Niels Blaauw wrote: >I made a drawing: >http://www.nibla.nl/tmp/paddlewise/halfway.gif G'day Niels, Very nice drawing and it answers my question well, I can see what you are getting at and it seems to make sense provided one takes out the paddle at the hip or just before reaching the hip. I went on to check how much average power the returned potential energy might save for me. I don't have your original calculation so if you have time perhaps you could check that I'm using similar assumptioms. Arm mass 4kg (roughly 6% of my body weight) Paddle mass 800g Paddle height displacement 35cm Fraction of paddle stroke time that potential energy is being dissipated 0.5 Average crusing power 100W This gives me a power contribution of 17 watts while the paddle is falling through the water and an average power contribution of 8 watts being 8% of my paddling power. I'd suggest that even in a relaxed arm there will still be work done as muscle fibers retain some tension in balancing the arm and paddle weight, also as Matt says the energy to forward conversion efficiency would be an issue too. So as a guesstimate if a third of the energy was converted then 2% to 3% of ones paddling power might come from the potential energy. I'm not sure that this would be true for a an arm moving in a typical 'vertical' or 45 degree paddling stroke. The tension in an arm as it controls paddle position and balance might counter the downward movement of gravity. This would also dissipate energy as the muscle fibres are repetitively triggered faster than their relaxation time to maintain tension. Is it possible to paddle efficiently with relaxed arms during the downward phase of the stroke? If I've understood, then that is one of the points you are making and the principal benefit could be as much in minimising energy dissipated in a tensioned arm as in the potential energy contribution. All the best, PeterO *************************************************************************** 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/ ***************************************************************************
rebyl_kayak_at_energysustained.com wrote: > 1. Arm mass 4kg (roughly 6% of my body weight) > 2. Paddle mass 800g > 3. Paddle height displacement 35cm > 4. Fraction of paddle stroke time that potential energy is being dissipated > 0.5 > 5. Average crusing power 100W (numbered for convenience) Hmmm... 1: Is that the weight of BOTH your arms? 2: Nice paddle! Mine is 1300. 3: Is that at one hand, or in the middle? 4: What's the need for that? It only matters how many times you store and release that potential energy, not how long it takes to release it. 5: That sounds VERY high. Wasn't that what a trained biker could deliver for one hour? I'd say 50 is more likely. Assuming that both your arms and paddle together weight 8.800 grams, you measured the height at the center of the paddle, and you make about 1 stroke per second, you'd get about 31 watts. > This gives me a power contribution of 17 watts while the paddle is > falling through the water and an average power contribution of 8 watts > being 8% of my paddling power. With my more optimistic numbers 50%. > I'd suggest that even in a relaxed arm there will still be work done as > muscle fibers retain some tension in balancing the arm and paddle > weight, also as Matt says the energy to forward conversion efficiency > would be an issue too. So as a guesstimate if a third of the energy was > converted then 2% to 3% of ones paddling power might come from the > potential energy. A conversion of potential energy into kinetic energy (as is done is the forward-resting-stroke) is 100% efficient. It's as efficient as a pendulum, and see how long it can keep going, converting kinetic energy into potential energy and vise versa. Yes: There will be losses in muscle tension - but those doesn't change the energy _output_. It only changes the _input_ of the system. It will dissipate as heat. If 30 watts come out of dropping your paddle, then 30 watts will be transferred to the water, some way or another. There is no where else to go, apart from some joint friction and air resistance. > I'm not sure that this would be true for a an arm moving in a typical > 'vertical' or 45 degree paddling stroke. The tension in an arm as it > controls paddle position and balance might counter the downward movement > of gravity. There will be some tension in your upper elbow, keeping it straight - but that won't interfere with upward or downward motion from the shoulder. There will be some tension in the upper shoulder:You have to keep drawing that arm over your chest, to keep the paddle from falling over your lap. These muscles shouldn't interfere with moving the paddle up or down - or not much. The lower arm has no tension at all, except in the fingers. That arm could be replaced by a rope. It just hangs from the paddle. > This would also dissipate energy as the muscle fibres are > repetitively triggered faster than their relaxation time to maintain > tension. We'd need number on that: Oxygen use at rest, during exercise and at static tension. Does anyone have those numbers? I'd be interesting to include that in this discussion. > Is it possible to paddle efficiently with relaxed arms during > the downward phase of the stroke? If I've understood, then that is one > of the points you are making Yep! Mostly relaxed _shoulders_ though, and at least one completely limp arm. > and the principal benefit could be as much > in minimising energy dissipated in a tensioned arm as in the potential > energy contribution. That's actually why I designed my paddle-carrier: Simply to relieve muscles that (as I thought) add nothing to forward motion. Only much later did it occur to me that there might be more to it. 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/ ***************************************************************************
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/ ***************************************************************************
Niels wrote. >All paddlers I've seen drop both hands. And >If I believe tests and wide-eyed teachers, I have a knack for >finding the easy ways - which is why I (without even thinking) throw out >the timing of your stroke and immediately jump to the wattage. G'day again, Dropping both hands! Come to Sydney Harbour and I'll buy you a beer and then we can go and look at some of our surf ski racers! You can spot them a kilometre away as they have the most stylish stroke in which the hand doesn't drop during the power phase of the stroke. Whether its efficient or ergonomic who knows, but it looks great. Likewise our instructors shout at me if I drop my hand during the power phase, when they ask me to demo the stroke to newcomers. The other times I'm really careful is if I'm sprinting or if I'm dog tired on a long trip. But no one's perfect and I'm quite sure that when I'm slack I drop my hand. For the sake of evaluating the effect of your ideas in my stroke I thought it best to stick with the best stroke that works for me. Impulse Power! Have I spent too much of my life watching Star Trek or helping to design defibrillators and pacemakers:~) I understand what you mean but would also say that the two approaches each have their own virtues. Jumping straight to the average is simple and direct. Breaking down the different phases of power expenditure contributes to a more detailed understanding. They should both give the same result. I came back to work today and was immediately swamped in tenders, reviews and giving evening lectures so won't be able to collate the key data from my posts or look up those other values you wanted in Cycling Science until the weekend. Talk about Hard Reality it's like stepping into a different world getting on to the water - but which world is more real! I promise to do it next weekend though. All the best, PeterO *************************************************************************** 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/ ***************************************************************************
PeterO wrote: > Dropping both hands! Come to Sydney Harbour and I'll buy you a beer and then > we can go and look at some of our surf ski racers! I'd love to! Your view sounds much better than my local canal with the bathtub-rental. > You can spot them a > kilometre away as they have the most stylish stroke in which the hand > doesn't drop during the power phase of the stroke. Whether its efficient or > ergonomic who knows, but it looks great. I bet they do look great - but perhaps we shouldn't get our long-distance-stroke from testosteron-poisened wave-gods. > Likewise our instructors shout at > me if I drop my hand during the power phase, when they ask me to demo the > stroke to newcomers. Do they have any justification for that advice? > The other times I'm really careful is if I'm sprinting > or if I'm dog tired on a long trip. But no one's perfect and I'm quite sure > that when I'm slack I drop my hand. For the sake of evaluating the effect of > your ideas in my stroke I thought it best to stick with the best stroke that > works for me. I started thinking about efficiency when I found out that there's places along the Corsican coast that I can not reach on a one-day-trip. I spent years perfecting my stroke (and designing my paddle-carrier) to be able to visit those places without the risks that accompany multi-day trips: Bad weather getting me stuck for several days on a remote beach without water; running out of beer; getting my lighter wet and having to stop smoking for days; getting arrested for illegal camping. Last year, I _did_ manage to visite those remote places - and was quite disappointed. The most beautiful places turn out to be easy to reach. > Impulse Power! Have I spent too much of my life watching Star Trek If you're talking the Originals and The Next Generation, there's no such thing as "too much Star Trek". Their idea of impulse power is nonsense, though. > I promise to do it next weekend though. Take your time. I value your input, whenever you have time to spare. Take it easy, 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/ ***************************************************************************
PeterO wrote: > I understand what you > mean but would also say that the two approaches each have their own virtues. > Jumping straight to the average is simple and direct. Breaking down the > different phases of power expenditure contributes to a more detailed > understanding. There are right and wrong times to remove data from equations. I just remembered a lecture about some light-therapy that went like this: "If you crush all the mass in the universe together, you end up with something the size of a football. So, there really is _very_ little mass in the universe. All that's left, when you've taken out that little mass, is light - and that's where our light-therapy comes in." Please warn me when I start reasoning like that. I'll have to sober up - a bit. 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/ ***************************************************************************
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