"Glenn Ashmore" writes:

Just reading up on golf ball dimples They evidently create a thin layer of
turbulence that keeps the laminar flow from breaking away longer reducing
the turbulent area behind the ball. Discounting the Magnus effect because
a hull does not (normally) spin, the result is less drag.

That said, it seems to follow that dimples on the mast would hold the air
flow around it further aft reducing the turbulence on the luff of the main.
Probably not much but then the big racers cut their toothbrushes in half...
:-)

Alu spars for monohulls used (I haven't checked this in a while) to
have a few riblets about one fourth down-stream on each side to trip
the boundary layer to stop von Karman vortices from forming. This reduces
the separation bubble on the suction side of the sail and reduces
the risk of spar oscillation in harbour.

Another approach is of course to make sure the spar contribute
to drive rather than to drag: a rotating wing-shaped spar.

--
Martin Schöön

"Problems worthy of attack
prove their worth by hitting back"
Piet Hein