Thom Stewart wrote:
Gary,

I believe most booms have enough flex in them to make a vang a
reasonable adjustment. I know mine does, and I have mid-boom sheeting.
Also a free footed main. So my vang is basically an anti lifting device
used off the wind but I can get enough bend to shorten the distance
between Tack & Clew to get enough increase in draft without adjusting
the out haul.

The leech does kind of go loose as I go off the wind. I lose the upper
part the main. I've been known to add the preventer to act as a barbar
hayl to reduce the twist and get the tell tales flying. (One man's
observation)



http://community.webtv.net/tassail/ThomPage

Thom,
I think that the terms "end boom" and "mid boom" are too vague. The
mid boom sheeting is rarely mid boom and some times quite close to the
end. Mine, for example, has about 30 feet of boom ahead of the sheet
and 5 behind on one boat and on the other the proportions are about the
same.

All vangs are antilifting devices. They are supposed to start working
where the traveler becomes less efficient. Of course the pressure on
the sail is different when running and the boom may lift a little unless
the vang and boom are very strong and flex free. Different aerodynamics
- wing versus wall. I use my vang as a pre-vang by running it to the
deck at the shrouds and can keep the leech very tight.