daveu wrote: > There seems to be some feeling that the multichine hull goes a little slower than the hard chine (less seems). < Unless you are assuming rather poor fairing of the joints, this would seem to contradict the theory and beliefs that seem prevalent in the reading I've done on (mostly sailing) boats. A single hard chine is thought to generate a larger amount of turbulent drag than several less acute chines with much weaker vortexes, esp. when pithching in waves. I haven't sailed or paddled boats that were similar enough in other respects to judge this, but I have rowed traditional wooden boats that were fairly close in other parameters, and would attest that when hitting small, steep waves (powerboat and seaplane wakes), lapstrake hulls (essential many small, poorly faired chines) are slowed less than plywood hulls with only one or two chines. I would expect that the Coho would be a bit faster going to windward, but the Tern would surf faster coming back downwind. Mike Wagenbach *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
Mike Wagenbach wrote: >Unless you are assuming rather poor fairing of the joints, this would seem to contradict the theory and beliefs that seem prevalent in the reading I've done on (mostly sailing) boats. A single hard chine is thought to generate a larger amount of turbulent drag than several less acute chines with much weaker vortexes, esp. when pithching in waves. Ummm...back to Fluids 101. There is less friction in turbulent flow than laminar flow. There may be more _drag_ in a single chine hull than a multi chine hull that could make it slower, but more _turbulent_ flow would make the boat faster. Shawn -- 0 ____©/______ ~^~^~^~^~^~^~^~^\ ,/ /~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^~^ Shawn Baker 0 *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
-----Original Message----- From: Shawn W. Baker <baker_at_montana.com> To: Paddlewise <PaddleWise_at_lists.intelenet.net> Date: Thursday, August 12, 1999 12:29 PM Subject: Re: [Paddlewise] Pygmy Coho, multi chine >Mike Wagenbach wrote: >>Unless you are assuming rather poor fairing of the joints, this would seem to contradict the theory and beliefs that seem prevalent in the reading I've done on (mostly sailing) boats. A single hard chine is thought to generate a larger amount of turbulent drag than several less acute chines with much weaker vortexes, esp. when pithching in waves. > >Ummm...back to Fluids 101. There is less friction in turbulent flow >than laminar flow. There may be more _drag_ in a single chine hull than >a multi chine hull that could make it slower, but more _turbulent_ flow >would make the boat faster. > >Shawn You've gotten things backward. Laminar flow has about 4 times less resistance than turbulent flow. However neither hull is likely to have much of its area in laminar flow. The vortexes off the hard chines constitute separation drag which is much greater than turbulent flow drag. The question comes down to does one big chines vortexes cause more drag than more smaller chines vortexes add up to. Then if the single chine is less (which I don't know), is it enough to make up for the more wetted surface on the Tern? Only about 1% more but plugging in the numbers into Winters "Kaper" program (numbers that John Lockwood gave me) the Coho was about 3% easier at 3 knots and over 4% easier at 4 knots. The spreadsheet makes no judgements for vortexes from hard chines though. By the way this program/spreadsheet can be downloaded free or used at our website. Matt Broze http://www.marinerkayaks.com *************************************************************************** PaddleWise Paddling Mailing List Submissions: paddlewise_at_lists.intelenet.net Subscriptions: paddlewise-request_at_lists.intelenet.net Website: http://www.paddlewise.net/ ***************************************************************************
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