Class 2 (2nd Engineer) SC&S 📅 Jan 2023

Exam Question

(a) Describe the effect of cavitations on the propeller blades (6)

(b) A ship has a constant cross-section in the form of a triangle which floats apex down in sea water. The ship is 85 m long, 12 m wide at the deck and has a depth from keel to deck of 9 m. Draw the displacement curve using 1.25 m intervals of draught from the keel to the 7.5 m waterline. From this curve obtain the Displacement in fresh water at a draught of 6.50 m. (10)

Reference Answer

(a) Effect of cavitation on propeller blades:
Erosion:
Cavitation causes the formation and collapse of vapor bubbles on the propeller blade surface.
The collapse of these bubbles produces high-pressure shockwaves and microjets that erode the blade material, leading to surface pitting and progressive damage.

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