Subject: [baidarka] Paddle Dynamics 101
From: Joe Street (jstreet@venus.uwaterloo.ca)
Date: Wed Jun 20 2001 - 10:18:44 EDT
This question of paddle efficiency doesn't seem to die. Aside from
the fact that there was definitely a mathematical error in Peter's post
I think that there is a bigger picture that people are not seeing. This
is what I was getting at in my own post some time back.
There seems to be a lot of talk about hydrodynamics and aspect ratio
in the discussion of efficiency. While it is true that a high aspect
ratio lifting foil is more efficient (i.e. that it produces more lift
for less drag) than a low aspect foil, this doesn't have much bearing on
a paddle. Some people are sure to disagree with me but as I see it a
paddle is a drag producing device not a lift (or thrust) producing
device. Lift is thought of as a vector summation of forces which act
normal (or almost normal) to the flow whereas drag is parallel to the
flow. In paddling the flow is at a very high angle (of attack) to the
blade which means that the blade is in a stall condition which again
indicates that the force felt on the shaft is mainly due to drag.
Even if the paddle enters the water on an angle before being drawn
back so that the flow has some chance of remaining attached to the
forward face the blade would then produce a lift vector which is also
angled ( a smaller portion of it being useful for propelling the kayak)
and it would tend to create a lateral force which would want to capsize
the kayak.
So the question of aspect ratio doesn't really apply when you are
talking about efficiency of DRAG producing devices, at least not in the
same sense as it normally applies to lift production.
Everyone seems to be in agreement that the native style paddles
allow one to paddle further with less effort which in the final analysis
means they are more efficient period. How this comes about is
complicated but it must be looked at from a wholistic viewpoint which
includes the paddler as part of a system which ultimately converts food
and oxygen into forward motion. Paddling at a higher cadence with a
blade that is mathematically less efficient may actually be more
efficient overall due to some other optimization of the metabolic and
circulatory systems in the body.
The point is I guess that we could argue the point forever and in so
doing miss the chance to go out and paddle. So like the other post said
grab a paddle that looks good on you and pose for a picture and then get
the hell out there and paddle with it!!
Flame suit on!
Joe
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