Abstract: An improved wave motor tank utilizes a tank having an open mouth portion disposed in a downwardmost position when residing in a body of water experiencing the effects of waves and tides. The tank is coupled to a mechanical apparatus, well known in the art, utilized in extracting energy due to the fall and rise of the tank. The interior of the tank is subjected to a negative pressure so as to tightly couple the tank to the water in which it is caused to reside. The tank is provided with a flotation chamber which contains a gas thereon, offsetting the weight of the tank and any ballast attached thereto, maintaining such tank at a near weightless condition yet effectively "clamped" to the surrounding water.