On the Capsizing Process of a Fishing Veseel in Breaking Waves

Abstract

The authors already examined the ship capsizing in irregular waves probabilistically, but the capsizing in relatively large breaking waves was left un-examined. This is because that the controll of occurence of breaking wave is difficult inirregular waves. So,in this paper, we investigated the ship capsizing process (fishing vessel of 300 ton class) deterministially in deterministic breaking waves by adopting the so called concentration phenomena of Transient Water Waves. Here we used newly introduced remote sensing technique (position Sensor Device, P.S.D) by Prof. S.Takezawa. Furthermore, to confirm our experimental technique, we conducted a digital simulation by introducing an equation of motion which can describe the capsizing including sway, roll and heave mode. In this simulation, as external force, we mainly considered Froude-Krylov force from linear velocity potential of Transient Water Wave by integrating pressure along the ship surface up to the crossing points with wave surface of finite elevation. On the other hand, the breaking wave effect was represented by adding a pulse like force on the ship. From these experiments and simulations, the following conclusions are obtained. Namely, the minimum impact force generating capsizing, when considered as rectangular pulse, for actual ship of this study is estimated about 135ton and its duration is about 1.0 sec with wave height of about 7.5m. Time to complete capsize is about 10 sec. Furthermore, the direction of this impact force is about 25 degrees upwards, the net mass of impact water is about 210ton and the speed of breaking wave front is about 16m/sec. Finally it was shown that the boundary values, like impact strength and GM etc, generating capsizing seems to be estimated using this simulation.