Tim,

While I tend to be more of an "experimenter" in my engineering, I agree that starting from a known point is a good thing. A quick experiment in a bathtub should be easy enough to give you some idea of how the blade works in the water. Video tape it so you can watch the water in slow motion, add some coloring agent to really make the motion more obvious...

I'd try that with a couple different commercial blades, were I inclined to do such an experiment. That way you can see how each works, and then paddle them "in the wild" for a little bit to see which you like as a basis for your own design.

FrankP