David Carlson wrote: > If the boats have the same drag and are going the same speed, then the power > output from the paddles is the same. Absolutely. > If the stroke lengths of each paddler are > the same, then obviously the paddle/paddling technique with the higher cadence > is only half as efficient as the slower cadence. Why? Because force generated > in the direction of boat motion must be the same for each paddler, and power is > force times velocity, and the paddle with the higher cadence must moving with > twice the velocity. That's wrong. You're taking paddling speed as the absolute measure of power input- but that's only part of the equation. The other half is effort. Without it, we have no idea what the energy exerted by the paddlers is. Say we have 2 kayaks moving through the water with a kinetic energy of 50 watts measured on our kayak-o-meter. We have paddler A doing 50 strokes/minute and paddler B doing 100. Is A twice as efficient as B? Answer: We can't say. We don't know how much effort either paddler is putting out. To complete the equation, we need to know that paddler A is working against a resistance of (say) 5 lbs and B against a resistance of 3 lbs, or whatever it turns out to be. Then we can compute the work done by each paddler, and compare it to the energy of the kayak. > Thus, the power input to the faster paddle is more than > that to the slower paddle. Incorrect, for reasons above. > If you're paddling boats with the same resistance the same speed, then the > force on the paddles must be the same ( ignoring rest time between strokes). This assumes that force input to a paddle equates with thrust, which has the implicit assumption that paddle design is irrelevant, and that all paddles and paddlers are exactly as efficient as each other. This is a very large assumption, and not one I think can be justified. > So the conclusion that the larger paddle requires significantly more more > driving force is incorrect. Except that was never claimed. What I said was this: > > If I'm using a Greenland paddle at 120 strokes and you're using a wider > > paddle at 60 and we're keeping pace, and all other factors are equal, > > then I'm probably more efficient. > In that posts, and the preceding ones, I stressed that I was talking about the paddler, and not the paddle. I never claimed that skinny paddles are more efficient than wider ones; they may well be less efficient, for all I know. This seems to have escaped a number of posters who keep claiming I'm wrong when I say narrow paddles are more efficient! Quoting myself once more: > Generally, with humans, as you increase power > > output you get diminishing returns in terms of effort per energy output. > And that was my central point. -- mike ------------------------- Michael Edelman mje_at_spamcop.net http://www.foldingkayaks.org http://www.findascope.com *************************************************************************** PaddleWise Paddling Mailing List - Any opinions or suggestions expressed here are solely those of the writer(s). You must assume the entire responsibility for reliance upon them. All postings copyright the author. Submissions: PaddleWise_at_PaddleWise.net Subscriptions: PaddleWise-request_at_PaddleWise.net Website: http://www.paddlewise.net/ ***************************************************************************Received on Wed May 16 2001 - 19:28:37 PDT
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