Mike wrote; > These two definitions leave out a several paddles that I would not > classify as Greenland - specifically, the composite quill paddles. They also leave out John Brand's twisted Greenland paddle from the 19th century (supposedly). Shows how difficult this kind of thing can get Rob wrote; > Not entirely true. The blade produces a force that has a component in the > forward direction, also one across the boat. The force is produced by > flow across the blade, from one edge to another. On an airplane, with > more or less horizontal foils, the components of the force produced by a > foil are called "lift" and "drag", one vertical and one against the > direction of motion. For a paddle, we must break the force into slightly > different vector components, with new names, as we are not trying to > support a heavier-than-air craft, but push a boat. I suggest we call the > forces components "drive" (forward) and "cross-boat". No need. Lift remains lift and drag remains drag. You need only resolve the directions in which the forces act to determine if they provide driving force in the direction desired. Having said that I still prefer the term "Thrust" with regards to the total force acting to propel the boat. > My stroke is nearly vertical. There is no downward component to the force. Does this mean you insert the blade tip into the water and then push it straight down beside the boat? Snip > I don't believe that my stroke is optimised to make use of this effect. > Resources on the Web note that Maligiaq emphasizes the importance of a > long follow-through, and there is anecdotal evidence of this push from > related sources. How good is anecdotal evidence? Would you trust it coming from a large drug company? > The Greenland paddle is well designed to create a low pressure zone deep > in the water to avoid ventilation. That is why the blade is wider at the > bottom, and the tapers to a nearly round shape at the surface. The shape > produces a blade with a high aspect ratio and which has great resistance > to ventilation. But not stall. If you rely on lift as the driving force then resisting stall becomes more important. With any paddle using drag as a large portion of thrust resisting ventilation becomes a matter of full immersion and reducing the loading per unit of area. If you get ventilation you might want to ask if you really do use much lift. > It may not be "lift" we are using to drive the boat, but it is definitely > a force produced by flow across the blade, and the drive force produced is > higher with this flow regime than when the paddle is dragged through the > water at 90 degrees to the motion. I suspect that playing with the > variables that improve lift will increase the drive force as well. ????? Can you clarify this? Also, I wonder why you have compared the flow over the Greenland paddle to one that acts at 90 degrees to the direction of travel. Cannot other paddle types have an angle of attack? SNIP > I have often wondered if John Winters' experiments with paddles used angle > of attack as a variable? Strange things happen when the blade tilts, as > he points out! Yes, and nothing strange at all. I could detect only two important components, lift and drag and we need only resolve their directions of action and magnitude. I used the term "magic" in a facetious sense hence the smiley. Cheers John Winters *************************************************************************** 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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