Hi Matt, I replied to a post of Peter first, with some drawings of the actual movement. That might satisfy some of your objections. If not, please let me know. Please read that post first (if you haven't done so already); I'll use those answers to answer your questions. MATT MARINER BROZE wrote: > If you use your patented roller device to hold up your paddle for you, aren't > you defeating your having gravity help you move forward? I don't think so: The center of my paddle moves down about 30/40 centimeters while rolling over the device. About 20/30 watts of energy is going... somewhere. To put force on the blade I think, so pretty much into moving the kayak. > Are you aware that some Eskimos use their front deck as a support for a heavy > paddle and at least some of the time use the same sliding stroke you use to > keep the paddle and arm weight supported? No, I didn't know that. Thanks for telling. > One inventor hangs his paddle from a > cord from a "crane" that arches over his head from the back deck. Yes: I've seen his contraption when doing my patent-research. I even saved the link: http://www.google.com/patents?id=vL0pAAAAEBAJ&printsec=abstract&zoom=4&source=gbs_summary_r&cad=0_0#v=onepage&q&f=false I think it's overly complicated, inconvenient and dangerous with all its dangling wires and supports. Apart from that, it might be quite comfortable - I've never tried. I don't think it can make use of gravity, but it doesn't have to. My opinion of the vertical-rest-stroke is: You put in the potential energy, so you might as well use it". In this contraption very little potential energy is stored, so the question of how to use it becomes void. > To someone putting enough effort into paddling to move their kayak near its > hull speed (which takes many times more energy than it does to move the kayak > at two knots--figure on doubling the effort for each knot faster you go) the > rest part of the stroke is when you have both blades out of the water not > during the power stroke. No argument here. If, during the power-stroke, you expend more energy than the 30 watts you spend lifting the paddle during the rest, it is rightly called the power-phase of the stroke. That's when you approach hull speed, which most people don't do, except for short sprints. My own kayak-club maintains a speed of around 3 knots, in various touring and sea-kayaks. Do you agree that about 15 watts should do the job for that kind of speed? > During that rest time you do lift one part of the paddle but that is somewhat > compensated for because you are lowering the other half of the paddle at the > same time so the effective weight is about the weight of the paddle In all my measurements, I looked at the _center_ of the paddle, which I assume to be the center of gravity. > are only having to use the trapezoid (neck to shoulder--hold up) muscles for a > very short period of time because you don't want to let the kayak slow much > between strokes because accelerating the kayak again requires a lot more > energy than maintaining a given speed. Matt, come on! The slower you go, the more efficient you are in energy per distance. So, the more often you let your kayak slow down, the more efficient you get. Just accelerating and decelerating doesn't cost any energy, unless you put on the brakes. Look at a weight on a spring: It keeps bumping up and down forever. Once a blade is in the water again you > aren't having to hold up the paddle with the trapezoids (which is one reason > you can paddle a lot longer than you can simply hold up a paddle). So you think the "vertical rest" is a valid principle, at least for those specific muscles? Since those muscles tire the most quickly in my students (and myself) it's worth pointing out a way to give them some rest. I skip part of your post that's strictly about moving near hull speed. All you say is valid at high speed, but not at the speed that I'd like my students to adopt in their first lessons. It's also not the speed I strive for myself. > Your "vertical rest stroke" does rest you from having to hold up the paddle > with the "hold up paddle" muscles (as does any stroke) Any _good_ stroke, I'd say. The rental-stroke supplies no such rest. > but you are still using > other muscles to hold up the paddle (unless maybe you have your patented > device or a very buoyant blade that floats the paddle and arms with just one > blade in the water). 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've not yet seen such a buoyant blade paddle and though > it is theoretically possible, I suspect there would be major disadvantages or > compromises to it. I don't think it would work. I paddle in shallow water sometimes, where I put my blade in the bottom and push myself forward. It's very awkward, and not just because of the increased drag of the kayak. It's just very uncomfortable to keep your blade at a fixed depth in the water. > Paddling against a dock is not a good representation of what happens during a > stroke because when the boat doesn't move the paddle must be pulled through > the water rather than remain planted rather solidly in the water while you > pull the sleek (compared to a paddle) kayak through the water. If I put force on a paddleblade in the water, it will drag through it. The blade doesn't know or care whether there's a kayak and whether it moves: When there's force, a blade will drag through the water. Always. As I say in my video: Against a dock, the stroke will take more time, giving a better feeling of the "rest". Apart from that, there's no real difference. *************************************************************************** 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 Fri Apr 29 2011 - 10:54:15 PDT
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