Do I wetsand or not - Gel Coat

Discussion in 'Powerboats' started by kwhydro, Oct 23, 2007.

  1. kwhydro
    Joined: Oct 2007
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    Location: Cleveland, Ohio

    kwhydro New Member

    Hello everyone, I'm a newbie to this site. Sorry about having it in this forum, tried to move, no luck.

    Question, I just finished spraying a waxed gel coat on the whole bottom of my Hydrostream which is upside down on the trailer, made it a lot easier. Anyhow, the orange peel from the gel coat is very light, Do I really need to wetsand it? The orange peel makes me think about my older Hydrostreams that had a sprayed color over the woven roven material on the outside, not like the newer totally smooth surfaces on hulls. Is there any proof of speed being lost due to very slight orange peel? It looks great to me, a couple of my boating buddies are coming over for a wetsanding party if needed. What do you think?:confused:

    Thank you, kwhydro

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  2. fiberglass jack
    Joined: Dec 2005
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    Location: toronto

    fiberglass jack Senior Member

    seeing that u used a wax in the gel it should sand ok dry, get some 3m sanding guide coat its a black powder that u rub over the hull it will leave all the divits in the gel black just sand till they are gone and you will have a smooth hull with out the threat of a break through, a little more dusty.
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    A reasonable argument can be made that you'll be faster with a well orange pealed surface then a smooth one. Golf balls have dimples for a reason. Bumps (like orange peal) are better then dimples too.

  4. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    The guys who tune ultra-high-performance jet skis have been known to run longitudinal scratches in the underside with 60-grit sandpaper. There are cases where forcing a turbulent boundary layer in this manner is beneficial. It depends mainly on the pressure gradients and Reynolds number regime in which the hull operates; there are mathematical ways to guess whether it's worthwhile to have a textured or smooth surface, but trial and error with models is what it usually comes down to in practice.
    (A golf ball operates in the regime of Reynolds number Re=10^5 ; a typical planing boat is around Re=10^8 at the transom. The dimples on a golf ball serve to force a turbulent flow where it would naturally be laminar; the boundary layer under the boat is already fully turbulent.)
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