With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The present study proposed the concept of an offshore aquaculture system with an automated feeding platform. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the cultured fish is starved during a few days before and after typhoon attack since the feeding ship is not able to approach the offshore sea cages, which is submerged every time around 10m below the sea surface to escape from high waves and strong currents. The automated feeding system should be therefore developed to enable the cultured fish to grow faster under the severe natural condition. The proposed system consists of several submerged fish cages and a feeding platform, which includes fuel tanks, feed storage silos, and an automated feeding machine. The feeding platform was designed by numerical analysis and tank model test in order to suppress its motion as small as possible. The motion of the feeding platform was first predicted by numerical analysis. The unmoved point was formed at each period of the incident wave. It moves upward as the period of the incident wave increases. Consequently, the point at 8m below the sea surface (3m above the bottom of the feeding platform) is the best one to attach the feeding hose. As a result of tank model test, pitch and heave motions of the feeding platform were dominant in the waves with short (1.5 seconds) and long (3.1 seconds) periods, respectively. An unmoved point was observed on the surface of the feeding platform as predicted by the numerical model, while the top of the feeding platform moved more largely. The unmoved point for the feeding hose was specified at above the bottom of the feeding platform.

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