During maneuvering operations for a direct reversing large, low-speed, main propulsion diesel engine, which of the following actions is used to stop the shaft from turning prior to changing the engine rotation for a vessel with moderate headway?
• Direct-reversing, low-speed diesel engines and how they change rotation • What actually slows or stops the propeller shaft when the vessel still has headway • Difference between engine-side forces (air, lubrication, flywheel) and hydrodynamic forces on the hull and propeller
• When the ship has moderate headway, what is physically resisting the propeller’s rotation as you try to stop or reverse the engine? • Which option represents a natural effect rather than an active control or adjustment by the engineer? • Which choices directly affect engine internal operation, and which affect the propeller through the ship’s motion in the water?
• Identify which options are engine control actions (things you do in the engine room) versus natural physical effects. • Consider how a freewheeling propeller behaves when the ship is still moving through the water but the engine is being brought to a stop. • Ask: Before you can admit reversing air, what must already have happened to the shaft, and what helps that happen when the vessel still has forward speed?
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