A rotating cylindrical float (spar buoy) is the turbine shaft of vertical axis wind turbine. Because the weight of rotor is directly supported by buoyancy, the concept is suitable for huge floating offshore wind turbine. The name of the concept is Floating Axis Wind Turbine (FAWT).
The video shows the preliminary model experiment of a small wind turbine (a variation of FAWT). It will be a mobile floating wind turbine with an umbrella like folding mechanism. The turbine supply electricity to ocean platforms. Also, it can be used as an emergency power supply in the large hazard area caused by tsunami, earthquake, etc.
The size of support floats surrounding the turbine shaft will be significantly reduced in the actual device.
Offshore WIND staff, January 21, 2014; Image: flickr