Recently, the stiffness of designed marine propulsion shafting has been increasing remarkably according to increasing of ship’s size and the resultant increase of shaft diameters. On the other hand, hull structures have become more flexible as a result of scantling optimization and increase in ship length.
Consequently, the alignment of a propulsion shafting system has become more sensitive to hull structures. And the alignment can be misleading especially when some facts are not taken into consideration. This fact has led to the bearing damage related inadequate analysis, inadequate practices of the shipyard in conducting the alignment and a lack of defined analytical criteria.
Ideally, a shaft alignment analysis should be peformed for maximum allowable alignment tolerances, resulting in acceptable bearing reactions and misalignment angles under all operating conditions of the vessel(loaded, ballast, hot and cold) and thermal deformation of engine bed plate.
The purpose of this paper is to verify a reliable optimum shafting alignment for extra large container vessel. Therefore shafting design and installation to static and running condition for the optimal shafting installation of extra large container vessels with the long shaft would be introduced. Futhermore, considering the effects of main engine bearing's numbers and thermal deformation, the calculation was performed.
Also the results were investigated when vertical direction stiffness is considered to linear and rigid support. As a result, off-set of the long shaft was few changes, but in case of short shaft, the bearing reaction force of MB1 was possible to unload state or negative load condition (-) due to off-set's changes by elasticity. And at the installed shafting on the basis of the shafting alignment calculation process, design results were compared with the value of that by the jack-up method to measure the reaction force of each bearing in order to clarify the paper. Conclusively this vessel measured at the bearing reaction force showed that close to the design value.
But first of all, the shafting alignment process mentioned is to be carried out under the effective control on the basis of optimal design in order to derive satisfactory results in the field.
Lastly this paper introduced the shafting alignment analysis result by using programs of H classification society and shaft alignment through the eyes of the optimal design strategies was sought.