: Hi Bill thanks for the input I talked with a friend of mine who is
: really into rc airplanes and is building molds to create a kit.
: He went over the aero aspect of foil shapes with me and I took
: in alot of what he was saying so my understanding has increased.
: He did have one question though if you don't mind, when it came
: to the term "stall" in aerodynamics the wing would
: have be be on such an angle that the one side could not get any
: air over it to stall ( sorry for my lack of grace in explaining
: what he said) and in the application of a skeg he could not see
: how this could be achieved in a kayak and was wondering if there
: was a further explaination to better his understanding.

: Thanks
: dave g

I think stalling in the sense that we are using it in regard to water is not really stalling in the airfoil sense.

What happens when a foil is travelling through surface water at speed is that air gets drawn down the foil and the flow of water detaches from the low pressure side of the foil causing it to loose lateral resistance. From what I remember this is known as cavitation. This happens very easily with a windsurfer which has speed and and a lot of sideways force applied to the fin. A recipe for disaster unless the shape is perfect. For that reason windsurfer fin design and efficiency has evolved radically in the past couple of decades.

Cavitation with a kayak rudder or skeg, even if it happened, which I doubt is possible, would almost certainly self correct as soon as the speed of the boat dropped and the water flow over the surfaces reattached.

Unless someone comes up with a planing kayak powered by sail I would think that rudders or skegs made form sections of dustbin lids would serve almost as well as refined shapes for course correction and weathercocking control.

If foils were really much better they would be found on all production boats because they would be a selling point. We don't depend on the efficiency of foils like windsurfers do, we use refined shapes because they are more beautiful and we like them on an aesthetic level.

Et