Mike Daly wrote: >>>>>>>On 23 Sep 2004 at 8:36, Gordin Warner wrote: > If the theory is correct a SOF kayak should enjoy a positive gain from > the indentations along the hull. I suppose the size of the > indentations might have a negative affect on this. The size is critical. It is also related to the velocity of the fluid along the surface. Golf balls have small dimples and move quite fast. SOF kayaks have relatively smooth changes over a large scale and move slowly in the water. I doubt that the shape changes in the SOF have a significant effect on the flow. BTW, aircraft floats operate by planing, not displacement (well, as you get anywhere near take off speed), so I doubt the analogy is completely correct.<<<<< I couldn't agree more. Dimples on a golf ball work by delaying separation of the airflow around the back of the ball so that it doesn't have as big of a "wake" retarding it. They are only effective in a certain range of Reynolds's numbers (a relationship between the speed the length effected and the density of the fluid). If I recall correctly, when the Reynolds's number is the same, even though the other parameters making it up are all different, things work the same. Kayaks operate in a different range than golf balls. Also, not being blunt on the rear like a ball a kayak would not likely benefit much from the delayed separation due to dimples even if it did happen operate in the same Reynolds's number range. Choppy water lets a planing hull skip from wave top to wave top cutting friction, unfortunately for the theory, kayaks aren't fast enough to gain this advantage from chop except maybe when surfing down the face of a steep wave. Peter used the word "dead" to describe the rigor mortis of "stiff" kayaks compared to the squishy movement of a SOF in waves. wouldn't that make a partially inflated rubber ducky the ultimate in undeadness? I too often think some kayaks feel "dead", but having a much large base to compare from (I'm almost to 800 now) I have come to somewhat different conclusions than Peter as to the causes of a "dead" feel. To me things that contribute to a dead feel are: heavy weight (gear loads and heavy kayaks suffering from inertia), flexible kayaks (some of my energy is wasted flexing the kayak--rotomolded plastic, flexible SOF, and inflatables come to mind), too much friction holding them back (kayaks that are too wide, too long, or poorly shaped), too hard to turn (stiff tracking kayaks with lots of keel at the bow and stern don't feel lively to me, those responsive to body English and paddle strokes do). Therefore, a stiff light carbon or wood kayak with a sporty and responsive feel paddled empty would be my first choice. A stiff SOF can be pretty good too but that floating dead cat flex of a soft one would be a negative rather than a positive. The softer the flex the deader it will feel. Think partially inflated inflatable or a dead jellyfish for the extreme. Things that are alive counteract the forces acting on them. A paddler is alive, a rigid kayak is moved by outside forces, does not actively resist them, but is also not changed in shape by them. A flexible kayak is like a dead animal that changes it shape when acted upon by other forces in the environment, including the living paddler. It tends to absorb those forces and dissipate them by flexing. Matt Broze www.marinerkayaks.com *************************************************************************** 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 Fri Sep 24 2004 - 17:37:20 PDT
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