Abstract: An apparatus designed to float on or in a liquid has at least two buoyant members. The apparatus utilizes relative motion between the buoyant members to generate power, and the buoyant members are coupled to the apparatus in such a manner that surface movement of a fluid that the apparatus is floating in causes relative motion between the buoyant members. The apparatus may be a housing that includes an electrical apparatus within it, with the electrical apparatus being powered directly or indirectly by power generated by the floating apparatus. The apparatus may be a sonobuoy, and may include a sensor array hanging from a floating housing that includes the at least two buoyant members.