An energy conversion system includes a power takeoff system, a fin connected to the power takeoff system, and a control system on board the fin. The fin is submerged below a surface of the sea, and the fin is configured to use subsurface wave motions to extract energy.

A wave energy converter apparatus comprising a floatable wave receiver unit with first and second chambers that extend and retract in response to wave motion, a power conversion and generation module disposed on a float unit that floats in the body of water and a connection assembly connecting the wave receiver unit to the power conversion and generation module. The second chamber includes an open front end to hold the first chamber, allowing partial horizontal axial movement. The assembly includes a hydraulic cylinder and a connecting structure that transfer wave motion energy to the cylinder. As the first chamber moves forward into the second chamber, the hydraulic fluid in the cylinder becomes pressurized. The pressurized fluid powers the hydraulic motor, which in turn drives the generator. A flexible corrugated shield surrounds the side panels of both chambers to prevent water entry.