Mind if I make an attempt at a more rigorous definition of some potentially confusing terms? ... oh goody.... Lets talk about efficiency for a moment. 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... Note the difference between the two kinds of paddles is not that great at six percent. However for racers, six percent is tremendous. For the average paddler, six percent is probably less important, although I will not call it insignificant. The efficiency contrast of the two paddles may be even smaller at recreational speeds. I have no idea where a greenland paddle would fall into an efficiency measurement, although I think another part of the benefit of greenland paddles for touring is that it facilitates the use of many different muscles all in the same day. I wonder if modern science can quantify that benefit. Ok, now lets talk about lift... but first lets talk about drag. The paddler is pulling backwards on the paddle (force vector points towards the stern). The resistance of the water (drag) on the paddle resists that pull (force vector points towards the bow). The drag force vector is slightly smaller than the paddler force vector, which is another way to think about efficiency. The difference in the size of the vectors represents the energy that is lost due to turbulence and the slippage of the paddle through the water. When lift is generated due to laminar flow, the size of the resistance vector is slightly increased because the lift vector points in the same direction as the drag vector. Even if further calculations were to show that the lift generated by Greenland paddles really is insignificant, efficiency is probably still increased because there is a lot less turbulence created by the laminar flow. And note, modern, non-wing paddles can significantly reduce turbulence by slicing the paddle outwards away from the kayak, just like racers and greenland paddlers. Well, the concepts above are quite clear to me, but I wonder how clear it is to the readers. I suppose I could put it down on a web page, with force vector diagrams, and with maybe even a bonus picture of me waving my hands. Anyhow, I hope my definitions make sense, and maybe clear up a little confusion. Cheers, Kevin ___________________ / Kevin Whilden \ |Dept. of Geosciences \___ |University of Washington \ |kwhilden_at_u.washington.edu| \________________________/ *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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/ ***************************************************************************
-----Original Message----- From: K. Whilden <kwhilden_at_u.washington.edu> To: paddlewise_at_lists.intelenet.net <paddlewise_at_lists.intelenet.net> Date: Monday, July 27, 1998 12:57 AM Subject: [Paddlewise] lift and efficiency >Lets talk about efficiency for a moment. > >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... Missing from this list is energy loss in the paddler's body due to heat generation and poor stroking. I believe that this body loss is far more significant than losses due to the paddle/water interaction. Each body is a machine that has an speed/force combination at which it is most efficient. The only way to find the best combination is time trials, using a stopwatch over a known distance. These trials are not just for racers! Try a long narrow blade paddle and a low stroke and compare to a short fat blade with a vertical stroke. Try comparing the same blade and style at different lengths. You don't have to go all out to do these tests. Use what seems to you consistent effort. The results may be surprising. Your subjective sense of which combination is best is not to be trusted without the stopwatch. Jerry *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
I think it is a bit misleading to think of turbulence as merely an indication of inefficiency. Any motion in the water is the _reaction_ from the _action_ of moving your boat forward and as such is both a sign of power being applied and an indication of inefficiency. Even if your paddle is working completely with laminar flow it is still moving the water. The energy lost to moving water does not discriminate between smooth and chaotic motion. If you move (m) grams of water at a velocity (v) the energy involved in moving it is the same. (Have I said the same thing enough times yet?) The inefficiency is also not indicated by slippage (distance between entry and exit), but how much water is moved, and more importantly, how fast. How that water is moved is not important. It is important what direction the water is initially moved. Note that if you were able to place a paddle so the only motion through the water was parallel to the direction of motion (pure drag), all the force applied to it would be used for propelling the boat. As soon as you start moving the paddle off parallel, you introduce a component of drag perpendicular to your motion. This is wasted effort. This is not to imply that good things can not be obtained from that off-parallel motion, but you are introducing another source of inefficiency to your analysis. BTW once the water has moved beyond the influence of the paddle it can move anywhere it wants without effecting efficiency. Nick At 12:30 AM -0700 7/27/98, K. Whilden wrote: >Ok, now lets talk about lift... but first lets talk about drag. The >paddler is pulling backwards on the paddle (force vector points towards >the stern). The resistance of the water (drag) on the paddle resists that >pull (force vector points towards the bow). The drag force vector is >slightly smaller than the paddler force vector, which is another way to >think about efficiency. The difference in the size of the vectors >represents the energy that is lost due to turbulence and the slippage of >the paddle through the water. When lift is generated due to laminar flow, >the size of the resistance vector is slightly increased because the lift >vector points in the same direction as the drag vector. Even if further >calculations were to show that the lift generated by Greenland paddles >really is insignificant, efficiency is probably still increased because >there is a lot less turbulence created by the laminar flow. And note, >modern, non-wing paddles can significantly reduce turbulence by slicing >the paddle outwards away from the kayak, just like racers and greenland >paddlers. > >Well, the concepts above are quite clear to me, but I wonder how clear it >is to the readers. I suppose I could put it down on a web page, with force >vector diagrams, and with maybe even a bonus picture of me waving my >hands. Anyhow, I hope my definitions make sense, and maybe clear up a >little confusion. > >Cheers, >Kevin > ___________________ > > / Kevin Whilden \ > |Dept. of Geosciences \___ > |University of Washington \ > |kwhilden_at_u.washington.edu| > \________________________/ > >*************************************************************************** >PaddleWise Paddling Mailing List >Submissions: paddlewise_at_lists.intelenet.net >Subscriptions: paddlewise-request_at_lists.intelenet.net >Website: http://www.gasp-seakayak.net/paddlewise/ >*************************************************************************** Nick Schade Guillemot Kayaks c/o Newfound Woodworks, 67 Danforth Brook Rd, Bristol, NH 03222 (603) 744-6872 Schade_at_guillemot-kayaks.com http://www.guillemot-kayaks.com/ >>>>"It's not just Art, It's a Craft!"<<<< *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
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