1.
0 OBJECTIVES
To obtain self-propulsion point for given ship speed and loading conditions as
follows:
i. Speed : 16 knots (prototype), 4.62 knots (model)
ii. Draught, T : 2.002 m
iii. Trim : 2° by bow
2.0 SIGNIFICANCE OF SELF PROPULSION TEST
Self propulsion test is carried out by propelling the ship model with a given
propeller. When a propeller has to work behind a ship, there exist interactions between
the ship hull and the propeller. Both hull and propeller are affecting each other and
therefore self propulsion test is carried out to investigate the effects, hence determine The
self-propulsion point for given ship and the loading condition.
3.0 APPARATUS
The apparatus for self-propulsion test are as follow:
i. Overhead crane (Capacity: 5 tones)
ii. Towing tank
Particular Value (m)
Length 120
Width 4
Depth 2.5
Useful Length 90
Table 3.1: The towing tank specifications
condition value
Fresh water temperature, T (°C) 27
fresh water mass density ,ρ (kg/m3) 997
Fresh water kinematic viscosity, ν (m2/s) 0.85409
Table 3.2: Standard values for tank’s conditions
**Derived from ITTC – Recommended Procedures and
Guidelines (7.5-02-01-03)
Figure 3.1: Towing Tank
iii. Towing carriage
Particular Value
Distance between rail approx. 4.45 m
Distance between wheel axles approx. 6.8 m
Carriage net weight approx. 18 tones
Materials steel
Wheels approx. 800 mm
Guide wheels 300 mm
Speed range 0.1 m/s to 5 m/s
Maximum deceleration 1.0 m/s2
Maximum acceleration 1.0 m/s2
Deceleration emergency off (disk and air brake) approx. 2.0 m/s2
Rail shoe emergency braking approx. 5.0 m/s2
Table 3.3: The towing carriage specifications.
iv. Force transducer (Strain gauge)
Value
Particular
Brand SENSOTEC
Type semiconductor
Capacity 500N
Input resistance: approx 370 Ω
Output resistance approx 350 Ω
Excitation voltage 10 Volts maximum
Non-linearity/Hysteresis (max) +/- 0.15% F.S.
Non-repeatability (max): +/- 0.1% F.S.
Overload, safe 50% over capacity
Calibration factor 1.6031 MV/V
Table 3.4: The Transducers Specification
v. Data acquisition and analysis system (DAAS)
Figure 3.2: Data Acquisition and Signal Conditioning System Diagram
Figure 3.3: Dewetron Data Acquisition and Analysis Unit
vi. Crewboat model (MTL023)
Particular Prototype Model
LOA (m) 34 2.83
LPP (m) 30.2 2.52
LWL (m) 31.09 2.59
Breadth (m) 7.6 0.63
Trim (°) 2° (B) 2° (B)
LCG (m) 14.661f 1.222f
VCG (m) 2.78 0.23
Wetted Surface Area, S (m2) 239.2 1.6611
Midship Area Coeff. 0.615 0.615
Block Coeff. 0.425 0.425
Prismatic Coeff. 0.691 0.691
Waterplane Area Coeff. 0.9 0.9
Table 3.5: The Model Particulars.
vii. Self-propulsion equipment
a) Dynamometer
Torque-thrust transducer (to measure torque and thrust)
- Maximum torque: 8 Nm
- Maximum thrust: 220 N
Optical rotary encoder (to measure propeller speed)
- Maximum speed: 5000 RPM
- Pulses per revolution: 60
Gear box
- Ratio: 1: 3
- Maximum speed: 3300 RPM
- Oil filling: 185 cm3
b) Electric motor
Brushless electronically commutated DC motor by 4-quadrant servo
amplifier
Manually operated from control box situated at the measuring rail of
carriage
Nominal torque: 4 Nm
Impulse torque: 15 Nm
Maximum speed: 3350 RPM
c) Propeller
Particular Full Size Model
Diameter, D (mm) 1653.36 137.78
Pitch at root (mm) 1373.28 114.44
Pitch at 0.7R, P0.7 (mm) 1373.28 114.44
Pitch at blade tip (mm) 1373.28 114.44
Pitch ratio at 0.7R, P0.7/D 0.831 0.831
Boss-diameter ratio, d/D 0.193 0.193
Expanded blade area ratio,AE/A0 0.581 0.581
Number of blades 4 4
Table 3.6: Particulars of Propeller
4.0 BACKGROUND THEORIES
Before performing the self-propulsion test, there are several other tests that should
be ran as to obtain the information about the resistance that acts upon the hull and the
characteristics of the propeller that will be used in the self-propulsion test.
Firstly, resistance test should be performed in order to obtain the resistance force
required to run the ship model at certain constant speed. Then open water test should be
run to obtain information about the propulsive characteristics of the propeller. After both
tests have been performed, the self propulsion test can be carried out to obtain the self
propulsion point of the ship model which then can be extrapolated to obtain the self
propulsion point for the real ship.
In self propulsion test, the ship model will be propelled by propeller model that is
powered by electric motor. There are three methods that can be used to perform self
propulsion test which are load varying method, speed varying method and mixed loading
method but in this experiment only load varying method will be used.
There are two analyses that should be determined in this experiment which are
thrust identity analysis and torque identity analysis.
Thrust coefficient:
where
T = Thrust
Torque coefficient: n = Propeller speed
D = Diameter of propeller
Q = Torque
Va = Advance speed
Advance coefficient:
Thrust:
4
T s =K T ρn 2 D
s
Torque:
Qs =K Q ρn 2 D 5
s
To obtain speed of model:
Vs
Vm=
√λ
4.1 Load varying method
In load varying method, the ship model should be propelled by propeller at
different value of loading while keeping the model speed constant. Model speed
and the desired propeller loading (propeller speed) are determined before starting
the experiment in order to predict the final result for the propulsion point. In this
experiment, model speed is set at 4.62 knots and the runs are repeated four times
at constant but at different loadings.
4.2 Propeller speed (load) determination
Firstly the model resistance, Rm at corresponding speed (in our case 16
knots for prototype) is obtained from resistance test results of the model. From the
interpolation, the model resistance Rm is known to be 72.5 N.
Table 4.1: Values for Interpolation Of Model Resistance
In the first run, the propeller speed, n is set so that T<R m to simulate the
“under propelled” condition. In the second run, the propeller speed, n is set so that
T≈Rm to simulate the approximate “self propelled” condition. In the third and
forth runs, the propeller speed, n is set so that T>R m to simulate the “over
propelled” condition.
Anyhow, the Rm should be in between of minimum thrust (lowest propeller
speed set) and maximum thrust (highest propeller speed set). Hence, try and error
calculations should be done to obtain the 4 required propeller speeds from the
open water diagram.
Figure 4.1: Sample Calculation of Determining Thrust.
5.0 PROCEDURES
The procedures for determining self-propulsion point of the model at given
conditions are as follow:
i. The ship model is prepared and ballasted corresponding to the required
conditions to achieve the required draught and trim.
ii. Swing table is used to achieve required VCG and LCG.
iii. The hull model is equipped with propeller, electric motor and
dynamometer to allow the measurements of thrust (T), torque (Q) and
propeller speed (n).
iv. The ship model is transferred to the towing tank by using overhead crane.
v. The ship model is positioned to the center of the towing tank and attached
to the towing carriage.
vi. Force transducer is then attached to the ship model to allow the
measurement of force induced, (T-R). The overall setup is shown as
follow:
Figure 5.1: Overall Setup for Self-Propulsion Test
vii. Load varying method is used with a total of 4 runs available at constant
model speed.
viii. In the 4 runs, propeller speed, n (load) is varied from a low value (T<R,
model “under propelled”) through a value of self propulsion (T=R, model
“self propelled”) to a high value (T>R, model “over propelled”).
ix. For each of the run, corresponding torque, thrust, rate of rotation, speed of
hull and carriage transducer force, (T-R) are recorded.
