I'm working on an idea that has to do with placing wind turbines on lake beds to catch the constant undercurrents (not a wholy original idea, I know). One of the most important factors to take into consideration is the lateral force exerted on the tower by the current--which is identical to the force exerted by the wind on a wind turbine tower. The only problem is that there is a lot of information that can be found on the coefficient of drag of a spinning rotor in a gaseous fluid (air), whereas I really haven't been able to come across much information regarding the coefficent of drag of a rotor (in motion) submersed in a liquid (such as water). For example, a wind turbine has a coefficent of drag of about .9 while rotating. And the maximum value for an object (such as a parachute) in air is around 1.5. Would these values hold true for the medium of water? Is there some explanation that limits the coefficient of drag to a value of less than 2?