Question 58 1AE01 - First Assistant Engineer

The Correct Answer is B ### Explanation for Option B (Controllable-pitch propeller) A controllable-pitch propeller (CPP) is generally used in ships where the main engine or prime mover (often a diesel engine or gas turbine) must run at a constant, optimized speed. This constant speed is crucial because it is needed to consistently drive the attached **shaft-driven generators**, ensuring they maintain a stable AC frequency (e.g., 60 Hz or 50 Hz) for the ship's electrical grid. With a CPP, the vessel's speed and direction (ahead/astern) are controlled entirely by changing the pitch (the angle of the blades relative to the water) while the engine and shaft maintain a constant RPM. This allows for excellent maneuverability and efficient power generation simultaneously. ### Explanation of Incorrect Options **A) Fixed-pitch propeller (FPP):** An FPP requires the engine speed (RPM) to change drastically for maneuvering or speed control. If an FPP were used, the engine driving the propeller would constantly change speed, making it impossible to maintain a stable, constant frequency for the attached shaft-driven generator. **C) Tandem propellers:** Tandem propellers are a configuration detail (two propellers on the same shaft or two parallel shafts) used to manage high power loads or optimize efficiency, but they do not define the mechanism for thrust control. They could be FPP or CPP, but the tandem arrangement itself does not solve the constant-RPM requirement. **D) Detachable-blade (built-up) propeller:** This is a type of construction design where the blades are bolted onto the hub (a type of FPP). Like all fixed-pitch designs, it requires the engine RPM to change for speed control, making it unsuitable for driving constant-frequency generators.