Question 27 OSE01 - Chief Engineer - OSV

The Correct Answer is D **Explanation for Option D (Correct Answer):** The situation described involves unusual screeching noises specifically when transitioning from one direction (e.g., ahead) to the opposite direction (astern) using Airflex pneumatic tire-type friction clutches within a reversing reduction gearbox. Airflex clutches rely on compressed air to engage and disengage. When changing direction, the procedure (whether controlled manually or automatically via the bridge control system) requires sequential steps: 1. **Disengagement of the initial clutch (Ahead).** 2. **Neutral period (Engine idling, shaft slowing down).** 3. **Engagement of the opposite clutch (Astern).** The screeching noise indicates that the new clutch (Astern) is being engaged while the shaft is still rotating significantly in the original direction (Ahead), meaning the clutch is slipping excessively as it attempts to rapidly overcome the rotational inertia of the shaft and propeller. If the Engine Order Telegraph (EOT) handle is moved too quickly through the neutral position and into the opposite direction (Astern Idle), the system does not allow enough time for the propeller shaft to slow down to a standstill (or near standstill). This insufficient dwell time in neutral means the Astern clutch engages while the shaft is still spinning, causing severe friction, heat, and the resulting screeching sound due to heavy slip, which is characteristic of "shock loading" or insufficient time for shaft reversal preparations. **Why the Other Options Are Incorrect:** * **A) The EOT handle is being left in neutral and then in astern idle for too long a period of time.** * *Incorrect.* Leaving the handle in neutral for *too long* allows the shaft ample time to slow down, ensuring the new clutch engages smoothly with minimal slip, thus preventing screeching. * **B) The EOT handle is being left in ahead idle and then in neutral for too long a period of time.** * *Incorrect.* Excessive time spent in the initial directional idle (Ahead Idle) before moving to neutral is irrelevant to the screeching occurring *during* the directional transition (engagement of the Astern clutch). A long dwell in neutral would still follow, ensuring a smooth transition. * **C) The EOT handle is being left in ahead idle and then in neutral for too short a period of time.** * *Incorrect.* While moving quickly from Ahead Idle to Neutral (or any step in the process) can lead to problems, the critical phase for screeching is the engagement of the *new* clutch (Astern). A short period in neutral means the Astern clutch engages while the shaft is still spinning quickly, which confirms the diagnosis, but the precise description of the error related to the transition speed is best captured by option D: the entire period allowed for deceleration (Neutral time) and subsequent engagement (Astern Idle) was too short. Option D focuses directly on the sequence (Neutral to Astern Idle) that causes the damaging engagement slip.