Water Entry Simulation of Free-fall Lifeboat

Abstract

Free-fall lifeboats provide significant advances in the maritime lifesaving systems. Much of the danger associated with conventional lifeboat systems can be eliminated by this new evacuation method if the boat is launched selecting suitable launching parameters. A primary consideration in the freefall lifeboat system is the acceleration field to which the occupants are subjected during water entry. The international regulation, therefore, requires that a lifeboat for free-fall launching shall be capable of ensuring protection against harmful accelerations when it is launched with its full complement of persons and equipment from at least the maximum designed height.When the lifeboat enters the water, the acceleration forces exerted upon the boat due to impact are very high. According to the basic study upon the human body response, tolerance level for acceleration is different for each axis of the human body. Therefore, the safe seats in a free-fall lifeboat are usually reclined relative to the axes of the lifeboat to reduce the effect of high accelerations. In this paper, the authors introduce a new and probably the simplest concept to evaluate the acceleration field of the free -fall lifeboat and apply it to the analysis of the safe seat orientation for the occupants. The results have been compared with those of the SRSS acceleration criteria and the dynamic response criteria, both of which are recommended by the IMO, and good agreement has been found.