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Output power estimations using 2 different methods

Method 1:-
Calculation using simple formula for POWER

Horsepower = Torque (foot pounds) x 2 pi x rpm / 33000 which simplifies to:
Horsepower = Torque x rpm / 5252.

Finding TORQUE by calculating the water pressure on the paddle area using:-
Paddle Area x Length x density of water x (Velcity of current2 / 2 x gravitational constant)
And multiplying this by RADIUS

These results could be reliable but the estimation we have used for the drag coefficient of the paddles is probably underestimated and therefore these results are too low. These figures are derived from the force acting on 1 flat rectangular paddle. In fact the HEB may have 3 V-shaped paddles in the water.


Method 2:-
The following graph is founded on information provided on the internet by Rudy Behrens in his article on designing an undershot waterwheel which can be found on the Backwoods Home Magazine website:-


This method provided information on designing the right dimensional configuration of waterwheel and gives progressively smaller diameters for slower water to the point where it becomes unrealistic applied to very slow rivers.

Spreadsheets (xls) can be downloaded here