Abstract: A very small one-man hydrofoil craft was developed and the rolling motion and maneuverability of this boat were measured and compared with the numerical simulation. The boat is 5.8m long and weighs 150 kgf including one crew. The hydrofoil system is canard type consisted of fully submerged foils. The pitching motion is controlled automatically by a height control mechanism attached to the fore foil. On the other hand, for the rolling motion, the boat has no automatic control system. The crew maintains lateral stability by controlling rudder angle and shifting his weight in the cockpit just as controlling a bicycle. In order to clarify the lateral stability mechanism of this craft, sea tests were performed to measure the motion of the boat, rudder angle and attitude of the crew. Then numerical simulation was performed considering the motion of the boat such as surge, sway, yaw and roll. Simulated results agreed well with the measured data.

　

 Since 1994, a filly submerged hydrofoil system has been employed to a solar boat at the Kanazawa Institute of Technology in order to attain high speed [1,2,3]. For the research of control mechanism for these very small hydrofoil crafts, we built a testing boat, which is 5.8m long and weighs 150 kgf including one crew. The hydrofoil system is canard type consisted of a main foil carrying approx. 80% of the weight and a fore foil carrying remains. Because the boat is small and the speed is not so high, such as 5m/s to 10m/s, the control system for the foil born cruising is very simple. The pitching motion is controlled automatically by a height control mechanism attached to the fore foil. On the other hand, for the rolling motion, the boat has no automatic control system. The crew maintains lateral stability by controlling rudder angle and shifting his weight in the cockpit just as controlling a bicycle.

　

 The first hydrofoil boat with this concept was developed by Horiuchi in 1955 [4]. He built and tested his boat, and indicated that the boat had sufficient stability and high-speed performance. In 1994, Terao applied this concept to his solar boat successfully, and also analyzed the dynamic stability of the boat [5]. However, in these works, the measurement of motion of the boat was not indicated. In this report, in order to clarify the lateral stability mechanism of this small hydrofoil craft, sea tests were performed to measure the motion of the boat, rudder angle and attitude of the crew. Then numerical simulation was performed to compare with the measured motion of the boat.

　

2.1 Specifications of Boat

　

 The boat configuration and principal dimensions are shown in Figure 1 and Table 1. The boat is 5.8m long and weighs 150kgf including one crew. The boat is constructed as a sandwich structure of carbon fiber reinforced plastic (CFRP) with a polyvinyl foam core. The propeller is driven by DC motors powered by batteries connected in series as 24V. The contra rotating propeller is adopted in order to cancel the propeller torque, which affects lateral stability of the boat at foil born cruising. The cruising speed is 7 to 8m/s in power consumption of 2 to 3kw. Two small outriggers are attached to the main hull to prevent capsize by the rolling accident at foil born cruising.

　

 The hydrofoil system is canard type consisted of fully submerged foils. A main foil carries approx. 80% of the weight and a fore foil remains. The specifications of the main and fore foils are shown in Figure 2 and Table 2. These foils are made of CFRP. Both main and fore foils are set in horizontally and connected with the hull using struts. The strut for the main foil is fixed on the hull and the chord length is 110mm. A drive shaft of the power train goes through inside of the strut and the propeller is attached at the bottom of it. On the other hand, the strut for the fore foil is able to rotate around a vertical shaft and works as a rudder. The crew controls the rudder with a foot pedal which is connected with the rudder shaft by wire. The chord length of the fore strut is 45 mm. Although the main foil is connected with the strut tightly, the fore foil is connected movable and able to change the attack angle. The control system of the attack angle is mentioned in the following section.