Carl, I'm initially inclined to disagree with some of the general assertions in your post -- re designs not competing, multiple engineering solutions (at least concerning paddles), and stagnation lines -- but I agree that I should do more research on Aleut paddles.
I must begin, however, with my more than 60 years of observing paddles. The only ones I have ever seen with an aggressive ridge down the center, other than some of these Aleut paddles, are what I would call Walmart paddles. Cheap things, where the builder merely glued flat blades onto a central pole to produce a $25 paddle.
Preliminary reading of forums indicates much confusion as to the power face of an Aleut, but the consensus seems to be that the ridged face is the primary power face, mainly on the authority of someone named Wolfgang Brinck. Some users report greater stability with the ridged face as the power face; others report less power. At least one poster reports flutter when slicing the Aleut.
Do you think the stagnation line concept -- assuming it is relevant to paddles at all -- relates more to paddle flutter or paddle power? I think the concept of a stagnation point, or small stagnation area, may be a more relevant concept for the power face of a paddle than a stagnation line. For example, a concave and curved power face would increase and hold the stagnation area more so than a convex power face. This increases power.
It seems conceivable that a sharp and abrupt power face ridge might result in a less laminar and "bumpier" water spillage off the face than a smoother and more flowing dihedral convexity. After all, a paddle is rarely pulled perfectly flush to the water, and hence that edge seems as likely to cause drag and disturbance as it does smoothly parted waters.
Finally, I can't help but observe that I have paddled with hundreds of canoe and kayak paddles that have no excessive flutter and that none of these has an Aleut ridge. Moreover, no racer in any paddling discipline that I'm aware of uses a paddle with an Aleut ridge. If such a ridge solved any efficiency issue -- flutter, power, slippage -- why haven't racers rediscovered that solution?
These are questions I'm asking mainly to myself as I conduct some further research. I'm not confident, however, of finding anything truly objective and empirical. Hardly anyone spends any real money doing real research on canoe or kayak physics. I think you told me that.
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