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
1.5D below 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 0.55
C
0.7
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 ratio from J = 0 to theJ corresponding to K
T
= 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, R
n0.7
, at the 0.7 relative radius should be not less than 3 x10
5
:

( )

2 2
7 . 0
7 . 0
7 . 0
nD V c
R
A
n
+
=

where c
0.7
is the chord length at the 0.7 relative radius of the propeller, and is the kinematic viscosity
of water at the test temperature.
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 3
rd

slowest speed second, the 5
th
slowest speed third etc. Once the highest speed is reached, the test
program continues with the 2
nd
highest speed followed by the 4
th
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 from
about 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 K
T
, K
Q
, and
o
. versus J
A
. 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.