Abstract: The patent describes a device intended to both attenuate water waves efficiently, and efficiently convert the attenuated energy to useful energy, while having minimal negative environmental impact. The device consists of a flexible slab that rests upon a rigid but permeable horizontal plane between surface and bottom. The slab is alternatively pushed away from the plane, and alternatively it is pressing hard on the plane. The resulting force may be converted to hydraulic energy using established technology. The critical parameters are the submerged weight per area and elasticity of the slab, equations for which are given in the patent.