It can be considered that the Twin-Hulled Air Cushion Vehicle is a promising marine vehicle because it has wide deck area and good stability as a catamaran ship and also it has an excellent high speed performance as an air cushion vehicle. A summary of the theoretical and experimental studies on the resistance characteristics of the Twin-Hulled ACV is shown as follows. (1) The method of calculation proposed in this paper was confirmed by the experimental results. (2) It was recognized that the mathematical model used in this paper was applicable to actual ship forms with a speed exceeding FROUDE number 0.40. (3) The interaction between twin hulls and cushion pressure may reduce their total wave resistance. (4) It certainly is possible that the optimum design of Twin-Hulled ACV in the relation with the cushion pressure distribution and the distance between twin hulls, reduces even the total resistance due to the reduction in the wetted surface area of the twin hulls. The theoretical results show that an optimum combination, which makes the total resistance minimum, exists for the distance between twin hulls at Fn=0.40.
An explanation of the drag characteristics of a Sidewall Air Cushion Vehicle is proposed based on the towing tank tests of an ACV model. The simple model with the flat plate sidewalls has been chosen so that the measured drag can be easity broken down into its components. It is found that the trim of a craft plays a remarkable role in the drag reduction, as well as the cushion pressure which was forcused on our first report. The trim depends on the both wave gattern which is formed by the cushion pressure, and also the additional moment which is adjusted by the ballast and the tbrust line. It is shown that the trim exerts primarily skirt drag and indirectly wave pattern drag. Namely, inadequate trim causes the scooping action by the rear skirts which results in increase of skirt drag at the secondary hump speed (Fu=0.38). When the scooping action by rear skirts is observed, wave pattern drag is reduced relatively, because wave is broken down. The mechanism of drag reduction due to trim adjustment can be explained by the interaction of these factors. The wetting area of sidewalls and skirt drag depend on FROUD Number, cushion pressure, sidewall depth, cushion air gap and trim. The estimation of the wetting area and skirt drag is reached according to experimental data.