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Kayak and Canoe Design Bulletin Board
can't find article but....
Posted By: Randy Knauff In Response To: Rudder Design Parameters? (Paul Jacob)
Date: Monday, 3 May 2004, at 1:31 p.m.
: I've seen lots of rudders and I've begun to wonder if there are any actual
: design parameters that can be used to design a rudder with maximun turning
: power along with minimum drag. I've heard the Sealine rudders have very
: good turning power and are also low drag. They are a high-aspect ratio
: foil shape which may be a clue.: Any actual design principles or resources that anyone knows of?
: Paul
I read a good research article a while back, don't remember if it was on the web or in a magazine and can't find it now. But what it measured was speed of turning four different kayaks with and without using the rudder.
In a good number of trials, all four kayaks turned faster without using the rudder and by using correct edging and paddle strokes.
Unless you are making large arc slower turns, rudders are slower and to put them at an angle for a quicker turn, paddlers usually go past the point of water flowing around them smoothly to the point they cause turbulence and drag. This does turn the kayak but similarly to dragging your paddle or doing a back sweep, it kills off forward momentum.
Rudders on kayaks, like skegs, are really designed for tracking so all of your power can go into forward movement rather than corrective strokes. But they do turn, even if not as efficiently.
All that said, I paddled with a very experienced paddler last Saturday who has a Sealine on his present kayak and wished for a bit bigger blade. I have played around with making various rudders and blades but haven't found any difference in drag for normal paddling that I could feel. The larger blades do catch more wind while up, which is most of the time.
Airfoil (waterfoil?) shape certainly would be more efficient, but you can't even deflect those much before you break the flow and cause turbulence/drag.
I used a skegged kayak last week for the first time and liked it a lot. May put one on one one of my homebuilts instead of a rudder.
Randy
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