> From: rebyl_kayak_at_energysustained.com > Something I'm still struggling to understand is why the Pittarak turns more > easily upwind with a reverse sweep and more easily downwind with a forward > sweep. The centre of rotation (if that's the right term) must be quite > different between the forward and reverse sweep. I've started trying to > develop an equation of motion treating the kayak as a single line with > points of contact at butt, knees and feet. One problem is how to make enough > realistic assumptions to reduce the variables. In particular how to > partition the forces between each point of contact and also to assign > realistic ranges of value to the relative angular velocities of the boat and > paddle with respect to the water. A friend commented I wouldn't get an > explanation with this approach as it was more likely to be related to wind > wave action but I find that just as hard to understand. You didn't say if this is when the Pittarak is starting from a standing position or when it is moving forward. If when moving forward, try it again when you are paddling backwards. I suspect it may now work the opposite way. Also try this without any wind. Next try to separate the effects of the wind and the waves. Maybe use boat wakes for no-wind waves and an offsore wind that hasn't had enough fetch to build waves yet. You also didn't say if you are leaning the kayak during these turns (if moving forward). If so are you leaning them exactly the same? Or perhaps you are leaning inside with the reverse sweep and to the outside with the forward sweep? That will change things. I think you can quit worrying about your points of contact with the kayak and concentrate on the kayaks pivot point (which changes with speed due to the resulting water pressure differential on the hull from front to back) and where in the water the paddle blade is acting. You will also have to take into account how your weight shift (to put the paddle blade where it is acting) may be affecting your trim and what change that trim change will make to your center of rotation. Leaning forward will move the center of rotation of the hull forward and visa-versa. If you give me a more detailed description of the conditions when you experience this (and just how you make these turns) that addresses my confusion I'll try to figure out what might be happening. *************************************************************************** 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 Mon Jun 14 2010 - 04:31:07 PDT
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