I am not a sailboat enthusiast but I am interested in how fluid
interacts with the surface
I encountered a brand new 33 ft racer on a trailer in a shop being
readied for water. Looking at the bottom of the hull, I noticed that
the surface in contact with the water had a painted pattern / texture.
(This textured surface may also be protection.
I am sure it can also be smooth and polished if need be.)

It seems that water would be turbulated. Would that not generate more
drag? Is there an other reason why the bottom is textured,
like preventing laminar transition drag?

If the above is true (textured surface), why not have the sides
textured as well, since the boat will be gliding through the water on
its sides for a good part of its racing life? If not true why not have
the bottom as smooth as the sides.
Enquiring mind would like to know.
Udo Rumpf

On Sun, 08 Jul 2007 07:04:51 -0700, Udo wrote:

It seems that water would be turbulated. Would that not generate more
drag? Is there an other reason why the bottom is textured,
like preventing laminar transition drag?

Most successful sailboat racers are fanatical about maintaining a
mirror smooth surface on the bottom, especially the leading edge of
the keel and rudder where most of the lift is generated.

The usual drill is to wet sand the bottom paint first with 220 grit
followed by 400. We used to start with an X shaped sanding pattern
using rubber fairing blocks, finishing with longitudinal strokes
parallel to the water flow.