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Engr 5011 Resistance & Propulsion of Ships Open Water Propeller Performance Laboratory: Winter, 2008

lab2-2008.doc

Brian Veitch, EN4042, Tel: 737-8970, e-mail: bveitch@engr.mun.ca

Purpose

The purpose of the open water propeller performance laboratory is to become acquainted with the

process of planning and executing a model propeller open water performance test, and analyzing the

data in order to make a propeller performance chart. Keep a detailed log (1 per team) of the

experiment.

The test data are to be analyzed in accordance with the procedure provided.

Model Preparation and Setup

Please handle the model propeller with great care. It is very expensive.

The main equipment is listed following:

- 250mm model propeller (B4-55), spacer, fairing cone, set screw, key, dummy hub

- propeller open water performance boat (opens boat)

- shaft dynamometer, tachometer, temperature probe

- carriage, integrated instrumentation, and tow tank

The model is to be fitted to the shaft along with the associated spacer and fairing cone. Ensure that

both the cone nut and internal set screw are secure. Treat the tail shaft with care: do not apply bending

loads to it as these will cause the shaft to bend and damage the opens boat.When installing and decommissioning the opens boat setup, care should be exercised to ensure that

water does not get into the boat. Secure the boat rigidly to the carriage. The shaft should be at least

1.5Dbelow the water surface.Measure this depth.

A data sampling rate of 50 Hz with a low pass filter of 10 Hz is appropriate.

Note the installation and any calibration procedures.

Table. B4-55 propeller data

D 249.67 mm

Z 4

EAR 0.55C0.7 73.86 mm

Test Plan

Experiments are carried out at a constant propeller rate of rotation with the speed of advance

covering the range of advance ratiofromJ = 0to theJ corresponding to KT= 0, with at least one run

with negative thrust.

Prepare a test plan that incorporates the requirements of the analysis. Each group is to test at one

constant shaft speed. Plan your test program so that you get at least 15 equally spaced points over the

test range. Each condition should be tested for at least 5 seconds in steady conditions.

The local Reynolds number,Rn0.7, at the 0.7 relative radius should be not less than 3 x105:

( )

22

7.0 7.07.0

nDVcR

A

n

+=

where c0.7 is the chord length at the 0.7 relative radius of the propeller, and is the kinematic viscosity

of water at the test temperature.

8/12/2019 lab2-2008

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Engr 5011 Resistance & Propulsion of Ships Open Water Propeller Performance Laboratory: Winter, 2008

lab2-2008.doc

Brian Veitch, EN4042, Tel: 737-8970, e-mail: bveitch@engr.mun.ca

Note that it is good practice to stagger the test program to avoid running all tests in either ascending

or descending order. To avoid this, tests can be run so that the slowest speed is tested first, the 3rd

slowest speed second, the 5th

slowest speed third etc. Once the highest speed is reached, the test

program continues with the 2nd

highest speed followed by the 4th

highest speed etc. Better still,

randomize the test order (but avoid starting with the highest speed).

Measure the water temperature at the beginning and end of the program.Note that it is required that you check the measured data (shaft speed, thrust, and torque, and carriage

speed) at the end of every run. The check includes checking the time history for any anomalies and

plotting the results. For example, the simplest check would be to plot measured thrust and torque

versus model speed. If an outlying point is found, the test should be repeated. Also, if the plotted

curves have more curvature over a particular range of speeds, runs can be added or substituted in order

to fill in the curves. A laptop would be useful for this purpose.

It is appropriate to repeat a number of tests to check the repeatability of the measurements.

Procedure

Measure friction in the bearings at the start and the end of the test program. Friction is measured with

the propeller replaced with a dummy hub. Five values of shaft speed should be used, spaced fromabout 10% below to 10% above the shaft speeds used in the tests.

After calibrations have been done, and before testing, the instrumentation must be carefully zeroed.

Thrust is also zeroed in this procedure, but as there is a potential problem with static friction on the

shaft, a more reliable way to deal with thrust zeroing is to measure it when the shaft is turning over

very slowly (as slow as practical ensuring no thrust is developed by the propeller).

A short (10 second) record with the carriage stationary and the shaft rotating very slowly is made

before each test run. This measured thrust is the tare value, or, in effect, the zero value of thrust.

Caution must be exercised because thrust is tared at non zero values of shaft speed and torque.

Corresponding tare values must not be applied to either torque or shaft speed (which is why these must

be carefully zeroed at the start of the tests.

After each run, data are selected over the steady-state condition interval. Any transients at the start of

the steady-state speed interval are excluded from the selection.

Shaft friction torque measured before and after a series of test runs are plotted together against shaft

speed and a mean line is drawn through them. The friction associated with each shaft speed is obtained

by interpolating the mean line at the test shaft speed. The test friction is subtracted from the mean test

value of shaft torque to give the propeller torque used in subsequent analysis.

Analysis and Reporting

Use the spreadsheet provided to record and process your results, making any necessary

modifications.

Tabulate and plot KT, KQ, and o. versusJA. Fit polynomials to these and report the coefficients (4

th

order should suffice).

The report is to describe the test procedure, model, analysis method, and plotted and tabulated results

(specified above), date, and water temperature. Include uncertainty analyses as discussed in class.

The report and the experiment logbook are to be presented to Dr. Veitch by March 27, 2008.