Shaft alignment of large LNG carrier with twin screw propulsion

Abstract

Optimized shaft alignment and high-quality construction are important guarantee of safe operation for propulsion system on board. Twin-propulsion system arrangement with certain degree skeg is more and more adopted by large LNG carrier. The global FE model with local refined mesh was used to capture the deflection of the hull structure around the propeller shaft system under different draft and loading conditions. Propeller forces were analyzed by computational fluid dynamic under severe operational conditions. Ship hull deformation and propeller forces were considered during the shaft line alignment calculations. In shaft line alignment calculation, there were five static loading conditions and six dynamic loading conditions. Following an iterative procedure in DNV shaft alignment software, the vertical position of all bearings relative to reference line was obtained in all calculated loading conditions. A stern tube bearing monitoring system was installed to monitor alignment performance in real time.