Question - Why Wear Down In Main Bearings Is Critical To The Condition Of The Crankshaft And Propeller Shaft System On Ships ?
Answer -
The operational stresses present within the crankshaft is influenced by the bending stresses present. If the crankshaft alignment is completely straight then the bending stresses are minimal, but should uneven main bearing wear down occur, then these bending stresses will greatly increase.
When the main bearings wear down, the alignment of the crankshaft to the propeller shaft will change. This wear down will increase the bending stress on the propeller shaft, and the external moment at the engine / shaft interface, increasing the crankshaft stresses.
When the crankshaft is subjected to these high stresses, the small defects present within the shaft could develop and propagate into cracks that could lead to shaft failure.