Craig Jungers wrote: > Even so a kayak is very easy to propel at very slow speeds. I would > imagine 10 watts would get a kayak to 1mph with no trouble (in no > wind). I'd bet Matt Broze has some data on this somewhere. Intriguing! In fact interesting enough to go to my kayak upstairs and do some measurements: - If I sit down and stretch out my paddle, to where I would usually put it in the water, it's 1.20 meters front of my backrest. Supposing I end my "power" phase where it should, at my hips, I move the paddle through the water for 1.20 meters, from my own perspective. - If I put my paddle in various positions, with the blade against a scale, I hardly can push it above 5 kilograms. I'd guess my average force on the paddle is about 3, during normal touring. - A stroke on one side takes about 1 second. (A full cycle, left and right, will take twice that long. Whenever I talk about a stroke, I mean one slash on just one side.) From there, it's the most basic physics in the world: Force * distance = energy. energy/time = wattage. These are actual _definitions_: Energy is measured in Nm, which means Newtons per Meter. Wattage is defined as Nm per second. Anyway: - Distance: 1.20 meters - Force: 30 Newton (amounts to 3 kg) - Time: 1 second =================== - Output: 1.2*30*1 = 36 Watt. Let's say between 30 and 50. In a full sprint, I could perhaps raise the force to 60 Newton and do it in half a second, creating a burst of 144 watts (let's say between 100 and 200) - for about 10 strokes, perhaps. --------------- Now for the efficiency. I rechecked the 'net for drag tables: http://www.cyberiad.net/library/kayaks/skmag/skmag.htm http://www.keelhauler.org/khcc/seakayak.htm http://www.oneoceankayaks.com/kayakpro/kayakgrid.htm ...and found that they quite consistently measure 1.9 to 2.1 lbf to get a seakayak to a speed of 3 kts, which is my touring speed. That's about 1kg or 10Newton. The distance over 1 second (calculated from the 3-knot speed) is 1.5. Again: Wattage = distance*force/time = 15 watts. FIFTEEN WATTS! What's happening to my other 15!? Well: I have a much slower boat than listed in any of these tables. Efficiency might be as low as 50%, or as high as 99%. Let's hope Matt has more accurate data on paddle efficiency. Time to walk to dog. No one can say that "I should get out more". Niels *************************************************************************** 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 Thu Apr 28 2011 - 16:42:53 PDT
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