Peter wrote; > Why are you assuming that the important objective is high thrust per unit > The maximum thrust that can be generated from a given blade size > is not necessarily the most efficient paddle, efficiency has to be > measured > as energy in vs. energy out, or more accurately thrust output vs. work > input. Why not? Why doesn't this connect to paddle effciency sort of like Lift/Drag ratio? > > An aircraft analogy is Short Take-off and Landing airplanes (STOL). The > wings are shaped to generate high lift per unit area, at the expense of a > very draggy wing design in normal cruise (higher speed) mode. The highest > lift per unit area on a wing yields a very slow and inefficient aircraft. > The most efficient aircraft do not have high lift wings, but rather high > L/D > (or lift to drag ratio) wings. Is there no difference between optimizing thrust and optmizing the lift/drag ratio? If not then are you not assuming that lift provides the bulk if not all of the propulsive force? Why would lift/drag ratio be analgous to developing optimum thrust? Is it not true that one seeks to optimize the best trade off between to forces while the other seeks to optimise a single net force? >There is a relatively simple way to do objective testing on paddles, in >real >conditions in a real kayak. (SNIP) >The paddler must maintain exactly the same speed with the different >paddles, >and then he simply records his heart rate, or air consumption. How would this paddler maintain consistent identical strokes? Would it not be possible that he could be using a poorer stroke with one test than with another and while maintaining the same speed use more energy? (SNIP) > It also might be that the same >paddle shape and size is not most efficient for everyone. Given the variability of people that makes tremendous sense. >I would also suspect that the paddle that is most efficient at a given >speed, may not be the one that is most efficient at another speed. Do we have to prove that beyond what has already been done in the tank by Jackson et al. > It would interesting to >build a set of "test" paddles that vary only one feature or aspect between >each; for example, make several paddles with exactly the same shape, but >different size. Or make them exactly the same cross section (foil shape), >and the same area, but with different aspect ratios. Why would the results already obtained in a tank not apply? >This same test could be used to test hull designs as well (using the same >paddle of course). Why would you want to test boats this way when we already have a method that naval architects have found suitable over the past 100 plus years? >The best stroke mechanics for one paddle would not be the best for another, >which might lead to >one to believe a less than optimum blade shape is >better than another if you do not use the >correct stroke mechanics with it. By this do you mean that paddlers cannot learn appropriate stroke mechanics or do you mean that some paddlers lack the ability to learn proper stroke mechanics and may need a special paddle to suit their particular difficulty? >A simple flow test that I have thought of doing to help visualize the flow >over the blade would be to tape short lengths of bright colored yarn or string on various places on the blade and go paddling with it. Why would not a tank test provide greater accuracy than the variable paddler? Cheers John Winters *************************************************************************** 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/ ***************************************************************************
John Winters wrote: > Why would you want to test boats this way when we already have a > method that naval architects have found suitable over the past 100 > plus years? From the Hobie discussion, isn't it possible that some hull forms might be more efficient when powered by a pulse (paddle) than continuous (constant pull in tank) force. so maybe tank tests could be devised to more closely simulate that? GaryJ *************************************************************************** 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/ ***************************************************************************
John Winters wrote: > Why would you want to test boats this way when we already have a > method that naval architects have found suitable over the past 100 > plus years? GaryJ responded: >>>>>From the Hobie discussion, isn't it possible that some hull forms might be more efficient when powered by a pulse (paddle) than continuous (constant pull in tank) force. so maybe tank tests could be devised to more closely simulate that?<<<<<< I'd like to test kayaks with a paddle that can measure the force applied to it and the angle of the paddle at the time the force is applied because the paddle force is off center and thus causes the kayak to yaw some back and forth as it goes through he water (and towing tank tests do not account for this and it would be very difficult to simulate the correct amount for each kayak and each speed). Last February I suggested to Chris Cunningham at Sea Kayaker that he might be able to put me out of a job (drag prediction) with one of these for a paddler. Back then weba-sport was advertising one for paddles but I don't see it now on their website and the old links don't work. I think Chris inquired about them then and they weren't yet ready. Maybe the company didn't get much interest and decided not to develop a paddle version or they are still trying to work out problems and don't have any in production. http://www.weba-sport.com/weba/rowx_outdoor.html Matt Broze www.marinerkayaks.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/ ***************************************************************************
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