I wrote: > In fact, some of that misdirected > energy is taking the load off your "paddle holding up" muscles. Niels responded: >>>At the front of the stroke: Yes. At the back of the stroke: Exactly opposite. In the seakayer I put online ( http://www.nibla.nl/tmp/paddlewise/ExampleStroke/ ) I see the blade going in at 45 degrees and comes out at 45 degrees. The forces up and down through the whole stroke cancel out.<<<<< Below you seem to contradict this (and correctly I think). Given your pivot at the shoulder model and gravitational paddling theory, any resistance to the blade (and even the falling of the blade before it meets water resistance) throughout the stroke should allow the paddler to relax the paddle holding up muscles except when lifting the hands and paddle out of the water to prepare for the next stroke. >>>>Assuming his hands and paddle on a scale would measure 7 kilos (70N), and he lifts the center of his paddle (which is the center of gravity) 40 centimeters each second, I calculate that each second he expends 0.4*70 (force * distance) = 28Nm of energy. Since he does that every second (which he does), that 28W.<<<<<< You must have very heavy arms or a really heavy paddle. Maybe you agree with Derek H. who (at least years ago) advocated using a heavy paddle because he felt it added "momentum" to his stroke. Personally, I like to use the lightest paddle with the lightest blades I can (given enough strength to have a durable paddle). My paddles weigh about .6 of a kilo total and my arms (out at my hands if relaxed at the shoulder but held straight at the elbow) weighed in at less than 1.5 kilos each (when resting on a scale at shoulder height so the arm is level). So all the potential energy I'm going to get is only going to be the result of half of what you are claiming for arm and paddle weight. Furthermore, I think you may be also exaggerating the force by measuring the middle of the paddle going up and down and using the weight of both arms for each stroke. Since once the blade is in the water and meeting resistance only one arm is lifting about 1/2 a paddle to get into position for the next stroke. Have you thought about measuring how much each hand goes up and down and using the weight of just that arm and 1/2 the paddle weight to calculate the potential energy available for gravitational propulsion? I think the efficiency of paddle propulsion is less than 50% so the higher you lift the paddle the more energy you waste in the transfer to boat propulsion. Since it is easy to do 3 knots with a low, elbows at the side, Eskimo type stroke (driven by a small waist pivot) why keep working against gravity and wasting more than half the energy you put in to lifting the paddle just so you can teach a sprint racing stroke because that's what everyone else around you teaches. Why not risk the ire of the governing bodies, who's main mission is trying to train future racers, by pointing out how wasteful that racing stroke is for those paddlers just wanting to put around at a nearly effortless 3 knots. BTW, you don't need an Eskimo replica paddle to use the Eskimo stroke. I do it all the time with a feathered Euro paddle. Perhaps that is one reason why it doesn't bother me to go very slow, I'm not having to hold up the paddle weight (as little as it is) using my trapezoids and can just rest it on my cockpit between strokes if I want because I don't have to lift it hardly at all to use it again from that position. >>>>>OF COURSE there will be energy loss in turbulence - as in any other stroke. The part I'm talking about is the energy conversion of potential energy into force and movement, BEFORE it is dissipated by the water. All I'm saying is that the 30W of output ends up pushing water, in whatever direction it might be.<<<<<<< Do you agree that the power available to drive the kayak is whats left after much of that potential energy has been disapated? Maybe you should measure the power using how far the paddle falls before it encounters resistance from the water (or how much you had to lift it when it was out of the water and not being supported by the drag due to the paddle blade in the water holding it up). Since my potential energy available doing the same thing will be far less than 30 watts (due to light paddle and arms) and probably far less than that half that will be directed to moving the kayak I don't see of what importance is a high potential energy if most of it will be later wasted and you had to put an equal amount of kinetic energy into the system lifting the arms and paddle to have the potential energy be that high in the first place. >>>>>>>You'd agree that, in a vacuum, there would be no losses? That's all I wanted to say. Then again: In a vacuum my kayak wouldn't slow down when I stopped paddling, so in a vacuum the question is not valid.<<<<<< No, if the spring is metal (and therefore not a perfect spring) there will be heat losses from the movement of the spring's molecules against each other. I will agree that since we live in the real world of friction and energy losses, accelerating against a drag is a large user of energy, much more than from just maintaining a constant speed. Which was my original point before, you began using what I consider an unrealistic example by operating in a vacuum. I wrote: > Those muscles get a rest because some of your paddling energy (where ever it > comes from) is resisting the paddle sinking because of the blade angle at > entry. Niels responded: >>>>>Think of my model. I can keep its arms from falling down by pushing horizontally against the paddleblade. (I'll film it if I have to). There's no need for any upward force from the outside: Your shoulders will take care of it, without the use of any muscles.<<<<< I was wrong and you are correct here, the fall and then the resistance all through the stroke (pivoting freely from the shoulders) is allowing the paddle holding up muscles to relax. This does seem to contradict your earlier statement though, that things are just the opposite when the water is being lifted at the end of the stroke. Even then it is retarding the paddle and the paddle holding up muscles can be relaxed (but before then the energy from gravity will have likely been so completely dissipated that what little residual energy is left is now having to lift water against gravity and will have stopped the (relaxed gravity powered) stroke from getting that far anyway. >>>>> That's assuming that the water will carry a substantial part of the weight of at least your downward blade. What's the volume of a blade? I hardly think the buoyancy could be significant, compared to the 3 to 4 kilo weight of one hand and half a paddle.<<<<<< That depends on the volume of the blade and the weight of your arms and paddle. Niels wrote: >>>>>>> You have to use some muscles in the shoulder of your upper arm, to keep > the paddle from falling over your lap. That force can be directed > strictly sideways. Apart from that, no muscles are needed. While the > arms fall down, the blade moves practically horizontally through the > water, directing the force exactly where we want it. Using muscles to > keep the paddle up in any other way would be counter-productive.<<<<< > I asked: I don't understand what you are trying to say above. Can you give me a better > description and explain why? And where is it we want the force directed and > why there? Niels responded: >>>>>>You seem to think that I'd HAVE to put an upward force on the paddle to keep it in check. I don't: The horizontal force of the water will do fine. Do I need to make a new video, showing how I can keep my model in check?<<<<< I'm more confused than ever. Please provide a detailed description of what you mean here. As best I can see you are using your upper arm to lift half the paddle up against gravity to get the potential energy for the next stroke, but your mechanical model has both arms falling down to power the stroke (and both must be lifted on the model to set up the next stroke--sort of like a high kneel canoe stroke). How do you do this with a sideways directed force? How do your get up...from sideways? I'm really confused and need a much better description of what you mean here. I wrote: > A buoyant blade would bob up and down during the stroke sinking from the > gravitational energy (then holding up the paddle) and propelling it back up > again to get some more of that potential energy that you seem to like to use > back (and for free). Niels responded >>>>>>I think such a bobbing paddle would _hamper_ the use of potential energy. The blade _should_ be allowed to go down freely: Only the horizontal force can be put to good use, so all other forces are best kept minimal.<<<<<< Why do you think that? It seems to me that if the buoyancy bounce were timed right, you could save your muscles from needing to accelerate the paddle as much in lifting it against gravity. Some paddlers (including some of those who like traditional native type wood paddle) like a buoyant blade and feel that this helps them use less energy because of this rebound. Since the kinetic energy is being rapidly disapated anyway as soon as the blade contacts the water most will probably be gone before the blade ever gets to vertical whether it is buoyant or not. A buoyant blade will save you from much of the distance you will have to lift this paddle thereby cutting your loses inherent in the transfer of energy (from lifting the arms and paddle against gravity into the forward motion of the kayak). I wrote: > During paddling the blade hardly moves at all once it is planted in the water. > It has so much drag that the kayak is pulled past it while it moves very > little in the opposite direction. Niels responded: Back to my example-paddler at http://www.nibla.nl/tmp/paddlewise/ExampleStroke/ : In the video, there's little reference on the water or in the background to see how far the paddle moves. Judging just from the splashes, I'd say that his hands remain almost stationary above the water, but the blade underneath moves quite a bit (Close to a METER at the tip). You are wrong here. The stationary pivot point of a paddle during a stroke is near the water's surface (and with especially long blades may even be below the surface--wasting some energy pushing the upper part of the blade the wrong way--forward in the water, partly retarding the other part of the paddles propulsion). Try paddling near some lily pads or other fixed objects in the water and watch where the paddle goes into the water and where it comes out of the water. I'll bet you will see it is at the same place. You could also look at a video of a paddler moving across the TV screen and using stop action and a small sticker find the point on the paddle shaft that is stationary during a stroke. Wing paddles can even come out of the water slightly ahead of where they went in because of their 'lift" in the water. So the tip of the blade will only sweep out a distance equal to the change of angles of your paddle shaft during the stroke measured from that stationary pivot point to the blade tip. Since the center of power is even nearer to the pivot point than the blade tip you should see that your estimate of a meter of paddle motion is much too large. >>>>The position against-the-dock is introduced for two reasons: - - To check if there IS a position of rest to be found; - - To give students time to find that rest. There surely will be differences with actual paddling, but no differences that affect the purpose of the dock-exercise.<<<<<< Since with every reasonable kayak stroke there is a rest for the paddle hold up muscles I don't see why it needs looking for by a student. Okay, maybe if they are using what you call the "rental stroke". Please describe the rental stroke, as I'm not sure what you mean. The fiberglass rental kayaks I see often have the gelcoat worn off where the paddle slides across the deck near the front half of the cockpit. It seems some new paddlers a least have solved the paddle lifting muscles problem much like you did by supporting the paddle in the middle. The first time I went paqddling I had sore trapezoids the next day. I must not have used them much before because even if I didn't paddle for many months I have never had sore trapezoids from paddling since then. Or maybe I learned how to not need them to hold up the paddle after that first time paddling. I wrote: > BTW, I have no trouble going slower if that is what my paddling partners are > doing. I'm curious to hear an explanation as to why from those who seem to > have trouble doing that. Are you all using wing paddles (that just don't work > right at slow speeds) or is there some other reasons? Psychological maybe? Niels responded: >>>>If (and only IF) my hypothesis of using potential energy is valid, then _that's_ the reason. To paddle slowly, you'd have to keep that energy in check - by straining muscles that otherwise could be at rest.<<<<<< I don't see why you don't just take a rest between your strokes (at the end of a stroke) then. If the other paddles are going considerably slower than your 3 knot pace it hardly matters if your stroke is then less efficient because, as you yourself pointed out, just going slower is a more efficient way to paddle a given distance anyway. *************************************************************************** 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/ ***************************************************************************
MATT MARINER BROZE wrote: > Given your pivot at > the shoulder model and gravitational paddling theory, any resistance to the > blade (and even the falling of the blade before it meets water resistance) > throughout the stroke should allow the paddler to relax the paddle holding up > muscles except when lifting the hands and paddle out of the water to prepare > for the next stroke. It does. My new video, with measurements on the blade of paddle, confirms this. It might also answer your objections to my use of a suitcase. http://www.youtube.com/watch?v=io6S_gRxk8c > You must have very heavy arms or a really heavy paddle. My paddle IS quite heavy (1.3 kilos). I myself am quite slender, but also tall. I weigh about 90 kilograms. My measurement was not too accurate: I used a mechanical person-scale. It's not accurate to the kilo, but I _should_ have noticed a difference between 7 and 3 kilograms. I measured it several times over the last years. I agree (of course) that if your hands and paddle are that much lighter, you have much less to gain from potential energy. > Maybe you agree with > Derek H. who (at least years ago) advocated using a heavy paddle because he > felt it added "momentum" to his stroke. I'd think that a heavy paddle would give more losses in acceleration. Whatever stroke you use, you HAVE to change it's direction of rotation between strokes. There's no spring/pendulum/wheel mechanism to do it for you, so it has to be done with pure muscle power. I know a handful of polo-kayakers who use the lightest blades they can find - not to tire less or go faster, but to be able to react faster in putting a blade where they want it to be. I myself use heavy paddles strictly because they're sturdy and cheap. > So all the potential energy I'm going to get is only going to > be the result of half of what you are claiming for arm and paddle weight. > Furthermore, I think you may be also exaggerating the force by measuring the > middle of the paddle going up and down and using the weight of both arms for > each stroke. My new measurements in the new video should clear that up nicely, by measuring the force on the blade itself, in the direction that it would push water. I measure 3 kilograms of force on the blade, more or less consistent through the vertical rest. >Since it > is easy to do 3 knots with a low, elbows at the side,Eskimo type stroke > (driven by a small waist pivot) why keep working against gravity and wasting > more than half the energy you put in to lifting the paddle just so you can > teach a sprint racing stroke because that's what everyone else around you > teaches. Why not risk the ire of the governing bodies, who's main mission is > trying to train future racers, by pointing out how wasteful that racing stroke > is for those paddlers just wanting to put around at a nearly effortless 3 > knots. If I'm right, than the vertical-rest stroke is about as efficient as a low eskimo-stroke. To raise the blade, you mostly have to raise just one arm, close to the shoulder, which is a pretty comfortable move. We lack the data to draw a conclusion on the most efficient stroke. We'd _really_ need oxygen usage measurements of a greenland- and rest-stroke-paddler travelling at the same speed. If I had those data, and the eskimo-stroke turned out to more efficient, more comfortable and easier to keep up for a while, then I wouldn't hesitate to teach it. I'm quite well known for being a controversial instructor, within my own club and the wider Dutch community - but I only stray from the beaten path if I'm sure of myself. In this case, I'm not, and for now, I'm happy to follow the herd. > Do you agree that the power available to drive the kayak is whats left after > much of that potential energy has been disapated? Sure. Didn't we agree to call it 50%? > Since my potential energy available doing the same thing will be far less > than 30 watts (due to light paddle and arms) and probably far less than that > half that will be directed to moving the kayak I don't see of what importance > is a high potential energy if most of it will be later wasted and you had to > put an equal amount of kinetic energy into the system lifting the arms and > paddle to have the potential energy be that high in the first place. Your argument that most of the energy is wasted is true for ANY stroke. If most is wasted, then why paddle at all? The waste of my 30 watts of power is 50%; but so is the waste of your low greenland stroke. And, by the way: I never advocated to push the paddle higher to get more potential energy. I merely said: If you lift that arm anyway, then why not put the potential energy to some good use? > Even [during the last part of the "power" phase] it is retarding the paddle and the > paddle holding up muscles can be relaxed. I never thought any different. Miscommunication; no harm done. > (but before then the energy from > gravity will have likely been so completely dissipated that what little > residual energy is left is now having to lift water against gravity and will > have stopped the (relaxed gravity powered) stroke from getting that far > anyway. Yes. > I'm more confused than ever. Please provide a detailed description of what you > mean here. As best I can see you are using your upper arm to lift half the > paddle up against gravity to get the potential energy for the next stroke, but > your mechanical model has both arms falling down to power the stroke (and both > must be lifted on the model to set up the next stroke--sort of like a high > kneel canoe stroke). How do you do this with a sideways directed force? How do > your get up...from sideways? I'm really confused and need a much better > description of what you mean here. I hope my new video provides clarity. If not, I'm sure you'll let me know. > It seems to me that if the buoyancy bounce were timed > right, you could save your muscles from needing to accelerate the paddle as > much in lifting it against gravity. Some paddlers (including some of those who > like traditional native type wood paddle) like a buoyant blade and feel that > this helps them use less energy because of this rebound. It's an intriguing theory - but forgive me for not pursuing it at the moment. >> Niels responded: >> Back to my example-paddler at >> http://www.nibla.nl/tmp/paddlewise/ExampleStroke/ : >> In the video, there's little reference on the water or in the background >> to see how far the paddle moves. Judging just from the splashes, I'd say >> that his hands remain almost stationary above the water, but the blade >> underneath moves quite a bit (Close to a METER at the tip). > > You are wrong here. Am I? I think we actually AGREE here. Read on... > The stationary pivot point of a paddle during a stroke is > near the water's surface As I said... > So the tip of the blade > will only sweep out a distance equal to the change of angles of your paddle > shaft during the stroke measured from that stationary pivot point to the blade > tip. As I said... > Since the center of power is even nearer to the pivot point than the > blade tip you should see that your estimate of a meter of paddle motion is > much too large. ... which doesn't contradict my statement, but adds to it. I agree that the tip of the paddle, although it moves close to a meter, does NOT mean that the whole blade moves for a meter through the water. > Since with every reasonable kayak stroke there is a rest for the paddle hold > up muscles I don't see why it needs looking for by a student. Okay, maybe if > they are using what you call the "rental stroke". Please describe the rental > stroke, as I'm not sure what you mean. Hmmm... I can't really go out to the nearest rental and ask someone "You have the WORST stroke I've ever seen. Can I video it and put it on youtube?" So I'll do my best to describe it. The "rental stroke" is a very shallow stroke, with no blade ever fully submersed. It's more like stroking the surface than like putting in a blade an pulling on it. The motion is strictly made from the arms, with the center of the paddle in a fixed place, centered above the deck. The arms perform more of a cycling motion than a paddling motion. The fiberglass rental kayaks I see > often have the gelcoat worn off where the paddle slides across the deck near > the front half of the cockpit. It seems some new paddlers a least have solved > the paddle lifting muscles problem much like you did by supporting the paddle > in the middle. They try - but quickly find out that the deck is not a good support. Most rentals have large cockpits, so you'll have to rest it on the rims of the cockpit. The paddle will bump on those rims when switching sides. It also has to slide back and forth over those rims during the stroke, making it a noisy and destructive way to propel a kayak. > I don't see why you don't just take a rest between your strokes (at the end of > a stroke) then. To really REST a paddle, I'd have to put it down on the rim of my cockpit. Even in small waves, the blades will catch the water, pushing the paddle out of my hands, interfering with my course and slowing me down. Resting IS what I do though; but I keep the paddle in the water at the end of the stroke, and use it as a rudder for a couple of seconds. Note that I'm not complaining about my slow companions. I don't mind taking rests or practicing my draw-strokes, skulls and braces while they labour on. It's just an observation that, while paddling, I have a minimum speed. > If the other paddles are going considerably slower than your 3 > knot pace it hardly matters if your stroke is then less efficient because, as > you yourself pointed out, just going slower is a more efficient way to paddle > a given distance anyway. If we were paddling robots, paddling slower would always be more efficient - but we aren't. Just holding up a paddle drains energy. I see only two ways to not hold up the paddle: Rest it (as you suggested) or use the vertical-rest-stroke, which will only work at your minimal speed. Switching between those two is the obvious solution to paddle slowly - which I do. *************************************************************************** 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/ ***************************************************************************
My last video needs some notes: http://www.youtube.com/watch?v=io6S_gRxk8c - It's very hard to read the forces on the video. You'll have to believe me when I say that it quite consistently reads 3kg/30N. Then again: You'll also have to believe that I calibrated it without cheating, that I didn't fill my paddle with lead and that I don't push the paddle down to increase the measurement. There's only one way to be sure: Repeat the experiment for yourself. If you do, please share the results. - I've mentioned it before, but didn't mention it in this specific video: There's no such thing as FREE energy. Whatever comes out you'll have to put in first. - In my first video, I've made concessions into what to put in and what to keep out. I wouldn't go into heavy physics in it, but in the next version, I will put in this measurement. - Watch how Kira looks up at me, in complete trust and admiration. That's at least ONE creature that thinks I'm 100% right, always. 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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