Because most wave motion occurs at the sea surface, the buoy rises and falls with the waves, but the plate, 30 meters (100 feet) down, remains relatively stationary. Between the surface buoy and the metal plate is a large hydraulic cylinder with a piston inside. As the buoy rises and falls, it pushes and pulls on this piston. This forces hydraulic fluid through a hydraulic motor, which in turn runs an electrical generator.

One of the first challenges the team faced was figuring out the best way to convert the vertical motion of the waves into rotary motion that could power a generator. First they bought a custom-made generator from an outside company, but that turned out to be too inefficient to be useful. Going back to the drawing board, the team designed their own system using an off-the-shelf hydraulic motor similar to those used on earth-moving equipment and on MBARI’s underwater robots. These hydraulic motors use moving hydraulic fluid to drive a rotating shaft with up to 95 percent efficiency.

Another challenge that Hamilton’s team faced was designing a mechanism that would return the piston to its starting point after a wave had passed. Hamilton initially envisioned using a large metal spring for this purpose, but the metal spring turned out to be much too heavy. So the team redesigned the system to incorporate a pneumatic spring—a chamber filled with nitrogen gas, and mounted at one end of the piston. As the piston moves with the waves, it compresses or decompresses the nitrogen gas in the chamber. After the wave passes, the gas in the chamber returns to its original pressure, forcing the piston back to the middle of its stroke.