Effects of hull shape and launching conditions on the behaviors of free-fall lifeboats after water entry

Abstract

In the research and development of free-fall lifeboat systems, emphasis has been mainly on the performance confirmation tests using full-scale prototype boats. On the other hand, fundamental studies that illustrate the behaviors of free-fall lifeboats during water approach and entry have not been sufficiently carried out. The purpose of this paper is to show the effectiveness of a numerical simulation method in evaluating quantitatively the effects of hull shape and launching conditions on the behaviors of free-fall lifeboats. Two lifeboat models having different hull shape, weight distribution, moment of inertia, etc., are utilized in a series of model experiments. Computed results such as boat motion and impact acceleration on the hull are compared with measured ones, and the comparison confirms the validity of our numerical method. The marked effect of guide rail length on boat motion and acceleration are also illustrated. In the case of a boat with an extreme transom stern, it is found that an impulsive force is exerted on the stern during the run of the boat below the water surface. A sharp bow, shown herein, is effective for smooth evacuation motion.