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)

Answer 1

Part (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.

Vibration:

Uneven cavitation across the blades leads to imbalanced forces, causing vibrations in the propeller and the ship.
These vibrations can reduce the comfort of passengers and crew and stress the ship's structural components.

Noise:

The collapse of vapor bubbles generates loud noise, which can interfere with onboard communication and underwater sonar systems.
This noise is a significant concern for naval vessels and marine life.

Reduced Performance:

Cavitation reduces the efficiency of the propeller by causing loss of thrust and torque.
The presence of cavitation decreases the propeller’s ability to convert rotational energy into forward motion, lowering the ship's speed and increasing fuel consumption.

✓ Verified Model Answer (Text Solution)

Effect of cavitation on propeller blades: