Niels wrote: >You KEEP dividing those 30 watts by two. I maintain that >you're wrong in all those cases: G'day, Regarding using one or two arms in the calculation of potential energy created by lifting a paddle and the associated power (PE). To the extent that a paddler is lowering both arms simultaneously during the power phase of a stroke then I can see that its justified. However, when carrying through the power stroke my upper hand is held level in the horizontal plane, and passes across my eyes, so I should only use one arm in the calculation of PE for my stroke. Regarding using another factor of two as a crude approximation to account for the times in a paddle stroke when there is no lifting of either blade. The justification is that: 1. during the power stroke I rotate my torso to engage my abs and also to extend the blade's path through the water so that in the later phase of the stroke the blade is neither falling nor rising. 2. few paddle strokes are truly carried out in the vertical plane. Consequently the blade seldom travels quite parallel to the side of the boat but tends to sweep out as it travels backwards and this also has the effect of maintaining the blade at a constant level below the surface of the water during the later phase of the stroke So with the upper hand at a constant level throughout the power phase and with the blade at a more or less constant level below the water during the later phase of the power power phase there is a significant period in my stroke when my arms are static with respect to my torso and I am neither releasing nor creating potential energy due to change in blade height. Thats why I need to use some compensating averaging factor to evaluate the continuous power generated or used. All the best, Peter *************************************************************************** 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/ ***************************************************************************
Hi Peter. Up for another night of rock hard reality? I myself could use a night of solid fantasy - but that can wait. rebyl_kayak_at_energysustained.com wrote: > Regarding using one or two arms in the calculation of potential energy > created by lifting a paddle and the associated power (PE). To the extent > that a paddler is lowering both arms simultaneously during the power > phase of a stroke then I can see that its justified. However, when > carrying through the power stroke my upper hand is held level in the > horizontal plane, and passes across my eyes, so I should only use one > arm in the calculation of PE for my stroke. You certainly need to calculate from the movement of both arms. To make things easy, I used the _average_ movement of my arms in all calculations. I don't have to calculate that average: The middle of my paddle _is_ that average. If one hand drops 60 centimeters and the other 0, the average is 30 centimeters - which is what the center of the paddle does. Now, assuming one hand + half a paddle weights 3kg/30N, you can calculate the potential energy in two ways: - left weight * distance + right weight * distance = 30*0.6 + 30*0 = 18 - total weight * average distance = 60*0.3 = 18 (I consider these numbers unrealistic: All paddlers I've seen drop both hands. It's just for the ease of calculation that I drop only one hand in my example) That's how I calculate my own potential energy: - Total weight = 7kg/70N; - Average drop (middle of paddle) = 0.4 meters; Energy output = 7*0.4 = 28W If I may paraphrase your other argument: You drop the paddle for perhaps 0.2 (or 0.5, or 0.1) seconds out of a total stroke, and you think that changes the calculation. I'll do the math for 0.2 seconds out of each second, to show that it doesn't matter. During the 0.2 seconds of the drop, you release 18Nm of energy (which is the result from my earlier, unrealistic example). You do that in 0.2 seconds, so the energy output during that time is 18/0.2 (wattage = energy/time) = 90W. During the remaining 0.8 seconds, you release no energy to all - so the average energy release over time is 90/5 = 18Nm/s, or 18 Watts. I tend to skip all those calculations, and simply ask "How much energy is released every second?" since that gives the same answer immediately. That's 28 Watts for me - but I've lost track of the estimates of your own numbers. Were you talking the weight of one arm, both arms? Using distance travelled by lower hand or by the center of the paddle? What's your stroke-rate? I'll be happy to repeat the calculations with new data. *************************************************************************** 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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