Would anyone know the effect of adding weight to a kayak on the energy required to paddle it. That is, if I double the weight do I double the work I do? Is the effect proportional or something very different? I'm fairly new to kayaking and the web, and brand new to paddlewise. If this is discussed elsewhere, I'll go looking. I did look at John Winter's KAPER formula, since both resistance and displacement are in it. But between my rusty math and ignorance of boat terminology I could not figure the answer to my question. Thanks. Brian Heath *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************
Brian wrote; - >Would anyone know the effect of adding weight to a kayak on the energy >required to paddle it. That is, if I double the weight do I double the >work I do? Is the effect proportional or something very different? There is no simple way to answer this accurately because as you increase displacement various form parameters change too. Wetted surface increase, prismatic coefficient may increase or decrease, length and beam ill increase an so on. But if we assumed the unlikely case that everything remained constant here is an example of what might happen. These are resistance figures for a 13.7' waterline kayak at 215 and 430 pounds. The speeds begin at 2 knots and increase in half knot increments up to six knots For 215 pound kayak 0.760, 1.139, 1.591, 2.252, 3.265, 4.841, 7.435, 10.525 ,13.869 For 430 pound kayak 0.789, 1.184, 1.657, 2.440, 3.784, 5.569, 9.453, 13.703, 18.427 There isn't much difference at low speeds where wavemaking is small but once wavemaking becomes important things happen pretty quickly. At 4.0 knots there is about 15% difference. Keep in mind that, because I haven't included any of the other changes this would be higher in real life. 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/ ***************************************************************************
>There is no simple way to answer this accurately because as you increase >displacement various form parameters change too. Wetted surface increase, >prismatic coefficient may increase or decrease, length and beam ill >increase an so on. But if we assumed the unlikely case that everything >remained constant here is an example of what might happen. These are >resistance figures for a 13.7' waterline kayak at 215 and 430 pounds. The >speeds begin at 2 knots and increase in half knot increments up to six >knots > >For 215 pound kayak > >0.760, 1.139, 1.591, 2.252, 3.265, 4.841, 7.435, 10.525 ,13.869 > >For 430 pound kayak > >0.789, 1.184, 1.657, 2.440, 3.784, 5.569, 9.453, 13.703, 18.427 > >There isn't much difference at low speeds where wavemaking is small but >once wavemaking becomes important things happen pretty quickly. At 4.0 >knots there is about 15% difference. Keep in mind that, because I haven't >included any of the other changes this would be higher in real life. > >Cheers, >John Winters The example you cite is for a very large increase in weight. What if the weight delta were smaller and you made the assumption that the drag difference was zero? Then the inertia would be the only effect. Would it be better to have slightly more weight and be slowed less? Especially in choppy conditions. Another question. If the weight delta were smaller, would the knee of the curve of increased drag occur at a higher speed? If so the effect of increased weight might be less than expected at touring speed. 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/ ***************************************************************************
Jerry wrote; (SNIP of performance prediction of boats of differing displacements ) > >The example you cite is for a very large increase in weight. What if the >weight delta were smaller and you made the assumption that the drag >difference was zero? Then the inertia would be the only effect. Would it be >better to have slightly more weight and be slowed less? Especially in >choppy conditions. > >Another question. If the weight delta were smaller, would the knee of the >curve of increased drag occur at a higher speed? If so the effect of >increased weight might be less than expected at touring speed. The drag will not be zero since for smaller displacement increases the form factors won't change nor will the shape of the drag curve change so long as form factors remain constant although wetted surface will increase. Whether the increase in drag is small enough to be unimportant depends upon the sensitivity of the paddler. If one is concerned about resistance in waves then there are more important factors like the moment of inertia, the vertical prismatic coefficient, the boat length relative to waves (and consequently the period of encounter) and (possibly) the stroke cadence. If there is a benefit to adding weight just for weight's sake it is stability. That is why I invented Genuine Canadian Ballast Rocks (TM). You will note that no where in our advertising do we claim that Genuine Canadian Ballast Rocks (TM) improve performance, make you look younger, improve your sex life, nor will your friends be more attractive and your children better behaved or your laundry come out whiter than ever before. All that will happen is that your boat will be more stable.If you use our Genuine Canadian Radioactive Ballast Rocks (TM) mined from abandoned uranium mines in northern Canada you may become sterile but that is the only known side effect and that may or may not be a good thing. Claims that users of Genuine Canadian Radioactive Ballast Rocks (TM) can detect kidney stones through the sides of skin boats and that they cure prostate cancer are unsubstantiated. 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/ ***************************************************************************
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