Kevin wrote; > >Loosely defined, efficiency means the ratio of power output over power >input. Ealier, John Winters quoted some efficiency numbers, .92 for modern >wind paddles, .86 for regular modern paddles. He didn't state the exact >application of the these numbers, but I would hazard a guess that it means >that for every 100 watts of paddler effort, 92 watts of are translated >directly into forward motion of the boat (86% for regular paddles). The >other 8 watts are lost due to turbulence, slippage of the paddle through >the water, flexing of the paddle shaft, etc (SNIP) The figures are from "The Hydrodynamics of Paddle Propulsion" by P.S Jackson, N. Locke and P.Brown of the University of Auckland Department of Engineering. They presented the paper at the 11th Australasian Fluid Mechanics Conference at the University of Tasmania, Hobart, Australia. Jackson uses vortex theory to explain how the paddles work which may or may not be easier for people to understand than Kevin's explanation. They supported their theory with tank testing. Their device used an air cylinder while mine used a falling weight. Theirs was superior because they could control velocity and pulse. (My excuse is that I did not have research grant :-)) My feeling was that they missed the boat a bit by not testing the conventional LAR (Low Aspect Ratio) paddle using the same stroke mechanics that were used for the wing paddle. Using their method it might be possible to get some insight into the relative efficiencies of recreational paddles and strokes. Cheers, John Winters Redwing Designs Specialists in Human Powered Watercraft http://home.ican.net/~735769/ *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************Received on Mon Jul 27 1998 - 04:53:12 PDT
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