It’s a matter of efficiency. The rudder provides us with something we want: a moment of force to turn the kayak. But it costs us something: drag that slows you down. So you want a shape that provides the most turn for your drag and that shape is tall and skinny. The profile of the blade also plays into it’s efficiency for best results you want a rounded front edge and a sharp trailing edge. Another thing to avoid is having any part of the blade forward of the pivot point of the rudder as that will cause the rudder to stall (think loose efficiency) For these reasons coupled with what is easy to mass produce pretty much all commercial rudders are similar. If your going to go through the trouble to make your own rudder working on the profile will probably be the place you could improve most over the commercial rudders (in addition to curing the ugly factor of course)

If I remember correctly, the Wooden Boat press recently published a book about canoe sailing that had a pretty good treatment of rudder design and efficiency for canoe/kayak sized boats. Also any book on boat design would probably address the topic.

: Just had a thought about rudder designs. Rather than have a rudder that is
: vertical why not design one that is horizontal. Catboats don't have a deep
: rudder, rather a large barn door design. Granted most other sailboats do,
: but that is due to the healing angle.

: Additonally, swimming animals (beavers, muskrats, even aligators) use a tail
: that is horizontal vs. vertcal.

: Wouldn't the rudder horizontal serve as less drag and be less of a seaweed
: hook? Would also be less apt to be damaged in a grounding, even with the
: kickup feature.

: I'm sure someone has a thought on this.