Troubles by the dam age of the shafting of main propulsion system give a great impact on the safety of vessels as well as the budget of ship's owners with its tendency of ceaselessness. Cause of trouble varies widely and identification of itrequires huge efforts and long time in many cases.The trouble case introduced hereunder also forced the vessel about two-month downtime for repair work and about six-month investigation by the ship builder and the engine manufacturer etc.Estimated cause of trouble obtained is as follows:Original design of shaft alignment was rather less flexible.Deformation of hull structure from the warming of engine (cool condition→warm condition) and change of Ship's condition (light condition→laden condition).Original design of shaft alignment was based on the cool and light condition.The journal of No.8 main bearing got afloat reclining down aftward and too high oil pressure generated at the aft edge of the lower bearing metal, which load to the metal fracture and heat crack of crankshaft. Unknown factors are still left, yet for theprevention of recurrence of similar trouble as many lessons as possible must be learned from this accident and close cooperation of parties concerned including ship owners, ship builders and engine manufactures is strongly required.
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