The U2 was also a slow plane. And wasn't even faintly nimble. That's why fast planes or nimble planes have much shorter wings. A kayak, even a sea kayak, is very nimble.

If it was so simple for rudders, you wouldn't see the rudder designs on many of the sail boats you do see, which is not a long blade drafting deeply into the water, but is squatter, nnot extending below the keel. Just as airplanes do not have long thin rudders or elevators, but have more paddle like shapes. A significant effect off hand that I can see for boat rudders is the need for drastic action on the part of the helmsman, which a tall thin rudder would not take well. A large wide blade produces much more side thrust to turn the boat with minimal angle change then a long foil, especially at the rather slow speeds a sailboat works in.

A kayak rudder is more to handle boat cocking, not ruddering the boat around like a sailboat. If you were to try to sail a kayak as a sailboat with those tiny rudders, you would be deeply disapointed. At least that's is what I've read and heard on every occassion from those who do sail kayaks and canoes.

Nor would a rudder that is wide fore and aft through the water be hard to turn. As long as it's forces are balanced along the axis of rotation, it would be just as neutral as could be.

Myself, I tend to suspect kayak rudders are shaped the way they typically are because (1) they aren't really rudders in the steering sense, and (2) a small flat blade flips up onto the back of the deck easily and more esthetically then a sailing rudder would.

> It's known as aspect ratio. A long tal rudder is more efficient.
> This is the same reason sailplanes have long narrow wings. If you've
> ever seen the U2 spyplane, it uses the same principle. This is why
> racing sailboats have tall rigs with a short base rather than the
> squatty looking sail rigs that you see on low performance sailcraft.
>

> Also, it makes it easier to turn the rudder. If the hinge line
> is at the rudder's leading edge, the shorter the rudder is (fore and
> aft) the less torque required to turn it.