Experimental Study on Behavior of Drifting Boats Due to Tsunami and Their Collision Forces

There are high possibilities in the near future that great earthquakes occur and large-scale tsunamis attack Japan. In fishing ports facing on the ocean where a large number of fishing boats are moored, these boats would be littered in the ports, or drifting boats would collide with back-yard-structures, if such a tsunami attacks, like an event actually happened at Hokkaido in 1993. This is one of major concerns for tsunami countermeasures in fishing ports. To predict and reduce these damages, it is absolutely indispensable to know the behavior of drifting boats and their collision forces. In the present study, hydraulic experiment was performed to investigate behavior of a boat and collision forces, as well as properties of tsunami. Based on a series of experiments, it is revealed that boats tend to be drifted keeping initial angle. Moreover, under higher incident wave conditions, the drifting velocity is influenced by the initial direction of boats than the height of draft.