Recently, several propulsion shafting damage incidents have been reported. They are generally said to be related to improper shafting alignments that fail to absorb changes in bearing offset between different operating conditions. Such damage tends to occur on ships with large draft variations from ballast to fully loaded conditions, such as VLCCs. In this paper, the authors propose a new enhanced method for propulsion shafting alignment taking into account variations in bearing offsets while in service, based on the results of onboard ship measurements and FE analysis carried out to determine the hull deflection between different conditions. Although the results show that static hull deflection arising from changes in draft can be predicted by FEM with satisfactory accuracy, a significant dynamic deflection component thought to be related to ship motions in waves, and difficult to predict by analysis, is also present. In addition to checking the effect of predetermined full deflection, high accuracy alignment calculation models incorporating all engine bearings and using equivalent circular bar representing crankshaft, and an optimisation procedure to minimise shafting sensitivity to bearing offsets variation are proposed.
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