Lift Characteristics of Controlling Fins of Resonance-Free SWATH

Speed reduction, additional resistance or slamming, which caused by the large ship motions, should be avoided for a high-speed oceangoing vessel, because of the delivery punctuality and high value of the cargo. A promising ship type for such the oceangoing vessel is the so-called “Resonance-Free SWATH (RFS)”. It has negative restoring moment due to the extraordinary small water plane area. As a consequence, the resonance peak is removed from the motion response. RFS is designed to cross 4,800 nautical miles of Pacific Ocean within 5 days punctually at a speed of 40 knots, with good seaworthiness such as no speed reduction or absolutely no slamming even when running in the rough sea of sea state 7 with significant wave height of 6–9 m.The attitude of RFS with negative restoring moment is adjusted by four pairs of controlling fins attached to the fore and aft ends of lower hulls. In the previous works, the quasi-steady values of lift-curve slope are usually adopted in the motion equations of frequency domain. However, when working in waves, the controlling fins are not in a steady state. The lift coefficient is no longer a constant. In addition, there exist a phase lag between the movement of attack angle and the fin-generated lift.The theoretical prediction and the experiment to analyze the phenomena of lift generation including the phase difference and the interaction among fins and lower hulls are carried out. The results show that the characteristics of fins depend on the encounter frequency. Then, the effect of lift characteristics of controlling fins on the RFS model is discussed. The results of theoretical estimation and experiment are discussed and it is observed that estimated results agree to some extent with experimental results.© 2014 ASME