How to measure force due to a tidal wave?

[Thundagere]

I was thinking about (for experience, since somebody's probably already done it) making a sort of generator, with the shaft of the turbine connected to four perpendicular flat pieces. In water, waves would smash against the pieces, rotating the shaft and hopefully generating electricity.
The main issue is that to get maximum energy, the waves should strike the pieces at an angle of 90 degrees—thus, I need to keep track of how far the pieces rotate. I also need to calculate the time it takes for this, because the waves will have a period and these need to coincide.
Thus, how much force would a tidal wave exert? How would you find this value? I would need to change the resistance on the shaft depending on this and the torque it exerted, so...all ideas welcome!

 

[rock.freak667]

You can check the Wikipedia page on Wave Power. It has an equation that can give you the power of a wave with certain parameters such as period. That will give you a value for P. From other rotational equations such as P=Tω, you can get torque and angular displacement.