Seaworthiness of Resonance-Free SWATH with Movable Fins as an Oceangoing Fast Ship

A “Resonance-Free SWATH (RFS)” as the oceangoing large fast ship has the negative restoring moments, which leads to resonance-free in motion responses, because of the extraordinarily small water plane area. RFS is designed to cross 4,800 nautical miles of Pacific Ocean within 5 days punctually at a high speed of 40 knots, with the good seaworthiness such as no speed reduction or absolutely no slamming even in the rough sea. To verify the seaworthiness of the RFS, experiments in model basin and theoretical predictions are carried out. In the theory of RFS’s motion controlled by PD, the time delay of fin lift generation and the interaction among fins and lower hulls of RFS are taken into account. Also, experiments using RFS model with movable fins are carried out to validate the theoretical estimation. As the result, the maximum stable gain constants for PD control of RFS’s motion are determined and motion responses of RFS are significantly reduced. Then, motion responses of RFS in regular and irregular head waves are compared with those of various hull forms, such as monohull, ordinary SWATH or trimaran. The predominance of RFS regarding seaworthiness will be pointed out in the conclusion.