Nick writes: - Everything else being equal the paddle with the largest blade area will be the most efficient. - Everything else being equal the lightest paddle will be the most efficient. - Everything else being equal the fastest cadence will be the most efficient. ... but I think I have to take issue with those claims. Nick earlier made a point of distinguishing paddle efficiency from human biomechanical efficiency, but he's confusing the two above. Weight and cadence only come into the equation when you put a human on the end of the paddle. Paddles don't have cadence. Humans do. So yes, the HUMAN with the lighter paddle will be more efficient, simply because he doesn't have to expend energy moving that mass back and forth. Will the human with the higher cadence be more efficient? Not necessarily. If we limit ourselves to the typical range of paddles, the human with the higher cadence will be operating more efficiently, but he or she will only be paddling more efficiently if the paddle is designed to take advantage of that. If I'm doing 60 strokes per minute with a big whitewater paddle and you're doing 120, you're generating a lot more power, but you're no more efficient than I am. You may be less efficient. If I'm using a Greenland paddle at 120 strokes and you're using a wider paddle at 60 and we're keeping pace, and all other factors are equal, then I'm probably more efficient. As for blade area: Not true. A larger paddle will displace a larger volume of water when swept over a given arc, but that's just geometry. Efficiency requires comparing power in to power out. While larger blades can generate more power, that doesn't mean they're more efficient. They also require more driving force, and the payback is not necessarily greater per unit of input. Generally, with humans, as you increase power output you get diminishing returns in terms of effort per energy output. -- mike --------------------------------------------------------------- Michael Edelman mje_at_spamcop.net http://www.foldingkayaks.org (nomadics) http://www.findascope.com (choosing a telescope) *************************************************************************** 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/ ***************************************************************************
David Carlson wrote: > If the boats have the same drag and are going the same speed, then the power > output from the paddles is the same. Absolutely. > If the stroke lengths of each paddler are > the same, then obviously the paddle/paddling technique with the higher cadence > is only half as efficient as the slower cadence. Why? Because force generated > in the direction of boat motion must be the same for each paddler, and power is > force times velocity, and the paddle with the higher cadence must moving with > twice the velocity. That's wrong. You're taking paddling speed as the absolute measure of power input- but that's only part of the equation. The other half is effort. Without it, we have no idea what the energy exerted by the paddlers is. Say we have 2 kayaks moving through the water with a kinetic energy of 50 watts measured on our kayak-o-meter. We have paddler A doing 50 strokes/minute and paddler B doing 100. Is A twice as efficient as B? Answer: We can't say. We don't know how much effort either paddler is putting out. To complete the equation, we need to know that paddler A is working against a resistance of (say) 5 lbs and B against a resistance of 3 lbs, or whatever it turns out to be. Then we can compute the work done by each paddler, and compare it to the energy of the kayak. > Thus, the power input to the faster paddle is more than > that to the slower paddle. Incorrect, for reasons above. > If you're paddling boats with the same resistance the same speed, then the > force on the paddles must be the same ( ignoring rest time between strokes). This assumes that force input to a paddle equates with thrust, which has the implicit assumption that paddle design is irrelevant, and that all paddles and paddlers are exactly as efficient as each other. This is a very large assumption, and not one I think can be justified. > So the conclusion that the larger paddle requires significantly more more > driving force is incorrect. Except that was never claimed. What I said was this: > > If I'm using a Greenland paddle at 120 strokes and you're using a wider > > paddle at 60 and we're keeping pace, and all other factors are equal, > > then I'm probably more efficient. > In that posts, and the preceding ones, I stressed that I was talking about the paddler, and not the paddle. I never claimed that skinny paddles are more efficient than wider ones; they may well be less efficient, for all I know. This seems to have escaped a number of posters who keep claiming I'm wrong when I say narrow paddles are more efficient! Quoting myself once more: > Generally, with humans, as you increase power > > output you get diminishing returns in terms of effort per energy output. > And that was my central point. -- mike ------------------------- Michael Edelman mje_at_spamcop.net http://www.foldingkayaks.org http://www.findascope.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/ ***************************************************************************
>David Carlson wrote: > >> If the boats have the same drag and are going the same speed, then the power > > output from the paddles is the same. Actually no. The power output by the paddle is the shown by how fast you move the boat, plus how fast you move the water. You are moving both, so your power output must account for both. If all you had to look at was how fast you moved the boat then everything would be 100% efficient. -- Nick Schade Guillemot Kayaks 824 Thompson St Glastonbury, CT 06033 (860) 659-8847 *************************************************************************** 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/ ***************************************************************************
Michael Edelman wrote: > David Carlson wrote: > >> If the boats have the same drag and are going the same speed, then >> the power >> output from the paddles is the same. > > Absolutely. > >> If the stroke lengths of each paddler are >> the same, then obviously the paddle/paddling technique with the >> higher cadence >> is only half as efficient as the slower cadence. Why? Because >> force generated >> in the direction of boat motion must be the same for each paddler, >> and power is >> force times velocity, and the paddle with the higher cadence must >> moving with >> twice the velocity. > > That's wrong. You're taking paddling speed as the absolute measure of > power input- but that's only part of the equation. The other half is > effort. Without it, we have no idea what the energy exerted by the > paddlers is. My discussion was considering only how much work is being done by the paddle vs. how much work goes to propelling the boat. The paddle puts out exactly as much power as was put into it. There is no significant friction or other energy dissipating mechanism internal to the paddle. So the difference between effort (paddler output) and paddle output is nil. The only effort I am neglecting to consider is physiological, and internal to the paddler. > > > Say we have 2 kayaks moving through the water with a kinetic energy of > 50 watts measured on our kayak-o-meter. We have paddler A doing 50 > strokes/minute and paddler B doing 100. Is A twice as efficient as B? > > Answer: We can't say. We don't know how much effort either paddler is > putting out. > > To complete the equation, we need to know that paddler A is working > against a resistance of (say) 5 lbs and B against a resistance of 3 > lbs, or whatever it turns out to be. Then we can compute the work done > by each paddler, and compare it to the energy of the kayak. Remember that we said that the boats had the same resistance and same speed. Hence the resistance force on the boats are the same and the power is the same (your 50 watts). I said that under these conditions and if the stroke length was the same, then the paddle doing 50 strokes/minute is more efficient. If the stroke length of the paddle doing 100 strokes/min is half that of the paddle doing 50 strokes/min, then the efficiencies are the same. The effort the paddler is putting out is strokes/minute times feet/stroke times force on the paddle. > > > >> Thus, the power input to the faster paddle is more than >> that to the slower paddle. > > Incorrect, for reasons above. No, please read what I wrote very carefully. > > >> If you're paddling boats with the same resistance the same speed, >> then the >> force on the paddles must be the same ( ignoring rest time between >> strokes). > > This assumes that force input to a paddle equates with thrust, which > has the implicit assumption that paddle design is irrelevant, and that > all paddles and paddlers are exactly as efficient as each other. This > is a very large assumption, and not one I think can be justified. There is no assumption here. The only forces on the boat are resistance and, by means of the paddler, the force of the water on the paddle. For a boat traveling at constant speed the component of the force of the water on the paddle that is parallel to the direction of travel of the boat must be exactly equal to the force of resistance on the boat. You can draw a free body diagram of the boat/paddler/paddle system to visualize this. This does not imply that paddle design is irrelevant. Some paddles will take more velocity to generate the required force. Power=Force*Paddle Velocity=Force*strokes/min.*feet/stroke. The constant is Force in the direction of boat travel. > > >> So the conclusion that the larger paddle requires significantly more >> more >> driving force is incorrect. > > Except that was never claimed. > > What I said was this: > >> > If I'm using a Greenland paddle at 120 strokes and you're using a wider >> > paddle at 60 and we're keeping pace, and all other factors are equal, >> > then I'm probably more efficient. >> I quote from your post: "While larger blades can generate more power, that doesn't mean they're more efficient. They also require more driving force, and the payback is not necessarily greater per unit of input. " > In that posts, and the preceding ones, I stressed that I was talking > about the paddler, and not the paddle. I never claimed that skinny > paddles are more efficient than wider ones; they may well be less > efficient, for all I know. This seems to have escaped a number of > posters who keep claiming I'm wrong when I say narrow paddles are more > efficient! Read from your last sentence: "... when I say narrow paddles are more efficient!" Are you talking about the paddler or the paddle? It is entirely possible that for some people, paddling at a higher cadence is easier. If that is the thrust of what you and many others are saying, then I agree. I only meant to point out that in our case of the 50 stroke/minute vs 100 stroke/minute paddles that, if the stroke lengths are the same and the boats are going the same speed and have the same resistance, the paddler doing 100 strokes/min. has a lot of inefficiency to make up for. > > > Quoting myself once more: > >> Generally, with humans, as you increase power >> > output you get diminishing returns in terms of effort per energy output. >> > And that was my central point. OK. Just remember that in the example of my previous paragraph, the paddler going 100 strokes/min is putting out twice the power as the one doing 50 strokes/min. Per your quote, that means that the paddler going 100 strokes/min must be putting out more than twice the effort of the paddler with the slower cadence. Obviously, the example of my previous paragraph is implausible. The only explanation for the faster paddlers efficiency is that his strokes are less than half as long! Regards, Dave Carlson > > *************************************************************************** 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/ ***************************************************************************
David Carlson wrote: > ... > My discussion was considering only how much work is being done by the > paddle vs. how much work goes to propelling the boat. The paddle puts > out exactly as much power as was put into it. There is no significant > friction or other energy dissipating mechanism internal to the > paddle. So the difference between effort (paddler output) and paddle > output is nil. The only effort I am neglecting to consider is > physiological, and internal to the paddler. You're making two contradictory claims. One, that power output is equal to power input for all paddles. Two, that some paddles are more efficient than others. Since efficiency is a measure of the ratio between power input and output, you've sort of disproved your claim via a classic reductio argument. If in fact some paddles are indeed more efficient than others- and that is not a claim I have ever made- then you have consider how much useful work is done by the paddle, and how much just goes into heating the water. That's why I stressed boat speed as a measure of useful work done. Since we're not paddling in a calorimeter our only measure of power output is boat speed. So while the energy coming out of the paddle is equal to that going in, minus some negligible hysteresis losses, that's still not the entire story. But we're really still arguing two separate issues. My position was that a human is more efficient at producing lower output over a long period of time than at producing high output for a short time. Biomechanical studies bear that out, and that is why narrow paddles tend to be better for distance paddling. -- mike --------------------------------------------------------------- Michael Edelman mje_at_spamcop.net http://www.foldingkayaks.org (nomadics) http://www.findascope.com (choosing a telescope) *************************************************************************** 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/ ***************************************************************************
At 2:53 PM -0400 5/16/01, Michael Edelman wrote: >Nick writes: > > - Everything else being equal the paddle with the largest blade area >will be the most efficient. > - Everything else being equal the lightest paddle will be the most >efficient. > - Everything else being equal the fastest cadence will be the most >efficient. > >... but I think I have to take issue with those claims. Nick earlier >made a point of distinguishing paddle efficiency from human >biomechanical efficiency, but he's confusing the two above. Weight and >cadence only come into the equation when you put a human on the end of >the paddle. Paddles don't have cadence. Humans do. > >So yes, the HUMAN with the lighter paddle will be more efficient, simply >because he doesn't have to expend energy moving that mass back and >forth. > >Will the human with the higher cadence be more efficient? Not >necessarily. If we limit ourselves to the typical range of paddles, the >human with the higher cadence will be operating more efficiently, but he >or she will only be paddling more efficiently if the paddle is designed >to take advantage of that. If I'm doing 60 strokes per minute with a big >whitewater paddle and you're doing 120, you're generating a lot more >power, but you're no more efficient than I am. You may be less >efficient. > >If I'm using a Greenland paddle at 120 strokes and you're using a wider >paddle at 60 and we're keeping pace, and all other factors are equal, >then I'm probably more efficient. > >As for blade area: Not true. A larger paddle will displace a larger >volume of water when swept over a given arc, but that's just geometry. >Efficiency requires comparing power in to power out. While larger blades >can generate more power, that doesn't mean they're more efficient. They >also require more driving force, and the payback is not necessarily >greater per unit of input. Generally, with humans, as you increase power >output you get diminishing returns in terms of effort per energy output. I did say "all other things being equal". Which, as someone pointed out, is a bit of a cop out, but is the only way to understand what is going on. If you have a higher cadence but use a different size paddle than two things are different and the comparison is more complicated. I believe the higher cadence is both physiologically (within limits) and physically more efficient. Of course that assumes _everything_ else stays the same. And all other things being equal, a larger paddle creates more lift when used as a wing or more drag when used as a parachute, so everything else being equal, it is more efficient. Unfortunately, something else always changes, so it is hard to make a realistic comparison. Since changing one parameter always changes another, it is theoretical possible to optimize all the parameters to get the "best" paddle. And since there are physiological limits to what the human body can perform, the design that is physically/mechanically the most efficient, may not end up being the most efficient when used within those limits. And since everyone has different physiological capabilities, the most efficient paddle design will be different for everyone. I would be very surprised if the a native/greenland/inuit/aleut/traditional style paddle didn't turn out to be the one of the most efficient for some people in some situations. I'm sure that there are probably multiple "best" designs for a given person in given conditions because there are so many parameters that can be changed -- Nick Schade Guillemot Kayaks 824 Thompson St Glastonbury, CT 06033 (860) 659-8847 *************************************************************************** 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/ ***************************************************************************
Once again I have been guilty of not communicating precisely, something my wife accuses me of from time to time... Let me try to clarify: Nick Schade wrote: > >David Carlson wrote: > > > >> If the boats have the same drag and are going the same speed, then the power > > > output from the paddles is the same. > > Actually no. The power output by the paddle is the shown by how fast > you move the boat, plus how fast you move the water. You are moving > both, so your power output must account for both. If all you had to > look at was how fast you moved the boat then everything would be 100% > efficient. I obviously didn't mean that. I think I meant to say that the useful bower output, which is that required to overcome the resistance of the boats through the water, must be the same. Given paddles generating the same force on the paddle blade, the PADDLE with the highest speed is generating more power, and if these paddles are being used to propel the boats mentioned above, the paddle with the fastest speed is wasting more power, and is the less efficient. Michael Edelman wrote: > David Carlson wrote: > > > ... > > My discussion was considering only how much work is being done by the > > paddle vs. how much work goes to propelling the boat. The paddle puts > > out exactly as much power as was put into it. There is no significant > > friction or other energy dissipating mechanism internal to the > > paddle. So the difference between effort (paddler output) and paddle > > output is nil. The only effort I am neglecting to consider is > > physiological, and internal to the paddler. > > You're making two contradictory claims. One, that power output is equal > to power input for all paddles. Two, that some paddles are more > efficient than others. Since efficiency is a measure of the ratio > between power input and output, you've sort of disproved your claim via > a classic reductio argument. Yes, it appears that I have been imprecise. I am claiming that the effort, or power put into the paddle by the paddler is the same as that put into the water by the paddle. Not all of it provides propulsion for the boat. This last point is where paddles and paddlers/paddle technique are different. For the efficiency calculation, power input would be power input by the paddle to the water, or effort put into the paddle by the paddler, which is the same. Power output would be that power which is actually required to overcome the resistance of the boat. > > > If in fact some paddles are indeed more efficient than others- and that > is not a claim I have ever made- then you have consider how much useful > work is done by the paddle, and how much just goes into heating the > water. That's why I stressed boat speed as a measure of useful work > done. Since we're not paddling in a calorimeter our only measure of > power output is boat speed. > > So while the energy coming out of the paddle is equal to that going in, > minus some negligible hysteresis losses, that's still not the entire > story. I think we're in agreement here, if the boats and their loads are the same, except that I claim that both paddles and paddling techniques can have different efficiencies. > > > But we're really still arguing two separate issues. My position was that > a human is more efficient at producing lower output over a long period > of time than at producing high output for a short time. Biomechanical > studies bear that out, and that is why narrow paddles tend to be better > for distance paddling. I agree with your assertions about humans and their power output. I don't think that we have proved that narrow paddles are more efficient at any power output. I have asserted that for a given propulsive power requirement, if the paddle providing it is moving faster, it is less efficient and the power used to drive the paddle must be more. This is because the forces of the water on the paddle in the direction of boat travel must be the same as the boat resistence (i.e., the same for any paddle providing the required propulsive power). If power output from the paddle is force on the paddle times velocity of the paddle and the force on the paddle is determined by the boat characteristics and speed, then the only thing the paddle characteristics determine is the paddle velocity required to generate that force. If more paddle velocity is required, the paddle is less efficient. Note that with some minor changes, this analysis could be made to accomodate the case where significant "lift" is involved, although Nick has addressed this in a previous post. Regards, Dave *************************************************************************** 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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