Abstract: The prime-mover comprises a central inertial barge 1, a first outer wave-engaging pontoon 2 pivotally movable relative to the central barge 1 about the pivotal axis defined by the arrow A, and a second outer wave-engaging pontoon 3 pivotally movable relative to the central barge 1 about the axis defined by the arrow B. Two series of pumps 4 are mounted on the central barge 1 and driven by the pivotal movement of the outer wave-engaging pontoons 2, 3 respectively. A damping mechanism comprising two shafts 6a, 6b extend downwardly from the bage 1. The shafts 6a, 6b are provided with damping plates 7a, 7b at the bottom ends thereof. The damping plates 7a, 7b may be moved relative to the shafts 6a, 6b by being screwed up or down the shafts as required.