Water energy... What?

No, we are not talking about just floating along with the current. The device on the right, a "Waterotor" is a portable turbine that generates energy from the water current - so it is a hydro-generator. Already 20-30 cm beneath the water surface, there usually is a current.

So on seeing this video, a friend suggested that having this device on board of a yacht could create energy for onboard living.

Given the difference in density of water and air, a 3 mph ocean current has about as much kinetic energy as a 240 mph wind.

The Waterotor has been verified for maximum energy extraction for a water flow speed range from 1 mph to over 20 mph (size and generator match ‘selection’ per size and flow conditions). Efficiency rating is 24 % energy extraction to over 30% – about the maximum expected efficiency for a Savonius rotor.