Question 34 OSE01 - Chief Engineer - OSV

The Correct Answer is C **Explanation for Option C (Correct Answer):** The described scenario—cyclic, rhythmic variations in engine speed (often called "hunting" or "surging") occurring at steady load, which immediately stop when the governor is manually blocked—is the classic symptom of an unstable governing system. This instability means the governor is overcorrecting for small speed changes, leading to a continuous oscillation. In hydraulic governors (like those typically used on marine diesels), stability is maintained by a temporary feedback mechanism called the **compensating system** (or speed droop mechanism). The **compensating needle valve** controls the rate at which oil is allowed to leak out of the compensating system's buffer spring and dashpot assembly. * If the needle valve is too far open, the compensating pressure dissipates too quickly, leading to **under-damping**, causing the governor to hunt (oscillate). * Adjusting (partially closing) the compensating needle valve increases the damping effect, stabilizing the governor's response and eliminating the hunting behavior. **Why the other options are incorrect:** * **A) Replace the fuel injector nozzle of the misfiring cylinder:** A misfiring cylinder causes irregular speed variations, smoke, and loss of power, but it would not typically cause the highly rhythmic, cyclic hunting that immediately stops when the governor is disconnected. If the issue were related to fuel supply in a cylinder, blocking the governor linkage would likely still leave a noticeable irregularity, but the rhythmic hunting is purely a governor instability issue. * **B) Tighten the bolts securing the governor base to the engine:** Loose mounting bolts would cause vibration and potentially imprecise movement of the linkage, but the primary symptom of hunting (rhythmic oscillation that ceases when the governor is blocked) specifically points to an internal hydraulic instability, not external mounting issues. * **D) Replace the governor drive gears:** Worn or damaged drive gears would likely cause excessive noise, mechanical backlash, or irregular speed variations, but they would not cause the classic, high-frequency, rhythmic hunting associated with inadequate hydraulic compensation (damping).