I have a nagging question that just hasn't yet been answered to my satisfaction. Why is roach in a mainsail a good idea?
I feel satisfied with the arguments of battens (full and partial) vs battenless, but the physics and benefits of a lot of mainsail roach elude me. I had thought that the roach was probably for rule beating purposes and would allow you to get a better PHRF rating by having a low measured luff but more sail area.
The problem with that theory is that pretty much all open class boats have lots of roach, especially at the head of the sail. There must be some specific benefit of roach besides "more sail area". I've also noticed that the wings of airplanes don't go to a point like a triangle. They have "roach" too.
So what does it do? Lots of roach seems to be at odds with the ultra high aspect modern rigs that dominate the races. If high aspect and all luff and no foot is the ideal, then why the roach?