, .Ra =} difference of air

re-sistance between model and ship in no-wind condition.

EHP(ps) R0v5/75,

effective horsepower.

t5

t = t

(from self-propulsion test). (11)7'

T= R

1 -

t5

from model ship correlation data. 1 - WM 1 - w5= e v

=v3(1 w5).

(15HJKT/J=

_vii

D = propeller diameter. read off from propeller open-water. characteristics through \[KT/J (15).

1

-"ills =

--

w5

Tirs = TìrM (from self-propulsion test). Q.P.C., _{?a =u?pTirs}

(21)D//P(ps) EHP/"la

(22)SHP (ps( DHP +(stern tube friction loss).

)23) N (rpm) N= 60.

?rs ?a calculated by (11),(14) andD, Ç0 Ri-0 R e w5

v,

1er blades. According to our practice open-water tests are carried out on a date near the self-propulsion tests with the revolutions corresponding to the rated r.p.m.

This is supported by the following facts obtained by us. Firstly, by applying this procedure in the analysis of

repeated self-propulsion tests, self-propulsion factors are less scattered and scarcely affected by water tempera-tureW. Secondly, the flow stateon a surface of propeller model differs little between open and behind (self-propel-led) condition as shown in Fig. 4, where the outer part shows the turbulent flow and the inner part shows laminar flow. There may be scarcely the effect to promote

turbu-lence on a surface of propeller model in behind condi-tion(6).

For power calculation and trial analysis ¡t would be best to use the open-water characteristics estimated for Reynold numbers of ship propellers and for their surface roughness. As this was impracticable however and needed further study, the propeller open-water characteristics at standard Reynolds numbers were adopted for practical

purpose.

Standard Reynolds number is defined as:

Re(K)=/v2+(0.7nnD)2=4.5x105

(3)

where C,7 is the chord length of propeller blade at 0.7R, r is the advance speed and D is the diameter of a propeller. The value of Re(K) was chosen in a zone where the scale effect of open-water characteristics decreases and especially the scale effect of the thrust constant can he

Suction side IBack)

Propeller open test RelKl= 322x105 slip = 0.533 Self propulsion test RelKl= 3.27x10S slip = 0.478 neglected.

In practice, therefore, two kinds of propeller open-water characteristics are needed, the one for power prediction and trial analysis and the other for the analysis of self.propul. sion tests. Thus power prediction and trial analysis can be made even in the case when model propellers are not geometrically (exactly) similar to the ship propellers by adjusting propeller open characteristics for a ship. This affords a reasonable basis for utilizing a stock propellers in propulsion tests.

For this sake we developed the correction procedure for propeller open-water characteristics experimentally due to the difference of boss ratio and blade thickness/chord length ratio(8).

3. Efforts to Improve the Accuracy of Correlation Factors In order to make reliable speed and power prediction for a ship it is necessary not only to improve the accuracy of model test but also to refine the ship trial results which are supplied for model-ship correlation analysis. Every kind of effort has to be made for this purpose in the whole field concerned, from making models to measurements at speed trial of the ships.

In the following the author explains several points to which Nagasaki Experimental Tank has paid special atten-tion for the improvement of accuracy.

3.1 Acquisition of speed trial data

Measurements of torque, r.p.m., wind speed and direc-tion relative to a ship for correladirec-tion use are carried out by

Pressure side IFace)

similar models), wave and wake measuring techniques and so on ¡n Nagasaki Experimental Tank.

4. Wide Applicability of the Method

One of the special features of the present method is wide applicability to many kinds of ships and boundary conditions. In this chapter its typical applications are stated except for high block ships which are described in detail in following chapters.

4.1 Application for multi-screw ships

Power prediction and trial analysis for multi-screw ships are carried out in the same manner as for single-screw ships, provided self-propulsion factors for each propeller are given except thrust deduction fraction t which is treated as a whole.

n the case of power prediction for triple or quadruple screw ships an operational guidance of main engines, i.e. ratio of r.p.m. or horsepower between inner and outer engines should be given at a related speed. Power and r.p.m. prediction to match the operational guidance is obtained by interpolation. The propeller for each shaft is easily designed

so as to match the design constraints.

A calculation method of appendage resistance of a multi-screw ship was proposed by Taniguchi taking its scale effect into consideration.

4.2 Application for high speed boats

The method is applicable to high speed boats the propel-lers of which are subject to thrust and torque breakdown due to cavitation. Introduction of two additional correla-tion factors, however, are necessary in order to obtain the

same C1 and e1 in the non-cavitating zone. They are ap-plied to the rate of breakdown of thrust and propeller

efficiency due to cavitation derived from cavitation tests on the model and those from trial analysis.

Effect of shaft inclination is of primary importance in evaluating open-water characteristics in cavitating as well as in non-cavitating zone. By simulation of this effect in model tests reasonable values of Cf and e1 are

ob-tain ed 21)

The method can be applied to power prediction of a hydrofoil boat as well(22). In this case not only the resist-ance of foil, strut and shaftings but also air resistresist-ance of main hull obtained by wind tunnel test are taken into calculation. The self-propulsion factors are derived by behind test.

4.3 Application for ships with propulsor other than screw propeller

The power prediction and trial analysis of a ship with a propulsor different from an ordinary screw propeller such as controllable pitch propeller, vertical axis propeller and ducted propeller are possible provided the open water characteristics and self-propulsion factors are given. An example of application for vertical axis propeller was already given by Taniguchi(23).

4.4 Speed and power prediction of ships under service ourselves on board in order to eliminate personnel and

instrumentation errors. A method of correction for wind and tidal effects on speed trial results has been prepared for practical uset9t10. Correction for relatively shorter waves is under investigation ), since they are of signifi-cance with the recent increase in size of ships.

On the other hand, the distance of approach run neces-sary to reach a constant speed during the run between the mile posts was examined carefully and the calculation method for it was given to shipyards as a guide(12). The shallow water effect was also examined. The draft of I.T.T.C. 1963 Trial Code was prepared by TaniguchiO3 making use of these results.

3.2 Improvement of tank facilities and testing technique Every model basin has been making efforts to improve the accuracy of model tests by development of the testing techniques and extension of the facilities. Among the improvements introduced in Nagasaki Experimental Tank which deserves special attention is the installation of an automatic speed regulation system for the towing

car-riage(14) as early as 1953, which made a great contribution to the improvement of measuring accuracy for high block

tankers. Measurement of model speeds against water instead of ground speed and development of electric oro-pulsion dynamometers in 1954 also served the elevation of reliability

3.3 Estimation of open-water characteristics of ship propellers

In order to provide correlation factors with clear physi-cal meanings, it is preferable to use the open-water charac-teristics estimated for Reynolds number of a ship propeller and for its surface roughness. This would become inevitable when one intends to apply the resUlts of thrust measure-ments on board to correlation analysis. Taniguchi per-formed this calculation of open-water characteristics and applied it to trial analysis(1516). It was reported that the dependence of and e on Reynolds number is de-creased and their scatters are also reduced a little in com-parison with the former results.

3.4 Study on blockage correction

Correlation factors are influenced by blockage effect when a model size is different as used to be in a tank. Usually we adjust a model size so as not to exceed the predetermined limit of blockage (midship area of a model! sectional area of a tank) for our tank. In the case of exceed-ing the limit a blockage correction is applied to resistance. The correction method has been explored by

our-selves17)(18)

3.5 Study on scale effects and the separation of resistance components

This is the most fundamental work for the development of a model-ship correlation method and it plays an impor-tant role in the application of a correlation method to high block ships(1920) as to be stated in chapter 5. Studies are still continued by the use of geosims (geometrically

Mean power increase or speed drop in a seaway is

derived from power prediction based on the thrust or the resistance as increased due to waves and winds. Influence on self-propulsion factors is disregarded as a first approxi-mation. Validity of such a treatment has been confirmed

by model tests in waves(24)(25).

The bottom fouling effect is taken into account by an increase of ¿Cf and e, the data of which are derived from the analysis of service performance of a ship(26). The effect of propeller fouling is also accounted by a modification of propeller open-water characteristics.

5. Application to High Block Ships 5.1 Adoption of form factor

The model-ship correlation method of Nagasaki Experi-mental Tank described in chapter 2 can be applied to high block ships. In the beginning the correlation factors ob-tained by a two-dimensional extrapolation method were applied to power prediction for tankers in the same way as for cargo ships. However, values of LXCf became sometimes negative for tankers with high block coefficient. A negative 1Cf is in contradiction to its physical sense and may cause some trouble in speed and power prediction, since it im-plies that the hull surface is smoother than a physically smooth surface. Such a defect was considered to be due to the following reasons.

Scale effects of self-propulsion factors except wake

were neglected.

Scale and roughness effects on propeller open-water

0.6 K) o X 0.2 o O -04 -0.6 _{05 0.6 0.7 0.8 09 .0 II} 0.8 K) o X o

r

Q) E 0.2 Q)

r

I

a -0.2

-0.4 ₀₅ 0.6 0.4 o N.B.

-.--- Mean value line Mean value ±stand deviption zone

characteristics of a ship were neglected.

Separation method of resistance components according Froude's assumption was not adequate.

Among these (1) and (2) did not seem to be a specific matter for high block ships, while (3) seemed to be impor-tant. In the mean time Hughes(27) pointed out the

neces-sity to introduce three-dimensional extrapolation, using a form factor to viscous resistance at the 7th I.T.T.C. (1954). The application of Hughes' method was tried shortly after the conference, as it has a tendency to dissolve the negative values of 7C'f.

Fig. 5 shows LXCf obtained by a two-dimensional extra-polation method with I.T.T.C. 1957 line, while Fig. 6 shows obtained by Hughes' method with Hughes' basic line and form factor. lt is clear that /.Cf in Fig. 6 are posi-tive and less dependent on Reynolds number, and therefore the three-dimensional extrapolation is more convenient for correlation purpose. These results were reported to I.T.T.C. Committee for Subject 2 & 4 (skin friction and turbulence stimulator) in 1959.

Methods of evaluating form factors are divided into two groups; the one, as proposed by Hughes, to derive them from resistance tests in low speeds, and the other to obtain them from analysis of resistance components of geosims (geometrically similar models). The former method was adopted as our practice since it is impractical to perform geosim tests. Resistance measurements in low speeds could be made with reasonable accuracy by virtue of the im-proved facilities and teting techniques such as the

auto-12 .3 .4 1.5 1.6

Reynolds' n Rn=VLWL/VX

I0-Fig. 5 Correction factor Cf (I.TT.C.) vs Reynolds number

.7 18 19 20 21 Standard deviation 22 23

..._

IStandard

deviation =

-- Mean value Line Mear value ±staridard

0.6 0.7 0.8 0.9 .0 1.1 .2 1.3 1.4 1.5 1.6 I? 18 9 20 2.1 22 ReynoLds no. RnKVLwL/V x l0

MIS 103 February 1976

matic speed regulator(14) and measurement of water speed. Its typical examples were already reported to 9th I .T.T.C.(28).

The three-dimensional extrapolation has thus been ap-plied to the powering of high block ships since as early as 1957. The validity of the method was confirmed later by the studies in resistance components for high block ships(19)(20)(29).

Recently extension of wave resistance theory to high block ships has been made by Baba and Takekuma° and application of the result to the estimation of form factor is under preparation.

5.2 An example of analyzed data

As stated in the beginning the 13th I.T.T.C. regarded the trial analysis method proposed by Lindgren(2) as a reasonable compromise and recommended that it should be used on all available data and the results should be re-ported. This was done in Nagasaki Experimental Tank on trial results of 54 ships. The proposed method is almost similar to ours except one point; the open-water

charac- 06- 04-o -0.2 0.15 OE IO 0.05 -0.05 .0 0.9 0.8 0.5

S--- Fall Loaded Condt,on

Light Loaded COndiOOn

.5

teristics of ship propellers are estimated from the open-water test results at the standard Reynolds number by the use of Aucher's formula. The equivalent sand roughness K is assumed to 3Op according to Taniguchi & Sasajima'

Viscous resistance is estimated by the use of I.T.T.C. 1957 line and form factor.

The correlation factors are expressed as follows. For

viscous resistance

C = C + C'f l.T.T.c. (1 + k) + C'f (4) For wake fraction

e1 [Eq. (2)] or .w= WM - Ws (5)

Trial data used in the analysis cover cargo ships with comparatively low block coefficient as well as high block ships for examination of applicability of the method.

As shown in Fig. 7 Cf are almost independent of Reynolds number and influence of size and type of ships is hardly noticed. On the other hand e or Lw are, as shown in Fig. 8, somewhat dependent on Reynolds number and

Reynolds No.

Fig. 8 Correlation factor on wake fraction (Method by Lindgren)

2.0 25 l0

Y

05 1.0 IS 20 25cl 0'

Reynolds No.

t. o a) 09 +0,20 -0,20 -0.6 -0.4 -0.2 0 .0.2 +0.4 +0.6 S LdCt ) 03

Fig. 10 Variotion of & w due to the Change of SHP

&N

e1 are relatively small (.w large) in the lightly loaded condi-tion. Further a definite trend of increase in e1 (or decrease in w) can be seen with increase of speed for each ship. The reasons for this are not clear as yet, but they are con-sidered to be shortage of distance of approach run in lower speeds, scale effects on propeller open-water charac-teristics and self-propulsion factors and so on.

Fig. 9 shows the correlation between and e1 or LCf and w respectively. A certain trend of increase in e1 (or decrease in iw) with increase of ¿Cf is often

ob-0.8 o FuU Load [4000000WT 0I5 1230,0000WT

\

150000DWT +00

\\\\\

o:5 -0.05-0.2 0.4 0.6 ¿lCq alo3

Fig. 9 Correlation between L Cfand e, w

Tanker 30. 000 BuLk Carrier --FuLl LOad O ---Tr,aL Load + 0.10 + 0.05 -0.05 0.8 0 0.2 N0 x 1.00 SHPO x 0.94 0.4 0.6 ,Cq X IO 0.8

served, but it is unclear in the present results.

The relation between Slip, N and /2Cf, Aw is examined for following high block ships such as 30, 150, 230 and 400 kDW tonners respectively. Fig. 10 shows the displacements of ¿Cf and zw caused by a change of ±6% in SI-IP and

±2.5% in N for above ships. The correlation between

and w obtained for variation of N with constant SHP is somewhat similar to the tendency of ACf and w in Fig. 9. Scattered zone of LCf and /w in Fig. 9 is almost enclosed by a quadrangle formed by the following apexes, when SHP0 and N0 are predicted by the middle

value of scattered ¿IC'J- and w for a certain ship. N0 x 1.025 N0 x 1.00 N0 x 0.975

SHP() x 1.06 SHP0 x 1.06 SHP0 x 0.94

This may show a range of causable error of power predic-tion. Of course it is still unknown whether Cf and ¿w of 400 kDW tonners are included within the same range as others until the trial results are obtained. A larger dis-placement of Cf for 30 kDW tonners will be due to larger C), value at the design speed which is comparatively higher for this ship.

6. Problems for High Block Ships

6.1 Two kinds of flow patterns around stern

One of the most serious problems for model-ship correla-tion of high block ships is the unstable phenomenon

in self-propulsion test.

This was pointed Out first by

Watanabe(3233) in Nagasaki Experimental Tank. Figs. 11 and 12 show an example of it. Thrust, torque and revolu-tions measured in self-propulsion test are expressed in

non-MTB 103 February 1976 0.04 70 r> o 1 0.02 Io 0.9 06 05 0.4 I? 03 0.2 0. I o 60 r> 003 002 001 o loo 0 25 0190 0115

Fig. 11 Results of self-propulsion test (Model-A)

,604 0200 0225 4.9 t) 4.8 0.145 0.I40 0.135 0.130 0.125 i .0 a, 0.5 2 c) 10 -o (0 0.5 o O l'i 5.1 5.0 4.7 4.6 1.0 os o (0 u-0.5 1.0 005 004 003 0.02 o EXP No.604 u

"

.

.'

"I'll'

11111I 1h

1hJI

j

Il

II

.15

jeIIIII

6 o 10.0 80 0.03 0.02 00' ₀₁₀ ?)m= .649 rn/S Thsr9972 I/S time Is

m- time

Fig. 13 Records of thrust, torque and side-force (Model-A)

0.125 T:5.095kQ 7=4.635kg Q-01443 kg.m QrO.1329kg.m 0I5 0175 0.20 0.225 Zr/rIE

Fig. 14 Result of self-propulsion test (Model-D)

WM in 65% load and the one in full load are named F type and that giving higher wM ¡n 65% load is named s-type. Thus the existence of two kinds of flow pattern causes a serious problem in using model test results of high block

°

VP

604No. o

AGF..,

-O O

t

p 0 o O fie No604 0.100 0125 0150 0.175 0200 0.225 u/J

Fig. 12 Self-propulsion factors (Model-A)

dimensional forms in Fig. il, while self-propulsion factors analyzed for each measured data are given in Fig. 12. lt is evident that apparently scattering data in Fig. 11 turn out to be two kinds of wake fraction in Fig. 12. This implies the existence of two kinds of rather stable flow around the stern of a model.

The two kinds of flow appear even in a single run of self-propulsion test. Fig. 13 shows the record of thrust, torque and side forces at fore and aft guide of the model and, when the thrust and torque are larger, the side force devel-opes to the starbord side in the aft guide with a clockwise rotating propeller. The direction of side force is reversed by a counter-clockwise rotating propeller.

Figs. 14 and 15 show another example, where the large difference of thrust and torque which is far beyond the error of measurements ¡s observed for the whole speed

range of test.

Existence of two kinds of flow around the stern was clearly demonstrated by the repeated self-propulsion tests on a tanker model M.1592 of Nagasaki Experimental Tank. Fig. 16 shows wake fraction WM analyzed for each mea-sured data. Tow kinds of 5'M are observed in 65% load condition, while only one kind of WM is obtained in full load condition through the whole repeated tests. After studies on this phenomenon, the flow pattern giving lower

LO 0.9 07 j 0.6 05 0.3 + 0.2 0I 05

i

0.6

j

05 06 r 05 0.4 0.14 PoLL Load

Fig. 15 Self-propulsion factors (Model-D)

65% load

Test

No-0 No.2-No.5, No.7--Propeller position A

u No.1 -- --- do B

No.6 ---. do

B

0.6

2737

0.5

016 018 0.20 022

Fig. 16 Scattering of effective wake obtained from repeated self-propulsion test (M. 1592) SFC kg 0,19 1; 2 SF0 g

No.I} propeller portIon B re

propeller poOItIOn S

Fig. 17 Effect of propeller loading on effective wake

ships. Figs. 18 and 19 show wake fraction of high block ships in a series test. lt is hardly possible to make a reason-able explanation of the influence of fullness of after body on wake fraction without assuming existence of two kinds

of flow pattern.

A question then arises how to distinguish these flow pat-terns from each other. Fig. 17 shows an influence of propeller loading on wake fraction of M.1592 which covers so wide range as from zero thrust to model point of self-propulsion. In full load condition WM decreases gradually due to the increase of propeller load (F-type) while in 65%

i

0.60 050 0-70 0.60 0.50 L.p p II-Cpa)r ₂₆

Fig. 18 Relation between effective wake fraction (WM) and fullness of aft-body

65%Ì Load

W[t0.I8

I-o values of sú, connected by dotted lise Show the

occurence of unstabLe phenomenon 0--- B/d 2.76

O---B/d 3.06

1753

Fig. 19 Relation between effective wake fraction (%tM) and fullness of aft-body

load condition two kinds of WM exist. The one decreases in the same manner as in full load and is classified as

F-type flow. The other changes little due to propeller load and is classified to S-type flow. The variation of _'M F-type flow with propeller load almost coincides with that of nominal wake calculated by taking the effect of

propel-ler suction on wake into consideration(36). Therefore F-type may be regarded as a normal type flow while S-type seems to involve peculiar phenomena. The flow type can be distinguished in this way. lt is now a practice in Nagasaki Experimental Tank to carry out propeller load variation tests as a part of self-propulsion tests at a certain speed for all the conditions to be tested.

In both flow patterns the rate of change of WM decreases and tends to be a constant value at a larger propeller load. Thus the power prediction method given in Table 2 can be

8 t7p o o 8_O=0._ o0 O o rl o o o

-

o o D O

rS..--

o 65%Load /J'io,2o

I

-

to 014 0.6 018 0.20 022 Full. load 0.10 0. I 25 015 0.175 020 0.225 0.80 0.60 0.70 I-pp ICpa)0 -j 060 070 0.80

applied to high block ships in the same manner as to cargo ships with comparatively low block coefficient, provided the self-propulsion test is carried out at considerably higher propeller load. The ship point of self-propulsion tests in Nagasaki Experimental Tank is expressed by in Fig. 17, which corresponds approximately to

LC0.2

x103 for I.T.T.C. 1957 line.

6.2 Consideration on selecting the correlation factor on wake for S-type flow

lt is not yet clear whether the existence of two kinds of flow pattern around stern is a problem peculiar to models. Further attention must be paid to trial results of high block ships. At present, however, the flow pattern of ships may be assumed to be of F-type.

According to our experience, most of the models of 6 -7 m in length with moderate shape of stern proved to be of F-type flow in full load. The correlation factors given ¡n Figs. 7 through 9 are considered to be those for F-type, since speed trials of the tankers included were mainly car-ried out in full load. On the other hand in ballast load the flow pattern more likely tends to be S-type. Probability of S-type in full load condition will increase with increase in fullness of ships and this is more liable for smaller models. lt is most important therefore to find a method of selecting correlation factors for S-type flow.

The self-propulsion test results of geosims of Niizuru-Maru, which were carried out under SR 107 project(29) for the study of separation of resistance components, show that the flow type of 4 m model is S in both full and ballast load while that of 8 m and 12 m models is F in full load and S in ballast load respectively. In Fig. 20 w derived from propeller load variation tests on an 8 m model is com-pared with the nominal wake w0 or Wye calculated by taking the effect of propeller suction on wake into account, where w0 is the volume mean of nominal wake and Wve S the weighted mean with a weight function similar to radial thrust distribution. Although wM in full load shows a trend to coincide with w

or w, WM in ballast load

Self- Propolsion Port

/.

Woe Valu,oe MeanWoe)

Wo

shows quite a different trend. On the other hand w ob-tained by trial analysis of the ship in full and ballast load shows comparatively good coincidence with each other as in Fig. 21. 08 FalL Load 3 3 0.7 ¡Balla:,LOad 0.6

-J

16 20

Fig. 21 Model-ship correlation of effective wake (Niizuru-Maru)

Similar results as those above are obtained for other pairs of ships and models. This may suggest a method of selecting the correlation factor on wake for S-type flow. Namely, the correlation between w5 and the nominal wake w1,0 or Wi,e, which is read off on the ship point of self-propulsion test in Fig. 20, may give better coincidence with each other than that between 't.' and wM irrespective

of the difference of flow type in

full and ballast load. However, further examination will be necessary for practi-cal use and the study on thrust deduction in S-type flow

should be pursued at the same time. 6.3 Other problems to be solved

It is desirable that correlation factors depend less on type, size, speed and load condition of a ship, thus the accuracy of prediction will be increased. For this purpose not only the study of unstable phenomenon in self-propul-sion tests should be pursued, but also correlation methods should be improved by taking the correction method of scale effect on resistance and selfpropulsion factors into account. This implies that correlation factors change in their character to a kind of coefficient for adjusting the scale effects presumed, or are refined to a higher order.

In doing this, however, the scatter of the correlation factors should be examined and an effort should he made to decrease

it. According to Taniguchi' scatter of the

present correlation data is caused firstly by speed trial data including measurement errors, length of approach run and effect of environmental conditions such as wind and waves, and secondly by model test results, especially ac-curacy of thrust deduction fraction, The recent trend of increase in size and fullness of ships tends to decrease the accuracy of those elements above which are indispensable for improvement of model-ship correlation. There is not a way at present but to make every possible effort to keep

0.6 _{Fall Load}

-

Ballast Load

-05

.0 Fall Load lOrs Ballast Load o

-0.4

_.1

0.3 _{N O Prop.lW, 00m, Oha,o0tq,jItjcS a, standard Reynaldo'} 00mb., a,.us,d 0 tat trial analysis

0.7 0,6

i

05 0,4 t, Foil Load Seif-P0puisi0rs Pant 02 0.4 0.6 0.8 C° I/9v202 lO 04 0 0.2 0.4 0.6 0.8 .0 C7OT/,V202

Fig. 20 Effect of propeller loading on effective and nominal wake (Niizuru-Maru)

Ballast Condition

or

0.6

the accuracy of speed trial and model test and to collect accurate correlation factors.

n model testing larger scale models are necessary since for a modern ULCC, model propeller size is considered to have reached a minimum in view of the accuracy both in experiments and manufacture. Artificial turbulence stimu-lation on propeller blades will also help to improve the ac-curacy of model tests.

With regard to full scale data it is highly desirable to the author to get comprehensive support among people concerned for making such accurate speed trials of a ULCC as to be applicable for improvement of correlation method and of accuracy of power prediction, though it is expensive and time consuming. For this purpose the increase in accu-racy of measurements of thrust and water speed for a ship is very much appreciated.

7. Concluding Remarks

In the present report description has been given on the model-ship correlation method developed in Nagasaki Experimental Tank under the subject of the basic concepts, applications to high block ships together with other kinds

The study on model-ship correlation method in Nagasaki Experimental Tank was originated by Dr. K. Taniguchi, Managing Director, MHI and has been carried out system-actically under his direction. The study on unstable phe-nomenon in self-propulsion tests has been carried out under the leadership of Dr. K. Watanabe, Vice Manager of

Moor, D. I., "Proposed Performance Prediction Factors for Single Screw Ocean Going Ships", 13th I.T.T.C. Report of Per-formance Committee, Appendix 1 (19721.

Lindgren, H., "Ship-Model Correlation Based on Theoretical Considerations", 13th I.T.T.C. Report of Performance Com-mittee, Appendix 2 (1972).

Fraude, R. E., "A Description of a Method of Investigation of Screw Propeller Efficiency", TINA. (1883).

Taniguchi, K., "Model-Ship Correlation Method in the Mitsubishi Experimental Tank", Journal of S.N.A. of Japan No.113 11963), Mitsubishi Technical Bulletin No.12 11963). Watanabe, K., "Repeated Self-Propulsion Test on a Tanker Model", Journal of S.N.A. of Japan No.121 (19671.

Sasalima, T., "A Study on the Propeller Surface Flow in Open and Behind Conditions", 14th l.T.T.C. Contribution to

Per-formance Committee (19751.

Taniguchi, K., "Study on Propeller Open-Water Characteristics - Effect of Boss Ratio" (in Japanese), Transactions of the West Japan Society of N.A. No.3 (1951).

Taniguchi, K., "Study on Propeller Open-Water Characteristics - Effect of Blade Thickness/Chord Length Ratio" (in Japa-nese), Transactions of the West Japan Society of N.A. No.4 (1952).

Acknowledgment

R eferences

of ships and problems to be solved. According to the 13th l.T.T.C. the method is classified as a theoretical one and is almost similar to that proposed by Lindgren(2). This has been applied to speed and power prediction during these twenty years.

The main feature of the method lies in wide applica-bility to various kinds of ships and adaptaapplica-bility for future development in technology. The power prediction is com-posed of such elements as resistance coefficients, self-propulsion factors and propeller open-water characteristics. For the power prediction of high block ships a three-dimensional extrapolation method was introduced, which has been validated by trial analysis and geosim tests carried out later. Presence of the two kinds of flow pattern around stern, a method of distinguishing the type of flow and selecting correlation factors, are described. There are still many problems to be solved on this phenomenon and further study is required especially to cope with increasing fullness of stern. At the same time it is necessary to watch trial results with caution whether such S-type flow appears on a ship.

Nagasaki Technical Institute, MH I.

The author wishes to express his gratitude to them as he is indebted very much to their studies for the preparation of the present report. He thanks also to all members of Nagasaki Experimental Tank for their cooperation in carry-ing out this long term study.

(9) Taniguchi, K. & Tamura, K., "On a New Method of Correction for Wind Resistance Relating to the Analysis of Speed Trial Results" (in Japanese). Transactions of the West Japan Society of N.A. No.18 (1959).

1101 Taniguchi, K. & Tamura, K., "On a New Method of Correction for Wind Resistance Relating to the Analysis of Speed Trial Results" 11th I.T.T.C. Report of Performance Committee, Appendix Xl (1966).

Fulii, H. & Takahashi, T., "Experimental Study on the Resist-ance Increase of a Large Full Ship in Regular Oblique Waves" (in Japanese) Journal of S.N.A. of Japan No.137 11975).

Taniguchi, K., "On the Distance of Approach Runs" 11th

I.T.T.C. Report of Performance Committee, Appendix VI

(1966).

Taniguchi, K., "Propulsion Trial Code" 10th I.T.T.C. Report of Propulsion Committee, Appendix V (19631.

Taniguchi, K., "On the Mitsubishi Experimental Tank, recently Completed" (in Japanese), Journal of S.N.A. of Japan No.96

(1955).

Taniguchi, K., "On Model-Ship Correlation in Propulsive Per-formance" (in Japanese), Lecture at the 70th Anniversary of the Society of Naval Architects of Japan (1967).

Per-formance", Japan Shipbuilding & Marine Engineering Vol.2 No.3 (1967).

Taniguchi, K. & Tamura, K., 'On Blockage Effect", Mitsubishi Experimental Tank Report No.307 (1958).

Tamura, K., "Study on the Blockage Correction", Journal of S.N.A. of Japan No.131 (1972).

Taniguchi, K., "Study on Scale Effect of Propulsive Perform-ance by Use of Geosims of a Tanker", Journal of S.N.A. of Japan No.120 (1966), 11th I.T.T.C. Report of Performance Committee, Appendix XII (1966).

Baba, E., "Separation of Ship Resistance Components" (in Japanese), Symposium of Viscous Resistance (Osaka, May

9-10,1973).

Taniguchi, K. & Chiba, N., "Investigation into the Propeller

Cavitation in Oblique Flow", Nagasaki Technical Institute, MHI Report No.1800 (1964).

Taniguchi, K. et al., "Comparison of Propulsive Performance between Model and Ship of a Hydrofoil Boat", Symposium on Testing Techniques in Ship Cavitation Research (Trondheim, May 31-June 2, 1967).

Taniguchi, K., "Sea Trial Analysis of the Vertical Axis Propel-lers", 4th Symposium on Naval Hydrodynamics (Washington D.C., August 27- 31, 1962), Mitsubishi Technical Bulletin No.6 (1962).

Taniguchi, K., "On the Tank Tests of Fishing Boat Models in Waves", FAO 2nd International Conference on Fishery Boat (Rome, 1959).

Taniguchi, K., "Performance of Ships in Waves" (in Japanese), Symposium on Ships and Waves (Tokyo, June 13- 14, 1961).

Kawaguchi, N. et al., "On a New Analyzing Method of Ship's Service Performance", Journal of the Kansai Society of N.A., Japan No.152 (1974).

Hughes, G., "Friction and Form Resistance in Turbulent Flow, and a Proposed Formulation for Use ¡n Model and Ship

Cor-relation", TINA. (1954).

Taniguchi, K., "Form Factor K Obtained by Resistance Tests

at Low Froude No.", 9th I.T.T.C. Written Contribution (1960).

SR 107 Committee, "Study on the Speed Measurinç Techni-ques of a Ship and the Improvement of the Accuracy of Power Prediction Method" (in Japanese), Report of Japan Shipbuilding Research Association No.142 (1972).

Baba, E. & Takekuma, K., "A Study on Free-Surface Flow around Bow of Slowly Moving Full Forms", Journal of S.N.A. of Japan No.137 (1975).

Taniguchi, K. & Sasajima, T., "Scale and Roughness Effects of Propeller Section Drag", Journal of S.N.A. of Japan No.133 (1973).

Watanabe, K., "Unstable Phenomenon in the Self-Propulsion Test of Full Ship Form Models" (in Japanese), Mitsubishi Technical Review Vol.4 No.4 (1967).

Watanabe, K., "Unstable Phenomenon in the Self-Propulsion Tests of Full Ship Form Models" (in Japanese), Journal of S.N.A. of Japan No.126 (1969).

Taniguchi, K. & Tamura, K., "Study on the Flow Pattern around the Stern of Large Full Ship", Mitsubishi Technical Review Vol.8 No.1 (1971).

Watanabe, K., "Unstable Phenomenon in the Self-Propulsion Tests of Full Ship Form Models" (in Japanese), Symposium on Propulsive Performance of High Block Ships (Tokyo, June

17-18, 1975).

Nagamatsu, T. & Sasajima, T., "Effect of Propeller Siction on Wake", Journal of S.N.A. of Japan No.137 (1975).

Tanibayashi, H., "The Histrical Review on the Propulsion Test Method in Mitsubishi Nagasaki Experimental Tank" (in Japanese), Senpaku Vol.48 No.1 (1975).

Baba, E., "Blunt Bow Forms and Wave Breaking", 'he First STAR Symposium (Washington D.C., August 26-29, 1975).