Question 55 OSE02 - Assistant Engineer - OSV

The Correct Answer is C ### Explanation of Why Option C is Correct Option C states: "The manual shutdown lever is operated by means of a remote pull cable and uses the over speed trip mechanism to accomplish engine shutdown." This statement accurately describes the common design and function of emergency or manual shutdown systems on large marine diesel engines, particularly those used in anchor handling supply vessels (AHTS). 1. **Operation via Remote Pull Cable:** In an emergency, personnel often need to shut down the engine quickly and safely from a location away from the hot, noisy, or potentially hazardous engine block itself (e.g., from the control platform, outside the engine enclosure, or a dedicated emergency station). This remote access is facilitated by a flexible pull cable (or sometimes hydraulics/pneumatics) connected to the engine's shutdown mechanism. 2. **Utilizing the Overspeed Trip Mechanism:** For a true, immediate, and reliable emergency stop, the engine needs to be cut off from fuel completely and instantaneously, regardless of the governor position. The overspeed trip mechanism is designed precisely for this purpose—to slam shut the fuel racks or injection pump fuel supply immediately. When the manual emergency shutdown is activated (via the remote pull cable), it is typically routed to mechanically activate the same mechanism that the overspeed device uses, ensuring a rapid and positive engine stop. ### Explanation of Why Other Options Are Incorrect **A) The manual shutdown lever is operated by means of the over speed trip reset lever and uses the over speed trip mechanism to accomplish engine shutdown.** This is incorrect because operating the shutdown lever is not the same as operating the *reset* lever. The reset lever is used to return the trip mechanism to the operational state *after* a shutdown (either an overspeed event or a manual trip). Furthermore, the primary manual operation is via a pull cable, not typically directly through the reset lever itself. **B) The manual shutdown lever is operated by means of a remote pull cable and uses the governor fuel control linkage to accomplish engine shutdown.** This is incorrect for an **emergency/manual shutdown**. While the governor controls the fuel linkage for normal speed regulation, relying on the governor linkage for an emergency shutdown is unreliable. The governor might be sluggish, stuck, or fail to achieve the rapid, positive "zero fuel" required for emergency stopping. Emergency stops are designed to bypass the normal governor control and utilize the dedicated, highly reliable overspeed trip mechanism for instantaneous fuel cutoff. **D) The manual shutdown lever is operated by means of the emergency trip reset lever and uses the governor fuel control linkage.** This is incorrect on two counts: 1. It confuses the shutdown operation with the *reset* operation (similar to Option A). 2. It incorrectly states that the shutdown uses the governor fuel control linkage (similar to Option B), which is not the standard procedure for a positive emergency stop.