The ocean-current generator we're planning to build would float 100 to 200 feet below the sea surface. The device is a 65-foot-diameter cylinder shaped to speed up water flow, with propeller blades attached to its frame. As water flows through, it strikes the blades and spins a rotor, which generates electricity. A 17-foot center opening would allow animals to pass through unharmed. We estimate that in the Gulf Stream, a few miles offshore from West Palm Beach, Florida, the five-knot current would turn the blades about eight times per minute, generating about a megawatt of power.