In the present paper, two aspects of wave energy utilization for ship propulsion or so-called “Wave Devouring Propulsion”^** are clarified.
(1) From a general viewpoint of conversion of the wave energy into the thrust, the possibility of the wave devouring propulsion is proved by considering the property of the ideal thrust generated by incoming waves and that of the drag required to propel a ship.
(2) As a realization of the wave devouring propulsion, the thrust generation by an oscillating hydrofoil advancing in waves is discussed. This problem has already been discussed by wu^{15), 16)} , but the free surface effect is not included in his theory. When the conversion of the wave power into the propulsive power is aimed at through interaction between a wave and a converter, for example, a hydrofoil, it seems to the author that the free surface effect should not be neglected, since the thrust increase due to the wave power absorption and the wave resistance increase are both proportional to the square of the wave amplitude. In the present paper, Wu's theory is improved by including the free surface effect approximately, and some numerical results are given for a non-oscillating hydorfoil advancing in waves or “A Linear Wells Turbine”.