Academics – Naval Architecture : 2022/JUL/08
Question
Q8) A model propeller of 0.45 m diameter and 0.95 pitch ratio, is tested in fresh water of density 1000 kg/m3, at a constant speed of advance of 1.4 m/s.
The thrust and torque values for a range of rotational speeds are given in Table Q8.
| Revs/s | 4.25 | 4.50 | 4.75 | 5.00 | 5.25 |
| Thrust(N) | 34.5 | 50.6 | 69.0 | 89.2 | 110.0 |
| Torque(Nm) | 2.63 | 3.60 | 4.62 | 5.68 | 6.72 |
Table Q8
(a) Draw curves of propeller efficiency and delivered power against a base of real slip ratio for the model propeller. (9)
(b) Using the curves drawn in Q8(a), determine EACH of the following:
(i) The model propeller rotational speed for maximum efficiency; (4)
(ii) The delivered power for a geometrically similar ship’s propeller of 6 m diameter, operating in sea water of density 1025 kg/m3 at a real slip ratio of 0.34, given that delivered power is proportional to (diameter)3.5.
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