Re: [PSUBS-MAILIST] No more gel-coat!

["Richard Gordon" <lrrg@wantree.com.au>]

Dear Gary,
                 An intact boundary layer is only of any benefit at the
kinds of velocities an aircraft travels at. You see even golf balls, which
are designed to minimize drag have dimples all over the skin to disrupt the
boundary layer and minimize drag. There are speeds at which an intact
boundary becomes necissary for drag reduction, but for anything below that
it needs to be disrupted.

The kinds of velocities you are likely to get out of a small submarine are
definiely within this range. I never really seriously suggested sand-paper
as the material for the job. It was only a flippant mention in that first
email on the subject. I did suggest a better way in the second email. But I
do know this to be true, the boundary layer must be disrupted.

Rich
----- Original Message -----
From: Gary R. Boucher <protek@shreve.net>
To: <personal_submersibles@psubs.org>
Sent: Tuesday, February 27, 2001 10:33 PM
Subject: [PSUBS-MAILIST] No more gel-coat!


>      I seldom post anything but often take a look in to see what is going
> on.  Now I am truly puzzled.  First, I am not a fluids engineer, but I do
> know some facts about aerodynamics from years of studying airplanes.  I
> think you fellows are talking about turbulent boundary layer.  As air
flows
> over an airplane wing the velocity of the air approaches zero as it comes
> in contact with the wing itself.  In an airplane an undisturbed boundary
> layer is very important.  This creates laminar flow down to the wings
> surface and greatly reduces drag.  One reason that the P-51 in WWII was so
> fast was that they could maintain this laminar flow well past a third of
> the wings cord.  The British gained advantage with this effect also until
> they started painting their Spitfires with a rough dull finish camouflage
> paint which disturbed the laminar flow and caused greatly increased
> drag.  Everything I have studied suggests that you want to minimize
> turbulent boundary layer flow to reduce drag.  I have no doubt that
putting
> something like course sandpaper on the hull of a sub would be a massive
> mistake.
>      Perhaps there is some finish that promotes a type of turbulent flow
> that is benificial but before anyone goes for the rough look I think you
> need to research this extensively.
>
> G, Boucher
>
>