Rich wrote; >I will be happy to take this bet, provided the phrase "forward stroke" is >changed to "correctly performed forward stroke", since of course it's >possible (however undesirable) to take a poor stroke and move the paddle. I don't think it matters what kind of stroke. Any stroke you choose that develops forward thrust should do. To keep things simple it would be best to perform your tests and proofs in deep water so there is no influence from the bottom and in clean non moving water at 59 degrees F so it will be easy to see that it is the paddle alone that is causing the observed phenomenon and that raw sewage or ice are not influencing the results. All that is needed for proof is to do the demonstration before impartial observers and the only evidence they need is that the boat was propelled forward but there was no turbulence around the blade to indicate motion. You might want to film it and be sure you can repeat the experiment so we can present it properly to the Nobel Prize people. ;-) Quite simple really. I suggest one attempt it first before accepting any wagers. :-) This discussion is in danger of becoming overheated. I recall Rich's statement was that the paddle does not move. I don't think he said that it only moved a little. Correct me if I am wrong. The statement as I recall it is inconsistent with the physics of fluids that I understand (and, of course, I could be wrong and often am) For example. fluid (fl”“īd) noun Abbr. fl, fl. A continuous, amorphous substance whose molecules move freely past one another and that has the tendency to assume the shape of its container; a liquid or gas. Excerpted from The American Heritage® Dictionary of the English Language, Third Edition © 1996 by Houghton Mifflin Company. Electronic version licensed from INSO Corporation; further reproduction and distribution in accordance with the Copyright Law of the United States. All rights reserved. This may not seem enlightening but I think it is. A fluid flows from an area of high pressure into an area of low pressure seeking equilibrium. When you apply pressure to the paddle blade there is a pressure differential between the front and back face. On one side it is higher than on the other side and the water wants to flow from the high pressure side to the low pressure side. This pressure differential can only occur if there is motion. A stationary paddle has no pressure differential. Three is a simple experiment to do at home. Fill your bathtub with water and then try to move your paddle through the water. Even if you apply only the smallest amount of force you will see that it moves and that the water flows around the edges of the paddle. No matter how you angle or twist the paddle you will find you cannot apply force without motion. When you are in a boat the force developed propels the boat. The speed of the boat depends upon the drag of the boat and the force direction of the exerted by the paddle. Now, people often assume that, because the motion of the paddle is small there is no motion mostly because it isn't really obvious. Why isn't there a lot of motion? The reason is that the force developed is a function of velocity, area, drag coefficient and fluid viscosity. We can ignore viscosity and deal only with the first three. The simplified equation is force = Cd * A * V^2. The important thing is the v^2. Twice the velocity produces four times the force. So, a fast hard pull on the paddle produces an enormous increase in power generated even though the duration and hence the distance travelled may be small. Note that there is nothing in the formula for distance travelled. Notice also that if velocity equals zero there is no force at all. Of course, if the drag coefficient and area are low then there may be considerable motion involved in achieving the same force. I suspect that Rich has observed (like so many people) no visible movement and concluded that there was no movement. I think this is an easy mistake to make particularly in moving water when it isn't always clear what is moving and when. It was expressed (by someone can't recall who) that it was a wonder that narrow paddles create force at all. Not so. Anything moving through the water creates a drag force and sometimes a lift force. Whether the force is a positive or negative thing depends upon your objective, The drag of the boat is negative and the drag of the paddle is (much of the time) positive. I have personal experience paddling a canoe with a pole and anyone who has watched Harry Rock do it will be amazed at the speed he achieves. No magic just velocity and drag at work. Can an infinite number of monkeys using an infinite number of pencils paddle a boat at an infinite speed? :-) At times we argue at cross purposes. For example, many people assume that all modern paddles are flat plates with no airfoil. Such is not nor need not be the case. It is often done as a flat plate for the economies of production (also sometimes they seem to work pretty well). Many home made low aspect ratio blades are foils and some of them quite good foils. It may be true that some modern blades do not perform in certain ways as well as most high aspect ratio blades but there is the difference between "some" and "all". To me it seems this is the crux of a lot of this debate - the comparison of some Greenland paddles with some modern paddles and drawing conclusions for all from a comparison of some. Steve writes. >Take your eyes to your TV and look at what they're doing. It certainly >looks like the paddle is staying put--OK, maybe it moves a >centimeter--and the boat is moving. But unless the bouy is also moving >through the water, the paddle is pretty well fixed. In this Steve is quite right. It doesn't look like they move a lot nor do they move a lot but they don't have too. Movement is movement and the movement is essential to developing thrust. Do you recall watching the old western movies and the wheels of the stage coach looked like the were standing still? Certainly looked like they didn't move. Not a fair analogy in this case but one must be careful with what we see. The issue here is not how much the paddle moves but does it move. Rich was quite clear about this. I think that if one thinks a bit about what a fluid is one can see that, since a fluid cannot support sheer forces the paddle has to move even at very small forces. Do not confuse the terms "support" and "resist". The internal forces in the fluid resist sheer (van der Waals forces?) but that is not the same as "support". Granted Rich's field is quantum mechanics and that may be the problem. Perhaps he has confused water with Shrodinger's cat or is it Heisenberg's Uncertainty. :-) Obviously quantum physics isn't my field :-)))) Just joking here folks. Don't get shorts in a knot. Kevin wrote; >One is that 'efficiency' needs to be broken down into absolute >power output from the paddle, versus the ratio of paddler power input over >paddle power output, where the latter is my definition of paddle >efficiency. The former is of interest to flatwater sprint kayakers where >speed is all that matters, the latter is of interest to recreational and >marathon sea kayakers where stamina and efficiency over long distances are >key. This doesn't appear valid. Why wouldn't racers be interested in getting more efficiency? Granted they want it at higher outputs but they want as much out of what they put in as they can get, No? Why would they want or not care if they got less? >Technically speaking, even a flat plane is an airfoil, as is a cylinder or >sphere. However the angle of attack window which does not produce >turbulence is much much smaller for a flat plane than for a foil shaped >paddle. A greenland paddle makes it much easier to maintain laminar flow >and therefore maximum lift during the entire stroke. I don't know how easy >this is with a flat blade, or whether it is practically possible. Does not this return to my original comment that there was no reason that a low aspect ratio blade (I am getting tired of typing that so will use LAR from now on) can't work the same way. In other words is this not an question not of whether the paddle is HAR or LAR blade but whether or not it has a functional airfoil shape? . >The greenland paddle is a wing, period. However some of the strokes used >have a different form than modern racing wing technique, and therefore the >lift and drag vectors may be different. This seems to be the case but is the any reason that anyone can think of why all LAR paddles are either flat plates or wings? Why not a nice symmetrical foil? Sort of like my balsa wood paddle. >There is enough lift generated to make the paddle leave the water >technically farther ahead of the point that it was planted. There have >been video studies that proven this, I have heard from racing friends. >Greenland paddles can be used in the modern style of wing paddles... I >call it the "racing" stroke. I use it to accelerate to catch waves. Are you sure of this (first portion not using Greenland paddle like a wing portion). As the paddle is withdrawn from the water toward the end of the stroke isn't its forward velocity now closer to the boat velocity and so it may be drawn past the insertion point rather than having lifted past the insertion point. Maybe it is a combination of lift and the boat velocity but I would question that it is the lift alone that causes the observed phenomenon. Interestingly enough Taylor shows that phenomenon happening with paddle wheel floats where the floats are flat plates. Even with my flat blade paddles I get the same result at certain speeds and paddle immersions. Trying to recall an earlier discussion on this phenomenon that probably took place on WaveLength. Cheers, John Winters Redwing Designs Specialists in Human Powered Watercraft http://home.ican.net/~735769/ *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.gasp-seakayak.net/paddlewise/ ***************************************************************************Received on Fri Jul 24 1998 - 09:16:15 PDT
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