Rollers are made up of two parts, which moves relative to each other. One of the parts can be a fixed body, firmly mounted or kept in place by a gyro, and the other part can be the housing of the device or its float. Most of the energy loss in these devices is due to friction. The impact devices are generally constructed to use a very narrow spectre of energy frequencies. In the energy transformation of the device a part of both the kinetic and potential energy will be lost due to the uneven pulsating character of the energy delivery whether the uptake takes place on a firm body or a flexible body.
Eaters use both potential and kinetic energy.
The limitations on the possible energy extraction are very dependable on the design. Both devices for wash up and flush in will lose most energy to energy as friction. Principally eaters can be scaled to fit any size of wave, which does not apply to the movers .