Abstract
For the hydrofoil craft, motional performance is an important factor to the operation of the craft. As it is well known that the hydrofoil configuration can be divided into two general classifications. One is a surface piercing type and the other is a fully submerged type. Now the fully submerged type is the main current in the hydrofoil craft due to the performance of the seakeeping and of the propulsion. But there is a weakness in the craft with fully submerged foils. That is, the craft itself is not so stable in motion as compared to the one with surface piercing foils. And so it is carefully designed to determine both the principal dimension of the craft and the system of the controll apparatus. In this paper the longitudinal motion of the craft with fully submerged foils is dealt. First, it is investigated how the principal dimension such as the position of the foil installation or of the center of gravity affects to the inherent stability, and the guide to the determination of principal dimension is shown in a view point of the inherent stability. It is desirable to keep the craft itself in the stable condition when they are manually controlled. Next, the robustness of the control system for the longitudinal motion is researched, that is, it is important for the control system whether the controllability is kept or not when the characteristics of the craft on the longitudinal motion is varied from some causes. It is shown that the robustness can be well kept if the control system is designed with the optimal regulator theory.
