A platform-like device for generating electricity from moving fluids has at least two fluid turbines coupled to one another through a frame. The fluid turbines are adapted to rotate in opposite directions. The fluid turbines also provide buoyancy for the platform so that the platform is self supporting in the water. The fluid turbines preferably have helicoid flights (screw-like threads) mounted to generally prolate casings. The fluid turbines preferably connect to electric generators through belt, chain-drive, or other transmission systems. The platform may additional support a wind turbine.