Abstract: An apparatus for harnessing the energy derived from the undulatory motion of a body of water includes an assembly having a buoyancy sufficient for maintaining it afloat in the water, a first structure substantially following multidirectional undulatory motions of the water and a second structure mounted in the assembly for free movement in a plurality of planes with respect to the first structure. The second structure is displaceable by gravity and by forces derived from the motions of said first structure. There is further provided a device connected to the first and second structures for generating a pressure output in response to the force derived from the relative motions between the first and second structures. An arrangement is coupled to the pressure output of the device for utilizing, at least indirectly, the energy derived from the pressure output.