Steve Cramer wrote:
....stuff deleted

I was not commenting on whether asymmetry will, as you say, reduce
turbulance, vibration, and cavitation. What I was saying was that you
don't need a lot of blade to propel a boat and that placing the wider
edge into the water will tend to result in excess work and stress for
the paddler (the blade, be it small or large, will only move a few
fractions of an inch when pulled against). Since we were discussing
the injury here, I was pointing out that the load of an inverted
paddle may result in undue stress on the paddler.


I said nothing about "turbulance, vibration, and cavitation", just
torque (i.e., twist). BTW, paddles don't cavitate, they ventilate,
(http://www.guillemot-kayaks.com/Design/Paddlework.html), but that's not
the point here. Yes, you don't need a wide blade to propel a boat. The
Greenlanders proved that over 2000 years ago. But I still don't follow
your point. Would you say it isn't good to totally immerse the blade? Or
that everyone should use narrow blades?

What is written on the site in reference to cavitation vs. ventilation
is as follows:
"Neither is any good, but what your average kayaker creates is ventilation."

My paddle cavitates when I pull hard. It goes in clean, takes no air
down with it, and it generates air bubbles on the low pressure side of
the blade, which is, by definition, cavitation (cavitation is not
limited to propeller blades, but occurs much more frequently due to the
intense pressures the blade places on the water). If I pull really hard,
the vortices on the blade will suck air down toward the paddle, creating
ventilation. This is tremendously inefficient and causes "slippage," as
referred to on the website you cited.

But that, again, isn't the point. Torque isn't the issue here. Paddles
do not generally twist in use. While there may be unbalanced pressure on
various points of the blade, the shaft should not torque on a
well-designed blade, regardless of symmetry.

What I am discussing has little to do with the symmetry of the paddle,
but upon the stresses which cause injury to paddlers. Too much blade
can, and does, cause injury. Using an asymmetric blade upside down puts
the more blade into the water, thus putting more pressure on the
paddler. Whether or not this causes injury is a function of how tightly
the paddler holds the blade and how much stress the lever (paddle)
directs to the joints where tendons meet bone.


Perhaps you've never heard the arguments in favor of asymm paddles. Have
a look here for a nice explanation:
http://www.getoutcanoeing.co.uk/acat...ategory&page=1



I use an asymmetrical paddle and know why. We are discussing two
different things here. More blade = more stress on paddler. Longer shaft
also translates to more stress on paddler, but there are points of
diminishing returns on that. A shorter shaft with a higher cadence
produces fewer injuries than a long shaft. If the shaft is too short,
however, a great amount of efficiency is lost.

A large blade combined with a long shaft can cause injury more quickly
than a narrow blade (though my understanding is that the shaft length is
the bigger issue).

Rick