Question 20 1AE01 - First Assistant Engineer

The Correct Answer is D **Explanation for why Option D is correct:** An **isochronous governor** is defined as a governor that maintains the engine speed (RPM) at exactly the same set point regardless of the load applied, meaning the droop is zero (0%). In the context of electrical power generation, particularly on a ship's service alternator (generator), the primary requirement is to maintain a constant electrical frequency (typically 50 Hz or 60 Hz). Since frequency is directly proportional to the generator's rotational speed, an engine driving an alternator must maintain a precise, constant RPM. Isochronous operation is essential for standalone generators or when generators are running in parallel to ensure stable system frequency, making this application the ideal use case for an isochronous governor. **Explanation for why the other options are incorrect:** * **A) An isochronous governor is ideally suited for a ship's geared propulsion drive driving through a fixed pitch propeller.** * This is incorrect. Propulsion drives typically require a **droop governor**. When an engine is used for propulsion, it needs the ability to increase torque and prevent the engine from stalling or overloading when faced with sudden changes in water resistance (e.g., heavy seas). A governor with droop allows the speed to decrease slightly as the load increases, which aids in stable load sharing (if multi-engine) and protects the engine by providing a better torque characteristic curve for maneuvering and load changes. * **B) An isochronous governor is ideally suited for a pump drive associated with maintaining a constant pump discharge pressure.** * This is incorrect. While some specialized systems might benefit from precise speed control, maintaining constant discharge pressure is often achieved more efficiently using other control mechanisms (e.g., variable speed drives or pressure relief valves) or by using a governor with some droop characteristics, especially in centrifugal pump applications where constant pressure does not necessarily equate to constant engine speed across all flow rates. Isochronous control is generally not the primary or "ideal" requirement for pressure regulation unless the pump is a specialized positive displacement type where flow must be perfectly constant. * **C) An isochronous governor is ideally suited for a ship's direct-reversible propulsion drive driving through a fixed pitch propeller.** * This is incorrect for the same reasons as Option A. Propulsion drives require governors with **droop** for stability, protection against overload, and better engine torque characteristics necessary for maneuvering and handling large, sudden load fluctuations common in heavy maritime applications.