Re: [Paddlewise] Pygmy Coho, multi chine

-----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


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