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/ ***************************************************************************Received on Sun May 01 2011 - 08:10:03 PDT
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