Fun fun fun! I've had my morning coffee (allright, tea!), but it's also after lunch, so I'm back to being sleepy. :-)

The thing that first caught my eye and imagination with your design is its similarity to the ailerons of an aircrafts wing. Especially when you just look at the portions below the water line.

Now as I understand it (and Mark K understands it a whole lot better then I), they work by effectively warping the wing without destroying the aerodynamic shape of it, changing the air flow over it, either increasing or decreasing the lift.

Taking that to a symetrical wing, which a kayak is (at least if it's built straight it is), the effect would be the same. I suspect this is very significant. As in when you move your aileron like rudder you warp your kayaks foil, causing lift on the one side of the boat, swinging the end towards it. Which could well feel like a skid, as the whole boat would be engaged in the turn.

This should be markedly different then the effect produced by a rudder, which simply fights the symetrical aerofoil shape of the kayak as a seperate entity. Never working with the total "wing" at all. Which has the boat trying to go straight, the rudder fighting it, creating drag as a result.

As for the overall increased glide, it certainly could be simply a result of better building. But it wouldn't surprise me if you'd stumbled onto a tuned ratio for your boat by accident. The balance between laminar and non-laminar flows is bizzare to me, particularly as it relates to what works best. I've seen designs not work because they were too rough, and others of the same body shape not work because they were too smooth. The tuning of dimples on a golfball is a wonderfull science, as long as you can work with the art of it. You may have lucked out finding just the right tune for your boats rear. Remember, they still haven't figured out why the split nose of some kayak design works as well as it does. Oh lots of theories, but that's all they are. As well all the theories that insist it doesn't help.

Another idea just occured to me also. The slight wiggling capabilities of that rudder could very well be an imitation of the flexibility of a fishes tail, trailing edge in particular. They do get part of their speed and glide by that flexibility. It allows their body to flow with the slight variations of pressure that result from the turbulance of the water over their bodies. Hence the Navy work trying to develop soft skinned subs and such. Since this rudder of yours is part of your hull, and not trailing along behind it, the ability of the rudder to hold flow against the total hull could be substantal as a result. Pure speculation on my part of course.

> Admittedly, subjective, but when engaging the rudder, it feels
> like the stern is actually skidding. Since the rudder doesn't extend
> below the keel like a skeg, I can understand how the lessened drag
> might cause this sensation (and the very tight turning radius) Could
> the angled plane of the rudder from top to bottom be having any significant
> effect? The glide with the new rudder in line (not deployed) still
> seems improved over the flip up Feathercraft rudder when it was locked
> on deck. I don't believe that's possible, but we've been paddling
> the Osprey for several years, mostly without the rudder, and we both
> felt the difference. I tried to talk about boundary layers, coefficients
> of friction, and Dolphin papillae to my wife, but she said, "Not
> in front of the children."

> Tom