A Study on Hull Deflection and Shaft Alignment Interaction in VLCC

Abstract

Modern ship hulls of large oil carriers and container carriers have become more flexible with scantling optimization and increase in ship length. On the other hand, as the demand for power has increased with the ship size, shaft diameters have become larger and stiffer. Consequently, the alignment of the propulsion system has become more sensitive to hull girder deflections, resulting in difficulties in analyzing the alignment and conducting the alignment procedure. Accordingly, the frequency of shaft alignment related bearing damages has increased significantly in recent years. The alignment related damages are mostly attributed to inadequate analyses, changes in the design of the vessel, shipyards' practices in conducting the alignment, and a lack of well defined analytical criteria. The hull deflections should be considered at the design stage to minimize the bearing damage caused by hull deflection. Hull deflections can be estimated by analytical approach and reverse calculation using the measured data. The hull girder deflection analysis using the reverse calculation will be introduced in this paper.