Comparative seakeeping tests

Searbeiter:

G.Collatz

Tog:

3o.S.1963

HAMBURG MODEL BASIN (HSVA)

Hamburg, August 3o, 1963

prepared by

Comparative Seakeeping Tests (ITTC)

A report submitted to. the Seakeeping

Committee of the

10th

International Towing Tank Conference

London 1963

Hamburgische

Schiffbau-Versuchfranstalt GmbH.

Introduc t ion - =

Tie results of seakeeping experiments conducted by the towing tanks of various countries were compared for a model of the Series 60, 0.60 block coefficient, as part of the

₁₉₅₄

International Towing Tank Conference (ITTC). Agreement among the tanks was

found to be completely unsatisfactory. To eliminate some of the more obvious factors which might influence the results, such as differences in model size or In test methods, the Committee on Seakeeping of the ITTC initiated a controlled program to compare the results of model tests in waves conducted by the David Taylor Model Basin (TrB), the Netherlands Ship Model.Basin (NSMB), and the Admiralty Experiment Works (AEW), The program specified a

large number of head-sea variations using the same 10-ft model in all three tanks ,The results of these tests are communicated in TMB Report

_1309.

In order to control the wave test methodes at the Hamburg Model Basin (HSvA) in the last year corresponding tests have been run with a ₁₅ ft model. In this report a brief description of the methodes at the HSVA is given. The values of the original measured datas with respect to resistance, shaft rpm, torque, thrust, heave amplitude and pitch amplitude are communicated and as far as

possible compared with the results of TILB,NSMB and AEW. Phase angles have not been mea8ured.

Model and Proelier Particulars

Because the wave generator and the equipment for seakeeping

experiments at 'HSVA are adapted for models of about 6m length, the tests could not be done with a 10 ft model. Therefore it was resolved to build a 15 ft model as a compromise between the

original 10 ft model and the models usually employed at HSVA. The model was constructed from plastic and Fiberglas. Also a

corresponding propeller was build. The particulars of model and propeller are listed in the foilowiug table. In

Fig.2

the

character-istic curves of the HSVA propeller and the original TMB propeller are compared.

Beorbeiter: C. Collatz

_{Tag:30.8.1963}

2

Beorbeiter: G. Collatz Tog: 30. 8. 63

Table of model and propeller particulars

Model: Nr 1512

Length between perpendiculars 4.572 meter

Beam 0.609 meter Draft . 0.243 meter Displacement 410 kilopond Waterplane coefficient 0.71 Block coefficient 0.60. Propeller: Nr

1147

Diameter

_159.4

millimeter Number of blades ₄

Exp. area ratio 0.73

Pitch / Diameter 1.064

The distribution of weights in the model was adjusted for the proper radii of gyration as well as for the trim. A longitudinal

radius o,f gyration of 1.157 in ( 0.253Lpp ) was measured by bifilar suspension.

Test Facilities and Test1n Procethire

The seakeeping experiments have been performed in the HSVA deep

water basin on april, 4; may, 8 and

_9;

june, 26 and 27

_1963.

The basiii is 200 meter long, 18 meter wide and 6 meter deep. A carriage on fixed rails spans the width of the basin. Waves are generated from one end of the tank by a plunger wavemaker.

The test program included a range of model speeds from 0 to 2.3 meter/second in calm water and in waves with lengths of 75, 100,

?5 and 150 percent of the model lendth L. Two series of tests were performed: one with constant wave height corresponding to

L/48,

and a second series with wave height corresponding to _./30 ( constant wave slope ). The resistance test which took place

first, indicated that the model used has relatively poor

sea-keeping characteristics. These include low pitch and heave damping, low resonant speeds, and inadequate flare and freeboard. By that large motions and extreme wetness are generated in the more

3

Bearbeiter: Q. Collatz Tog: 30. 8. 1963

_-4

severe wave conditions. ( See the two photographs Fig. 31.) Therefoi'e

it was renounced to accomplish the other measurements in waves with a heightcorresponding to _./3O.

During the experiments the model was joined with the carriage by wires, which run over rolls. Weights fore and aft served for guiding the model in its direction. For measuring resistance the forward directed wire was connected with an electric d,ynamometer, a daniper and a spring. ₍ See Fig. 1 ) These guiding allows the model freedom

in pitch and heave. Freedom in surge, therefore, is affected somewhat by the action of the spring. The damper was necessary to reduce the free surging during the start of each experiment. The spring was so that the swinging system was overcritical.

The test procedure for measuring shaft rpm, torque, thrust, heave and pitch amplitude was to operate the carriage at a predetermined

spee'd and to adjust the revolution of the propeller until the model has the same speed as the carriage. To compare the results of rpm with the results of the 10 ft model the propeller loading was

corrected aecordiigto Reynolds number.

For particulars of the measuring equipment see the following table.

Wave Recording:

Carriage Speed Measurements:

RPM Measurements:

Resistance Measurements:

Torque and Thrust Measurements :

Heave Measurements:

Acceleration Measurements:

Pitch Measurements:

Sonic-Wave -Recorder,

travelling with the carriage

Time and Distant Marks on a revolving drwn

Revolution Marks on the same drum

Eaectric-Ring-Dynamometer (Straingauges)

Electric Dynamometer (Straingauges)

Calculated from acceleration

Electric Accelerometer (inductive)

Gyro-Horizon

-5

Test Results

The original values of the results arid faired curves are plotted against the velocity of the 15 ft model. For particular the

following figures show:

Fig. 3 Resistance (pond) in Calm Water and. in Waves with a Height corresponding to L/48 plotted against the Velocity of the Model

(meter/second)

Fig. 4 Resistance (pond) in Waves with a Height corresponding to

/30 (constailt Wave Slope) plotted against the Velocity of the

Model (meter/second)

Fig. 5 Revolution (1/second) of the Propeller in Calm Water and

in Waves of Height corresponding to L/48 plotted against the Velocity of the Model (meter/second)

Fig. 6 Torque (cm pond) in Calm Water and in Waves with a Height corresponding to L/48 plotted against the Velocity of the Model

(meter/second)

Fig. ₇ Thrust (pond) in Calm Water and in Waves with a Height corresponding to L/48 plotted against the Velocity of the Model

(meter/second)

Fig. 8 Heave/Wave - Height Ratio in Waves with a Height

âorresponding to L/48 plotted against the Velocity of the Model

(meter/second)

Fig. ₉ Pitch/Wave - Slope Ratio in Waves with a Height

corresponding to L/48 plotted against the Velocity of the Model

(nieter/second)

To compare the results with the results from TMB, NSMB and AEW due to Froudos law from the faired curves resistance, shaft rpm, heave and pitch ratios are calculated for a 10 ft model and

plotted against the velocity of the 10 ft model in knots. Fig.10

til Fig.30 shows the confrontation with the original values taken

from the TMB Report

_1309.

W240 PM

Beorbeiter: Q.Collatz Tog:

o.8.63

Conclusion

During the experiments it became evident that the measuring apparatus and methodes are not responsible for the partial unsatisfactory results of the comparative tests but the waves. In the range of the tested wave lengths the wave generator is not

operatin under optimum conditions therefore the waves are not completely uniform. That effect became worse because of the unsatisfactory seakeeping characteristics of the model.

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Comparison of Heave/Wave Height

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Comparison of Pitch/Wave

Slope Ratio between

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Comparison of Pitch/Wave

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Comparison of Pitch/Nave - Slope Ratio between