Concerning main propulsion reduction gears, what statement is true?

Correct Answer: Option A — The reduction gear allows the prime mover to rotate efficiently at relatively high speed and low torque and allows the propeller to rotate efficiently at relatively low speed and high torque.

Prime movers like turbines or high-speed diesels operate most efficiently at high rotational speeds with lower torque. Propellers, however, require high torque at lower speeds for efficient thrust production. Reduction gears act as mechanical transformers, matching these disparate speed and torque characteristics to optimize overall propulsion system efficiency.