Hotel Service Unit 20 Other subjects Q6 Answer

6.(a) State SIX advantages of controllabe pitch propellers.(6)
(b) State FOUR disadvantages of controllable pitch propellers.(4)

(a) Six Advantages of Controllable Pitch Propellers (6 marks)

  1. Improved manoeuvrability – pitch can be altered instantly, giving better control when docking or in confined waters.
  2. Rapid reversal of thrust – ahead to astern without stopping or reversing the main engine.
  3. Efficient engine operation – main engine can run at near constant optimum speed, improving fuel efficiency.
  4. Flexible power distribution – propeller load can be adjusted to suit varying conditions (e.g. ballast, laden, heavy seas).
  5. Reduced wear on machinery – smooth speed and thrust changes reduce stress on engine and shafting.
  6. Emergency control – propeller pitch can provide astern movement even if main engine cannot be reversed.

(b) Four Disadvantages of Controllable Pitch Propellers (4 marks)

  1. Complexity – more moving parts (pitch control mechanism, hydraulic system) compared to fixed pitch.
  2. Higher initial cost – expensive to design, manufacture, and install.
  3. Maintenance requirements – hydraulic systems, seals, and pitch mechanism require regular inspection and servicing.
  4. Risk of failure/leakage – hydraulic oil leaks or pitch control malfunction may lead to loss of propulsion or pollution risk.