Answer Happy

A cruise ship is being designed to travel at a cruising speed of 25 knots at sea. The two sides of the ship undergoing frictional air resistance can each be assumed to be a rectangle of length 360 m equal to the ship's length and height of 20 m, while the wetted area of the hull is around 3240 m². This ship building company is also designing a new 4-bladed fixed-pitch marine propeller of 4 m diameter. In-house experiments on a small propeller model were conducted at the same Reynolds number as the cruising condition, and gave the data shown in the Figure QB2. Given: 1 knot = 0.514 m/s a) Stating any assumptions you make, determine the rotational speed of the propeller to deliver the required cruising speed. (17) b) Briefly discuss how you would improve your predictions. ( (3) 1 0.9 efficiency thrust coefficient torque coefficient 0.8 0.16 or 0.7 0.6 0.12 THAUST COEFFICIENT CT EFFICIENCY TORQUE COEFFICIENT CT 0.5 0.4 0.08 0.3 0.2 0.04 0.1 ---- 0 1.1 1.2 1.3 1.4 1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 ADVANCE RATIO J Figure QB2 Performance curves of the 4-bladed propeller for efficiency (y axis). thrust coefficient (y axis), and torque coefficient (y2 axis) against advance ratio (x axis). Note: the efficiency here is given by: J Cr/21r C.