G'day Niels, Something that's puzzling me is that the potential energy of a falling weight is directed vertically downwards and the kinetic energy will not be converted to forward movement unless it acts against a deflecting force as it might in your invention. So I can see that your invention might work albeit probably with a very slight mechanical advantage. However, if your arms move horizontally as they fall to provide the deflection they will be doing work to propel the kayak. Alternatively if they are static as your arms fall they will both provide a braking force to the blade in the water and consume energy as the muscles are continually triggered faster than their relaxation time to maintain position against the braking force. A double inefficiency. Its late here so I may not be thinking straight but happy to hear it explained. All the best, PeterO *************************************************************************** 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/ ***************************************************************************
PeterO wrote: > Something that's puzzling me is that the potential energy of a falling > weight is directed vertically downwards and the kinetic energy will not be > converted to forward movement [...] If I had answered that question in my video, it might have saved me half of the objections. Thanks for asking the right question. While the arms move downward, the paddle-blade does not. Assuming you keep you elbows locked and move your arms down from the shoulders, both your hands and your paddleblades will travel in a circle around your shoulders. I made a drawing: http://www.nibla.nl/tmp/paddlewise/halfway.gif You see that, while the hands are moving down, the submersed blade is mostly moving backwards. The force that the paddle produces is not in the same direction as the movement. We all know that it takes very little force to slice a blade through the water - anyone who tried to brace on a vertical blade has experienced it. The main force that a blade produces is always perpendicular to the surface of the blade. We use that characteristic in all our rudders, draw-strokes and sculls. As shown in my drawing, halfway through the vertical-rest-stroke, the force is almost perfectly backward - as long as the blade is vertical in the water. The beginning and end of the stroke are less efficient, as shown in another drawing: http://www.nibla.nl/tmp/paddlewise/begin_and_end.gif It nicely shows why you shouldn't make your stroke too long at the back. > So I can see that your invention might work > albeit probably with a very slight mechanical advantage. My invention was never meant to make use of the gravity-stroke. I simply analyzed my own stroke from video, looked for the place of my arms and paddle with the smallest amount of movement, and thought that would be the best place to support the paddle. I noticed that there's a spot, in front of me at the height of my chest, where the paddle always moves through, so I made a support that allowed that movement. It's quite clearly visible in a small animation on my website: http://www.nibla.nl/peddeldrager/ (scroll down to the moving pictures) It was long after designing the paddle-carrier that I thought up the vertical-rest-stroke. I'm happy to note that my invention extends on the same principle, but it's coincidence. When watching the animation from my link, I see the center of my paddle rise and fall for about 30/40 centimeters, once more indicating about 20/30 watts of power from potential energy. I maintain that most of the energy is going into backward force and movement, having nowhere else to go. *************************************************************************** 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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