Standard method of measurement and analysis of speed trial data in Nagasaki Experimental Tank

May 1981

MITSUBISHI HEAVY INDUSTRIES, LTD.

;;

NIrusuB}SfJf, TEc1lIt:., 1it

_{in No.145}

Standard Method of Measurement and Analysis of

Speéd Trial Data in Nagasaki Experimental Tank

Standard Method of Measurement and Analysis of

Speed Trial Data in Nagasaki Experimental Tank

Kinya Tamura'

Hidetake Tanibayashi"

Speed trials are carried out both to verify the contractual relationship between the speed and the horsepower, and to obtain model-ship correlation for improvement of ship performance prediction. In order to make the best of trials from scientific

view-point, it is necessary

to obtain as accurate data as possible within the scope of acceptance trial, to analyse them on physically sound basis, and

to develop mode/-ship correlation consistent with prediction method and having wide applicability.

This paper describes the standard method developed in this line in Nagasaki Experimental Tank, along with the efforts and

back-ground materials to establish it.

1. Introduction

Speed trials are carried out to establish the relationship

between the speed, horsepower and propeller revolutions under specified conditions of displacement, draught and trim. From the results it is expected that,

(a> contractual obligations between shipbuilders and ship-owners are verified in relation to speed and

horse-power,

model-ship correlation for different type of ships is

obtained which will improve the prediction of ship's

performance from the model tests, and

the relationship between speed and propeller

revolu-tions is determined as an aid to navigation of the ship.

If (a) is called commercial purpose, then (b) would be scientific and (c) would be operational purpose. Although speed trials are a very limited chance of getting full-scale data which can be compared with prediction from model

tests, there seem to have been many cases where the trial

results may not be sufficiently reliable for subsequent use in scientific analysis.

In order to make the trial data of

really scientific value, it is necessary to obtain as accurate data as possible, to establish a standard method of analysis

and _{to accumulate reliable model-ship correlations, for}

predictions of the performance of a new ship.

If,

_{however, too much stress were laid on scientific}

purpose, a procedure of trials would be too extensive and too expensive to be adopted from commercial viewpoint.

Therefore efforts have been done by Nagasaki Experimental

Tank to make trials as desired from scientific viewpoint

within the scope of acceptance trials.

To this end, a procedure was proposed to shipyards to get data reliable for subsequent analysis with littLe

addi-tional cost, measurements on board ships have been made

by members of the Tank on most relevant data

-

horse-power, propeller revolutions and wind - and a procedure

for analysis of the trial results has been developed which is

Nagasaki Technical institute, Technical Headquarters

simple but physically sound, consistent with the method of

powering and applicable to variety of ships and variation

of circumstances.

In the following

is described a standard procedure of

measurement and analysis developed in Nagasaki Experi-mental Tank with background materials and considerations.

Some comments are added on further investigations for

improvement of the procedure. 2. Execution of standardization trials

The most commonly used method of conducting speed

trials is to make several consecutive runs, alternating in

direction, over a measured distance at substantially constant revolutions of the propeller, measuring the speed, horsepower and propeller revolutions over each run.

How-ever simple the execution of speed trials may seem to be,

there are many interfering factors making results unreliable. Current, wind, waves, restricted depth of water and fouling

of the hull are factors which cannot always be easily

eli-minated. Even with a ship running at constant propeller revolutions, remaining acceleration, if any, would require

additional horsepower corresponding to inertia force.

In order to minimize those interfering factors within

practicable

limit, standard procedures for execution of

trials have been prepared as called code'1, guide21, etc. The standards thus settled at a point of compromise be-tween commercial arid

scientific veiwpoints, are to be

supported by scientific basis.

Distance of approach run is

a typical one of them.

Distance required for acceleration of ships has increased

with increasing size of tankers, since thrust to displacement ratio decreased with increasing size. Based on equation of motion

dV

(1 +a)-- +R

T(1 t)

(1)

g d-r

speed in terms of difference ÌV from final speed

(Lv\

e

-t.Jg/L.r

(1 -e"1

To)

where ii is a function determined by the mode of accele-ration of a ship. For a ship with a diesel engine running

with a constant torque

2 o

-Vs0

\4=

0.001 0.002 0.003 0.004 0.005 0.01 0.02 0.03 0.04 0.05 0.10 0.20 0.30

i/g/L.T0

(2) 0.40 0.5014 -12 -10 -S -6 -4 -2 Time (minutes)

Fig. i Variation of ship speed during approach run

Fig.

i

shows an example of the calculated speed during approach run in terms of difference from the final value.

The results from the calculation are in good agreement with

measured ship speed.

Another subject of growing importance with increasing

size and speed of ships is depth of water necessary to avoid

shallow water effect on resistance. A variety of models

was towed in the Tank - drained to small depth to detect

the critical speed V at which resistance starts to increase

rapidly or squatting occurs>4>. A typical result is shown in

Fig. 2, in which it is noted that an envelope expressed by chain line can be drawn for V/-\/gh irrespective of type of

o

/

Tanker

Cargo ship (full load) Fishing boat

5 10 15

h/d

Fig. 2 Critical speeds in shallow water

ships (with exception for high-speed boats) which tends to

V/'gh

0.6 at

large hid. This asymptote has been applied to estimating critical depth ash>2.75 v2ig.

In planning the speed trials, it is desirable to be

acquaint-ed with nature of the current in the neighbourhood of

the measured mile course in order to avoid excesssive disturbance on the trial results.

To do this, the current

conditions were surveyed at several positions and depths near the course near Nagasaki over a period of time. As a result, prediction of current at any date and hours can be

made based on the regression of the measured data. At the

same time, the measured-mile proved to be free from

unusual disturbance of current.

With such a background on fundamental investigations

into the conditions for the trial, we have proposed standard

procedures for carrying out speed triais. The first authoriz-ed is found in the report of SR41 committee151, in which

standardized speed trials were performed on several large

tankers to get reliable full-scale data and to cope with fast

increasing size of ships. Later, this procedure was extended

for wider application to variety of ships including very

large tankers, and on this basis Taniguchi prepared

Propul-sion Trial Code161 for the ITTC propulPropul-sion committee. A revised edition of this is

called now ITTC guide for

measured-mile trials12>, excerpt of which is given in

Appen-dix.

3. Measurements on board ships 3.1 Items of measurement

The basic data measured on trial include the following:

The time taken to cover the measured course to

cal-culate the ship's speed

The revolutions of the propeller

The horsepower delivered to propel the ship The wind speed and direction relative to the ship The size and direction of sea waves

Among the above, the measurements of horsepowers and winds are most diverse depending on type of ships and main

20 o n .

-qI.iE.r

V °° o 0 i ap

(1t)

i

j'

F2dCA1

2J

i+_

i

2Jq_J01

+i/3FnCt+ 2dF,jJ

(3)

and for a steam turbine driven with a constant power

i ap , ¡',

2J.J,

1+ L

(

F2

dC'l'

+

_1/3hi

(4) 2 _dF,» 0.6 VC o h d Critical speed

Judged from resistance Judged from squat Water depth Draught of

ship

--Cargo ship (trial cond.)

o 2

Tan ker/

speedb0

- 0.5

engines. In many cases, the horsepower of steam turbines on merchant ships are measured by a torsionmeter, those of diesel engines are measured by a pressure indicator or by

rate of fuel supplied, and those of electric motors are

measured in terms of voltage and current. Wind speeds and directions are measured by an anemometer mounted at the top of superstructure.

With a view to obtaining the trial data which can be used as a common basis for a variety of ship and engines, it was

decided to measure the horsepowers and the wind by the staff of the Tank using the same kind of ¡nstrumentation

at the same location on the ships. The decision was made

as far back as in 1950's, and since then both quantities

have been continually measured parallel with the measure-ment by shipyard for contractual purpose.

Other items of measurement, which are not so much influenced by the method of measurement, type of ships

and engines, environmental and contractual circumstances are obtained from the measurement made by shipyards.

3.2 Measurement of torque and propeller revolutions

Among variety of measuring instruments for torque of

the propeller shaft, Togino's torsionmeter of optical type171

has been in use with some modification in Nagasaki

Ex-perimental Tank. For us, this is considered to be most

reliable in view of the purpose of measurement.

Arrangement of the Togino's torsionmeter is shown in Fig. 3 and the scheme of the measurement s depicted in

Prism

Film in camera

Center of Shaft Fig. 4 Optical system of

Togino's torsionmeter

Fig. 3 Arrangement of Togino's torsionmeter

Concave mirror

c

0G) E 100 0 1 2 3 4 5 6 io,

Shift of zero in percentage of °max

60-1

c

0G)

E 40

20

"Originally, electricity for the lighting had been supplied from outside by way of slip rings. They have been replaced by dry cells as

described above, and further attempts are being made to omit the ring ( _{and handle ©by fitting a micromotor to camera®.}

0 1 2 3 4 5 6 7

Difference between a pair of torsionmeters (%) Fig. 5 Accuracy of measurement by Togino's torsionmeter

Fig. 5 (a) shows a histogram for the zero shift between

before and after the trials in terms of ratio to the maximum

torque measured in each trial. Fig. 5 (b) shows the

dif-ference between the torques obtained by the pair of

cameras expressed in a similar way. From the above it can be stated that the measurement error is less than 1%.

For propeller shafts with greater rotational speeds as in the case of high speed boats, tugs, naval vessels etc., Togino's torsionmeter cannot be applied because of large-ness relative to the shafts and excessive centrifugal force on

cameras and other optical systems mounted on the shaft. For such measurements, an electric torsionmeter was

developed18 with inductance type pick-up. Fig. 6 shows an 3

Fig. 4.

The two rings ® and © are mounted on the

propeller shaft with a gauge distance of about 1 meter from each other.

To the ring ® is fitted a source of light ©

which s reflected by the concave mirror- © and

photo-graphed by the 35 mm camera ®. When the torque is to be measured, the ring ® ¡s pushed towards the ring © by

the handle ©, thus turning the roll of the film in the

camera © and switching on the electric supply from the

dry cells © fixed to the shaft". Number of shaft

revolu-tions is measured by photo-electric counter ©. The zero

of the torsionmeter

is

taken before and after the trial

by slowly turning the shaft with turning gears. After the

trial, the film

is developed and enlarged to obtain mean

torque above the zero.

Advantage of this torsionmeter lies in

optical system without mechanical resonance fre-quency,

simplicity in structure without wearing part, and Cc) capable of continuous recording.

Usually a pair of cameras is set on the ring for balance of

weight, for compensating the effect of deflection of shaft,

and for covering the accidental failure in the measurement by one of them.

4

U

_----180

i.---IiIIIIIIOHIS

juil

i!I!IIj'jii

Fig 6 Inductance type electric torsionmeter

8.5

96

Fig. 7 Inductance type pick-up for electric

torsionmeter

example fitted to a shaft of 140 mm ¡n diameter with

maximum revolutions of 1000 rpm.

The displacement

between the two rings (in this case 180 mm distant) is taken up by a pair of El type differential inductance

pick-up as shown in Fig. 7. The measuring system was designed

on the basis of our experience on electric self-propulsion dynamometers19>. The output voltage of the inductance bridge is, after amplification, balanced by variable

resist-ance, thus the torque of the shaft can be read on spot by

0-method.

This type of torsionmeter is featured by its

smallness, simplicity and reliability, and has been applied

to about 30 ships up to the present.

3.3 Measurement of wind force and direction

Measurement by ari anemometer, mounted as usual at the top of the superstructure, is liable to the disturbance due to the structure itself and the radar mast on it. The effects

are so varied with the arrangement around the

anemometer and the direction of wind that it is difficult

to derive a simple correction method. Therefore the measurements by ourselves have been made on a pole

mounted at the bow. This location of measurement can be regarded as best practicable in view of safety and

accessi-bility in preparation and accuracy (with less interference)

of the measured results.

A Robinson type anemometer has been used because of

its simplicity and lightness. Instantaneous recording of

wind force and direction is made in the instrumented room

in the house by way of electric cables connected from the bow.

The wind speed

is calibrated in

a wind tunnel of

Nagasaki Technical Institute up to 30 m/s as a function of wind speed. Potentiometer for detecting wind direction is

calibrated before each trial.

4. Analysis of speed trial results 4.1 Correction for wind and current

Even though a speed trial has been executed in a reason-able way in accordance with such a standard procedure as described above, the results are not free from disturbances

- wind, current and wave - which are not present

in the

towing tank. The propulsive performance predicted from

the model tests for currentless water and calm weather can

be compared with full scale data, only after the effect of those disturbances has been eliminated by analysis of the

measured results.

There are several ways of analysing speed trial results.

The method developed and in

use in Nagasaki Experi-mental Tank is based on a principle to reduce the data to

vacuum (no-air) condition using air resistance coefficient of the above water hull (Fig. 8), and after that analysis of tidal

AR = R wind COS cs

=CxA.kW2

2

Fig. 8 Component of wind force 0.2 0.1 o -0.1 -0.2 Wind speed: W d

1.3 14 1.5

1.6

1.7 18 19 20 21 22

n (rps)

(b) K0 curves of standard and vacuum conditions

Fig. 9 Correction for wind and current

Up

oDown} Trial reS0tS

up

_{i Corrected to vacuum cond.j}

DownJ Corrected

to standard cond. 4Ì

+ Standard cond. Vacuum cond.

i--7 8 9 10 11 12 Time (hour) (a) Analyzed curve of tidal current

(Parallel component with trial course)

12 o 0.026 0.025 0.024 0.023 0.022 0.021

current and correction to no wind condition (with relative wind velocity equal to ship speed) are made. Compared

with-conventional methods of correcting wind effects based

ort the difference of torque coefficients between a pair of

alternating runs, this method is advantageous and renders reliable results especially when the wind blows abeam.

Principal steps of the analysis method is described in

Table 1. Thorough procedure of calculation with

numeri-cal examples is given in ref. (10), from which some typinumeri-cal results are quoted in

Figs. 9 - 10.

Fig. 11 shows tidal

current curve and KQ-N curves obtained from the analysis

of trial data.

Fig. 12 is the final results of correction for

wind and current made on 8 sister ships, in which it can be

seen that the deviation of the corrected speeds is within

±0.2 kn.

4.2 Correction of waves

Though it is generally agreed that speed trials are made

in relatively calm seas, e.g. preferably less than 2-3 in sea state121 (c.f. Appendix), there can be opportunities to

conduct trials in higher seas due to several reasons. There-fore attempts have been made to develop a method of

cal-(15)

vacuum condition

+ V, correction for current from

the difference of speeds (at the same propeller revolutions) between alternating runs

(p8/2)C Ak(o)V2

Similar to (11) Similar to (12) K01 + K02, torque coefficient in calm weather n1 +n2, propeller revolutions in calm weather from K0 - n curve at n=1V5160 V5(n - n2)in vs0 + . V from K03 by (3) - (7) of Table 2 500013 _{14 15 16 17} V (kn)

Fig. 10 Comparison of analysis results of 8 sister ships

Trial resu Ils Computed

Lpplmj Lpp[m]

2 4

Beaufort scale

Fig. 11 Effect of waves on resistance increase

Model test results

[CrJ or [C&K]

[t, WM,71r]

Ship trial results k, SHP, N

V

Model-ship correlation factors ACf =

- C0

ej= (1 - w,..»!

(1 »

Propeller open -water characteristics for ship

Fig. 12 Basic concept of ship trial analysis

18

5 Powers corrected for wind and

current are expressed in the

following SHP=ASHP+f(V5) _+E Where tSHP is varied ship. for each

w

© ..,_

o 210-225

--- 215

® 225 - 285 250 300-325 310

Table i Correction for wind and current

x10 (1) vs (kn) Ship speed

(2) N5 (rpm) Propeller revolutions

2

(3) SHP (PS)

Shaft horsepower measured in trial

(4) w

(mis) Relative wind speed

(5) e (deg) Relative wind direction

(6) K00

from SHP and N5 (cf. Table 2) o.

(7) (Pai2)Cx Ak(0)W2

(8)

.Ri p(1 t)v2D2

(9) J

from open-water characteristics at K00

(10) from open-water characteristics for

r

(11) LK01 do.

(12) ¿n1

n.AJ/J where n=N5i60

(13) K01

K00 + ¿K01, torque coefficient

in vacuum condition

(14)

nl

n +&1, propeller revolutions in

17500 15500 o-Q, 12500 10000 7500 R0

J(2

n2 K02 n2 K03 LW vs SHP

culating resistance increase due to waves and to correlate the results with trial data.

Derivation of effect of waves from trial results, however,

cannot be done so simply because scatter of the results corrected for wind and tide are not ascribed solely to the effect of waves. With this in mind, however, resistance

increment above the value predicted for calm water

(without current and wind) were plotted to the base of

sea state. The plotted results presented in Fig. 11M1)h121

are, though scattered considerably, are arranged

in the

order of calculated results. With further accumulation of such data, access will be made to correction for effects of

waves.

5. Development of model-ship correlation

5-1 Model-ship correlation method in Nagasaki

Ex-perimental Tank 31,114)

In the first stage of tank testing, any means for predict-ing ship's performance from mode! tests was regarded as

a model-ship correlation. In the course of the progress in

technology and accumulation of data, however, the scope

of model-ship correlation has been restricted because of the

basic assumptions in the separation of resistance

compo-nents, scale effects on self-propulsion factors and so on. In view of such developments, a correlation method has been required.

to be flexible for development of shipbuilding

tech-nology and model test technique, to be applicable to wide variety of ships,

to be applicable to ships in seaway and with fouling

on hull and propeller,

to be applicable to the ships with propulsors other than screw propellers, and

to be simple and have practicable accuracy.

Usually three kinds of data,

i.e., speed, horsepower

and propeller revolutions are measured on trial. Therefore

the correlation between the model and the ship is reduced

to the selection of two independent factors. In view of the

above mentioned requirements for application, and

con-sidering further that the correlation data are better

supported by physical meanings, the two correlation factors

-Cf on viscous resistance and e1 = (1 - wm)/(1 - W) Ofl wake fraction - have been adopted.

Basic concepts of ship trial analysis and prediction of

power are shown in Figs. 12 and 13, respectively. They are

based on the assumption that the influence of propeller

loading on self-propulsion factors can be neglected and the open-water characteristics are evaluated at a standard

Reynolds number.

lt

is further assumed that the scale effects on thrust deduction and relative rotative efficiency are neglected and that self-propulsion factors do not vary with propeller loading. The procedures of calculation for trial analysis and prediction of power are shown in Tables

2 and 3, respectively.

This method of model-ship correlation has been used

G Model Sh p Correlation factors Cf, e1 V3 (kn) N3 (rpm) SHP (PS) DHP K0 rs K00 J

Kr

w5

e or

T ts R

R0

cts rSO ACf

}

Power & N for ship Propeller open-water

character-istics for model

'ç,-Propeller open-water character-istics for ship

Fig. 13 Basic concept of speed and power prediction

since as early as 1950's with slight modification due to

appearance of high block ships, adaptions to multi-screw

ships, etc. As a matter of fact, this method could cope with

change of circumstances such as adoption of eletric

weld-ing in place of rivetweld-ing in ship's construction, and practicweld-ing

of turbulent stimulator in model testing. Wide range of

application

was explored without difficulty

to

multi-screw ships, high-speed boats, ships with vertical axis pro-peller and analysis of service performance.

5.2 Relation to 1978 ITTC performance prediction

method

In 1978 the ITTC Performance Committee presented

1978 ITTC Performance Prediction Method for Single

Table 2 Ship trial analysis

Ship trial results (corrected for wind and current)

= SHP - (stern tube friction loss 75DHP/(2irpn3D5) x 1/(No.of

propellers), rz=N3160

7?rs'tlrM (from self-propulsion test)

K0 X

from propeller open-water chara teristics through K00 (7) 1 - w5 = JitO/y5, v5=051444 x V,

eI=(1wM)/(1wS), Aw=wM_v,

pn204 x K

t5 = tM (from self-propulsion tesi

T(1 t3)

- Ra1XRa =

difference of a resistance between model and ship in no-wind condition Non-dimensional expression of

total resistance R0

Total resistance of ship derived

from model test [(Cr+Cfso or

C +C0 (1 +k)}

Cf, -

= ¿Rf/(p/2)v,2S ir

)

Resistance test Self-propulsion test

[Cr] or [C&K)

Table 3 Power calculation of ship

';

(kn) L/v císo Cro Rro

J

flHS DHP (PS) SHP (PS) N (rprrù D = propeller diameter

found from propeller open-water

characteristics through \/KT/J (15)

(1 -t)/(1 w5)

77rs = 77rM (from self-propulsion test)

Q.P.C., ?7ap7Hsrs

EHP/lla

DHP + (stern tube friction loss)

60 V/JD

Screw Ships15'. This method was established as a result from tireless efforts of 13-15th Performance Committee, The method in use n Nagasaki Experimental Tank follows

substantially

the same procedure as the ITTC method

except for the open-water characteristics used for predic-tion of power.

According to the ITTC method, the open-water

charac-teristics of a full-scale propeller are calculated from the model characteristics with correction for scale effect on

section drag coefficient, while in Nagasaki full scale propel-ler characteristics are taken as those of model obtained at a standard Reynolds number.

The standard Reynolds number is defined by

Re(k) C07 2

+ (07nD)2 = 4.5 x iO

where C07 is the chord length of propeller blade at 0.7R. The value of Re(k) was chosen from the zone where the

scale effect on open-water characteristics decreases. Fig. 14 shows as an example16 that KT tends to a constant, while

K0 continues to decrease over Re(k) = 4.5 x iO5. Though a critical Reynolds number may exist in higher Reynolds number, it is impracticable to adopt it because of capacity

of propeller dynamometer and towing carriage.

-

---fI_O 4

310

-o.. s

0.0100 _{1 2 3 4 5}

Re(k) x 10

Fig. 14 Effect of Reynolds number on open-water characteristics of propeller

lt is a practice in Nagasaki Experimental Tank, therefore,

to test a model propeller in open-water at the two Rey-nolds numbers, the one corresponding to self-propulsion

test and the other at the standard Reynolds number. When

the model propeller is not geometrically similar to the ship

propeller, the full scale characteristics can be estimated on the basis of test results at standard Reynolds number with

correction for the difference in particulars of the propeller. A standard procedure for the correction of the open-water

characteristics has been prepared.

The above statement does not necessarily means that

scale effect on open-water characteristics can be neglected.

Calculations were made by Taniguchi applying correction between the standard Reynolds number and full scale

including roughness effect(17). Further works are underway to investigate into scale effect on propeller characteristics. For the time being, propeller characteristics at the standard Reynolds number are used for propeller design, prediction

of power and analysis of trial results to conform a

con-sistent system.

5.3 Efforts for improvement of model-ship correlation The model-ship correlation data analyzed by the method mentioned above have been based on the present practice of model tests and full-scale measurement and correction. Looking at considerable scatter of ACf and e, as plotted to Reynolds numberll3),(14)

it

is recognized that further efforts should be made to improve the model-ship correla-tion. _{Among the various efforts made in both model and}

full-scale measurements, attempts at improving the correc-tion for wind and waves are described in the following.

7

between model and ship in no-wind condition EHP (PS) R. v/7S, effective horsepower

ts

t = t

(from self-propulsion test)

T

_Rr/(l

e1 _{from model-ship correlation data}

ws

1 w5(l vvM)/eI

VP

(1 we)

1kij=

calculated by (11), (14) and D,

Ship speed (given)

Froude's numbers,

=0.51444,

L = ship water line length

Reynolds numbers at 15 C and sea water

from correlation line

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

Cr+CfSO+Cf or CW+CfSo(l-1-k) +Cf

(Cr or C and k are derived from model test) Total resistance

'ero +R. LRa = difference of air resistance,

J=0.4 J=0.5 I = J=0.6 Mark D(mm) + 130 217 0.25 0.20 0.15 0.10 0.025-0.020 0.015

As mentioned in 3.3, the wind speed and direction have

been measured by an anemometer mounted on a pole at

the bow, but with the appearance of VLCC and ULCC

having such a fullness as ranging from Cb = 0.83 to 0.86,

certain effects have been expected of their blunt bow. And

therefore wind tunnel tests were carried out on a partial bow model (Fig. 15). The results indicated that the devia-tion

of measured wind speed and direction from the

undisturbed values increases with angle of incidence; e.g.

Fig.15 Partial bow model of a tanker for wind tunnel tests

'0.8OOm

Float

E

o

Fig. 16 Wave height recorder of pendulum type

increment in speed exceeds 10% of the undisturbed wind

speed and the direction deviates by more than 20 degrees.

To improve the accuracy of correction for wind, it

is

re-commended therefore to conduct wind tunnel tests on

typical classes of ships and to collate such data.

In order to establish a method of correction for waves,

it

is essential to get wave data measured with reasonable

accuracy. Development of wave height probe has thus been anticipated which is suitable for use in speed trials. In view of the purpose of the measurement, the probe is

preferably equipped with self-recording device or radio

transmitter. Fig. 16 shows a pendulum type wave height

recorder(18) developed in late 1950's which measures static

pressure underwater varying with surface wave height.

This probe was used for full scale test of a high speed naval craft and successful results were obtained

Recently another type of wave height probe was

devel-oped which measures acceleration of a buoy. With a device

eliminating the interference with inclination of the buoy, the measured signals are integrated twice to obtain wave

height. This probe was used to evaluate resistance increase of VLCC's in waves mentioned in 4.2.

6. Concluding remarks

The standard procedure described above is evidently a system coupled with the part performed by shipbuilders. In this respect, Nagasaki Experimental Tank owes very

much to the situation that it belongs to a potential

ship-builder. As a matter of fact, this standard could not have

been developed without collaboration of Nagasaki Shipyard

& Engine Works and other shipyards of Mitsubishi Heavy Industries, Ltd. The shipyards have been willing to

dis-cuss with the Tank the practicability of standardization

trials, and to render service to measurement of horsepower and wind on board.

For further improvement of model-ship correlation,

efforts for reducing the scatter of full-scale data are of

primary importance. To this end, it is desirable to include measurement of thrust and roughness in full-scale. Study

on effect of current across the course and on simpler

practical method of estimating wave effects will render

valuable information. Scale effects on propeller open-water characteristics and self-propulsion factors are to be

promoted.

Further on model scale, study on unstable

phenomenon is directly related to model-ship correlation.

It is

surprising that there are too many to do, to

proceed one step further. Some of them are underway, but

in

order to promote it further, cooperation of various

institutions in various fields is indispensable and certainly

1. General

This guide is intended to outline a procedure for obtain-ing data on measured-mile trials so that the results may be

of scientific value and be used

in the development of

model-ship correlation,

2. The trial conditions of ships

Time out of dock is

desirable to be less than two weeks.

The sea state is preferably less than 2 3. The

weather and sea should not cause the ship to have

noticeable motions.

3. Number of runs

Measurement should be made for not less than four speed groups.

A thorough analysis of the currents is essential in order to derive the speed of the ship through water, and

¡n this connection consecutive runs should alternate in

direction over the measured mile. 4. Measured mile course

lt is essential to choose the course where the tidal effect

is not large and sufficient space for approach runs and

manoeuvring is available. The minimum depth of water h acceptable may be estimated by the largest value of the

following two equations:

h >3\rBxT

and

h > 2.75 V2/g

where B is the beam,

T is the draught and V is the speed of the ship 5. Operation of ships during the trials

The operating procedure should be directed towards maintaining steady engine rpm.

Course is recommended as shown in Fig. A.

Recommended position of tidal current meter

-Measured mile

Fig. A The recommended course

9 Nomenclature

A Frontal area above water line of a ship T Thrust of a propeller

a

Slope of Kr - J curve, Kr = a(JJ)

t

Thrust deduction fraction

-S

L' 0.7 Chord length of propeller blade at O.7R Vs Ship speed in knots

C0 Frictional resistance coefficient VC Speed of tidal current in knots

Cr Residual resistance coefficient V Ship speed in rn/s

Ct Total resistance coefficient

VC Critical speed in shallow water

Cw Wave-making resistance coefficient VP Advance speed of a propeller

C Wind resistance coefficient

w

Relative wind speed

Cf Model-ship correlation for resistance coefficient w Wake fraction

D Diameter of a propeller Added mass coefficient

d Draught of a ship Displacement of a ship

e Model-ship correlation of wake fraction _'7a Propulsive coefficient

Fn Froude number of a ship 77H Hull efficiency

g Acceleration of gravity Propeller efficiency

h Depth of water Relative rotative efficiency

J Advance ratio of a propeller o Relative wind direction

Jr J value at zero thrust, Kr = a(JJ) n2D4/g

Jq J value at zero torque, K0 = b(Jq_J) V _{Kinematic viscosity of water}

K0 Torque coefficient of a propeller P Density of water

Kr

Thrust coefficient of a properller _{Pa Density of air} k Wind direction coefficient T _{Time, and Kr/J2}

L Length of a ship 1I _{Coefficient defined in Eqs. (3) and (4)}

N Propeller revolutions per rriinute _{V Volume of displacement}

'J Propeller revolutions per second

Q Torque Suffixes

R _{Resistance of a ship} M Model

Re (k) Reynolds number according to definition of

o

Initial value

s

Kempf

Wetted surface area of a ship

s

Ship

C. Distance of approach runs depends on the accelera-tion characteristics of the engine, on the rate of speed

loss in the turn, and on the engine output relative to the displacement of the ship. At present, there is no

defini-tive criterion to determine the minimum acceptable

length of approach run. In the meantime, however, the following values may serve as a guide:

High-speed cargo liner in light draught at any power

rating above half power: 25 ship lengths

Tankers of 65,-100,000 tons dwt at full load draught

at any power rating above half power: 40 ship lengths

E. Turning at ends of runs should be made with a

mini-mum of helm to avoid excessive loss of speed. 6. Items of observations and measurements

Geometry of propeller

Surface roughness and structural roughness Draught

Temperature and density of water

Displacement is to be calculated from the draught

and the density of sea water measured.

Weather

10

StandardizatIon Trials Code, SNAME (1949)

ITTC Guide for Measured-Mile Trials, 12th ITTC, Report

of Performance Committee Appendix I 11969)

Taniguchi K., On the Distance, of Approach Runs, 11th ITTC, Report of Performance Committee Appendix VI 119661

(41 Tamura K., Resistance Tests in Shallow Water on a Variety

of Ship Models Ito be published)

SR41 Research Committee, Investigations into the Propul-sive and Steering Performances of Super Tankers, Rep, of Shipbuilding Association of Japan, No.31 (19601

ITTC Propulsion Trial Code, 10th ITTC Appendix V, Report

of Propulsion Committee 119631

(7) Togino S., Togino's Torsionrrieter, Journal of SNAJ, Vol.

54 (1934)

18) Taniguchi K. and Watanabe K., A New Electric Torsion'

meter for High Speed Naval Craft, Journal of SNAJ, Vol.

108 11960)

Taniguchi K. and Watanabe K., A New Electric

Self-propul-sion Dynamometer, Proc. of Symposium on the Towing

Tank Facilities, Instrumentation and Measuring Techniques,

Zagreb (1959)

Taniguchi K. and Tamura K., On a New Method of Correc-tion for Wind Resistance Relating to the Analysis of Speed

References

The speed and the direction of the wind relative to the ship by use of an adequate anemometer and wind vane during each run. These are to be positioned at a

favourable height at the bow, or on a mast clear of

interference from the hull and the superstructure.

Sea state

Pitching and rolling

Ship speed (ground speed) is to be calculated from

the recorded time and the length of the measured

course.

Propeller revolutions are to be calculated from the recorded time and the total revolutions during tne runs

over the measured course.

Shaft power is measured by a torsionmeter which is

preferably capable of recording the torque continuously or the mean value through each rotation of the shaft.

lt

is desirable that the torsionmeter and its shaft be

calibrated.

The zero of the torsionmeter should be taken imme-diately before and after the trials by rotating the shaft

slowly in both directions.

Trial Results, 11th ITTC Report of Performance Committee

Appendix Xl 119661

Takahashi T. and Tsukamoto O., Effect of Waves on Speed Trial of Large Full Ships, Journal of Soc. of Naval Arch. of West Japan, No.54 (1977)

1121 Nakamura S. and Fujii H., Nominal Speed Loss cf Ships in

Waves, Symposium on PRADS 119771

113) Taniguchi K., Model-Ship Correlation Method in the

Mitsubishi Experimental Tank, Journals of SNAJ, Vol. 113 (1963), and Mitsubishi Technical Bulletin, No. 12 119631 Tamura K., Speed and Power Prediction Techniques for High

Block Ships Applied in Nagasaki Experimental Tank,

Mitsubishi Technical Bulletin, No. 103 11976)

ITTC Performance Prediction Method for Single Screw Ships, 15th ITTC Report of Performance Committee 119781

Taniguchi K., Study on Scale Effect of Propulsive Per-formance by Use of Geosims of a Tanker, Mitsubishi

Technical Bulletin, No.39 11966)

1131 Taniguchi K., On Model-Ship Correlation in Propulsive Per-formance, Japan Shipbuilding & Marine Engineering, Vol. 2

No.3 119671

(181 Taniguchi K., Pendulum Type Wave Height Recorder, Journal of Soc. of Naval Arch. of West Japan, No. 16 (19601