Hydrodynamic performance of a semi-submersible offshore fish farm with a single point mooring system in pure waves and current

•A safe and reliable mooring form of the offshore fish farm is proposed.•The mooring force and motion response of the fish farm in waves and current are investigated.•Raising the fish farm by adjusting its drought is beneficial for reducing the mooring force to further secure the fish farm in severe sea conditions.•The offshore farm is proved to have a good adaptability for cultured fish through field test of fish farming. A physical model of a semi-submersible offshore fish farm with a scale of 1:30 has been tested in a wave-current tank. The mooring force of the fish farm in waves was measured and compared for different single-point mooring arrangements, and henceforth, a safe and reliable mooring form is chosen as the mooring system for the fish farm. On this basis, the tested results for the mooring force, heave, pitch and roll of the fish farm in waves and current are presented, in which the effect of drought was discussed. The performance of blocking water flow for the fish farm in pure current was also evaluated. It has been found that increasing the anchor chain length and adding a sinker suspending from the chain could reduce the mooring force significantly despite the fluctuations in the mooring force. During the experiments, the tested value for the heave and pitch as well as the roll has been small, which indicates that the fish farm has a good stability. The mooring force has become larger, while the heave became smaller as the drought increased. Furthermore, the current velocity inside the fish farm is significantly lower than that of its outside. According to the field test results obtained in the fish farm, the farm exhibited good adaptability and it formed a suitable environment for growing cultured fish.