"Bart" wrote in message
ups.com...
I've had one in-mast furler jam and it took lots of
playihng with it to get it to furl. Consider what a
have furled in mast sail will do when the wind picks
up.

Yes, they are fine when they work but if they do not work you have big
trouble. In a foresail the sailmaker can cut the sail to allow for the
inevitable sag in the forestay. My boat has a Mack foresail which sets
beautifully when unfurled and also has padding so that it also furls neatly.
But a furling mainsail is constrained by being held within the mast. The
foil on which the sail is rolled wants to sag in the middle like a forestay
but it cannot. So, it sags as much as it can until further sag is resisted
by friction between the sail and the slot from which it emerges. So there is
always friction between the 'canvas' and the slots in the mast which is
going to cause wear on the stitching and constant maintenance and there is
always the possibility of the whole thing jamming.
Since it is unlikely to jam while already furled it is most likely to jam
while halfway back in and if you are caught out in increasing wind you will
have real problems.
So, for me, conventional reefing and lowering of the sail is the way to go
for serious sailors.
Just my 2 (kroners, pence or cents) worth.