I don't think there is much of a difference in the effectiveness of
the two types, provided there is a shelf, if attached to the boom -
and I haven't seen a new main without one for many years.

I once read, that one of the reasons for the "America's" good windward
ability was, that it had a flat main, that was lashed to the boom -
but that was a rather large cotton sail. In this case, I imagine, that
it might help to sacrifice the shape of the lower part of the main to
gain a flatter sail further up. With modern cloth (including dacron)
this trade off seems to be a bad idea.

Assuming it is slightly cheaper to produce a loose-footed main I would
expect that they will gain further popularity.

Since the boom-height is often is decided in accordance with
head-height, it might be possible to gain a bit of area by lowering
the middle part of the foot since the foot in it self will not damage
your head as much as the boom might do.

The question should probably be answered after thinking through the
consequences for the edge-flow and vortex at the foot. The shelf might
have a endplate-effect, but I imagine, that this is cancelled out by
the slightly larger effective area, that is possible with a loose
foot.

Maybe I should ad, that this poste is more loose thoughts than
knowledge.

Peter S/Y Anicula

Thom wrote:
Bart,

I use a loose footed main. I like it because I can carry the shape
of
the sail all the way to the foot of the sail. I had used a shelf
with my
other main and thought that was the way to go but my present sail is
completely free and I"m damn if I don't like it better. I do believe
it
is faster and that is probably because of the ease in shaping the
sail.
A bonus is access to both sides of the boom from the top of the boom

Adding a shelf is easy. Adding a bolt rope footed main is a
different
ball game, I do believe