Re: [Paddlewise] Graphite for Bottoms

This reminds me of an engineering course I took a while ago.  If I remember
correctly, fluid friction against a solid surface can be reduced if the
solid surface has some roughness to it.  The principle, as I remember, is
that a smooth surface allows laminar flow to occur near the wall, while a
rough surface creates turbulence near the wall.  The smooth wall (boat) has
to drag along a thick boundary layer of water, while the rough surface will
carry only a thin layer.  Similar to why dimples help a golf ball fly far.

So maybe roughing up the surface with sanding, or by creating a bumpy
coating with various fillers, could reduce drag.  Since I'm not practicing
hydrodynamic engineering right now, I have no idea whether this would work
or what size "bumps" are required.   Any ideas?

Doug Diez




>Mary wrote;
>
>
>>The Irish pub where hang out in Ft. Lauderdale is a center for the sailing
>>and yahting crowd. I ran into a fellow who designs racing hulls and he
>>stated that they use teflon in the gelcote. Then they sand it with either
>>200 or 400 grit to roughen it up. It was his opinion that an 18' kayak
>>should gain 1/4 knot with a similar sanding.
>
>
>Ahhh Yes, the old naval architect in the pub bit.
>
>Having been one of those I can say with complete confidence that the worst
>place in the world to get information on fluid dynamics is a pub where
>naval architects hang out.
>
>Cheers,
>John Winters
>Redwing Designs
>Specialists in Human Powered Watercraft
>http://home.ican.net/~735769/
>
>
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