>Nick, >It sounds like you have never used a greenland paddle properly, so let me >answer a few things. > > ___________________ > > / Kevin Whilden \ > |Dept. of Geosciences \___ > |University of Washington \ > |kwhilden_at_u.washington.edu| > \________________________/ > >On Thu, 23 Jul 1998, Nick Schade wrote: > >> At 11:59 AM -0700 7/22/98, Julio MacWilliams wrote: >> > >> >The Greenland paddle flies through the water, the lift component that >> >is used to push the boat forward is more important than the side >> >component used by the drag of the blade alone. >SNIP >> >> This concept has been brought up before. The idea that the greenland paddle >> uses lift to propel the boat just makes no physical sense. The paddle just >> does not move far enough laterally through the water to provide significant >> lift. It, like most paddles is being used primarily as a parachute, not a >> wing. >> > >This is simply not true. I have a degree in physics as well, and it makes >perfect physical sense to me. The greenland paddle in its three main >varieties of strokes has a high lateral component of velocity at the ends >of the paddle. With the proper angle of attack and with a well constructed >foil shape, there is laminar flow across the paddle, and lift is generated >in the opposite direction of which the paddle is being pulled. Learning >how to make the lateral velocity of the paddle fast enough to generate >lift takes a fair bit of practice -- I can do it reliably in two of the >three kinds of strokes. Come to Seattle and I'll show you. Greenland >paddles generate lift. I think of lift as a force generated roughly perpendicular to the direction of motion. Like a wing flying horizontally gets lifted vertically. A force generated opposite the direction sounds like what an army parachute does, drag. I will defer to you, but when I said "lateral" I meant motion perpendicular to the direction of motion. > > >> Try paddling by only moving your hands up and down - no forward-backwards >> motion, no body rotation. In other words do your best imitation of a >> airplane propeller. You will be able to move yourself, but not as >> effectively as if you just pull. > >This is not the same physical scenario as a wing paddle. Now if you swung >your arms sideways out and in from the boat, with the hands cupped, then >it would be the same. Kind of a dumb concept however, because your arms >will never generate as much power as a paddle. I realize that most of the force created by a wing paddle comes from pulling parallel to the direction of motion. However, on the recovery, the wing-paddler swings the blade out wide, perpendicular to the direction the boat is going. During this phase of the stroke, the paddle generates "lift" as I currently understand it. Obviously, it would be dumb to try this with your hands. But if you were to do it with your paddle, this would be known as sculling, a perfectly reasonable thing to do. How fast can you make your boat go purely sculling? This is propulsion by lift alone. I do not beleive you in fact do this. Most good paddlers I have scene use some torso rotation and their hands move forward and back. This motion suggests to me that they are using a large component of drag with some lift to assist. > > > >> The greenland paddle is an efficient wing in long sweeps where the blade is >> slicing through the water. While paddling this is just the up-and-down >> component of the motion, which given, the low hand possition is >> intentionally small. Little motion = little lift => not much power. > >The paddle is indeed held low, however the hands are also held quite close >together, so relatively little vertical hand motion is needed to make the >ends of the paddle travel quite fast laterally. My paddle generates lift >as I slice it downwards, and then again as I slice it upwards. This is in >the high cadence "cruising" stroke that I defined in a previous post. > >> >> The wing paddle is much better at this. The paddle is pushed deep and then >> swung out to the side. There still is not a huge amount of lift provided, >> but enough to improve it's overall efficiency. >> >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. I guess I am picking nits. I will accept the wing paddle leaves the water ahead of where it enters, and if a wing paddle can, so too can a greenland paddle or any other paddle, however, what percentage of the propulsion is lift and what drag. Maybe we can not seperate the two, but John has numbers. If we take John's numbers as accurate. A "pure-drag" stroke is 86% efficient, and a wing paddle is 92% efficient, only about 7% (6/86) of the propulsion is provided by lift. Now lets assume the greenland paddle is twice as good at lift because it is really good. Still all you get is 14% of the power due to lift unless the paddle is not as good at drag. In the end it is probably a wash, but still lift is a small component of the overall efficiency. It may not be insignificant, even 7% is worthwhile, but I expect I could get similar results with any paddle, there is nothing magic about the greenland paddle in this respect. The stroke used with a greenland paddle can be reproduced with any paddle to similar effect. > >It's fun to talk physics regarding paddles. Cheers, >Kevin > > Nick Schade Guillemot Kayaks c/o Newfound Woodworks, 67 Danforth Brook Rd, Bristol, NH 03222 (603) 744-6872 Schade_at_guillemot-kayaks.com http://www.guillemot-kayaks.com/ >>>>"It's not just Art, It's a Craft!"<<<< *************************************************************************** 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 - 14:30:16 PDT
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