Originally Posted by ctl411
I think he is talking about "dumping" the vang when overpowered by a gust. Some race
boats now even have a "panic" button on the floor by the helm. Boat goes into a broach step on the button and it frees up the weather helm.
The vang tensions the leech directly, unlike the sheet, which hauls the boom inboard as well as tensioning the leech, but in varying proportions depending on the boom angle. So when the boom is outboard
of the end of the traveller, hardening up the sheet will haul the boom inboard more than it adds leech tension, and more and more the further outboard
the boom is. With the vang on, the sheet has less effect on leech tension (since that is already tensioned), and you can use it more for controlling angle of attack of the sail. Together with with the traveller, of course.
The traveller, analogous to the vang, acts directly on angle of attack without any effect on leech tension.
So with the new sails, I find myself making gross adjustments with the sheet, but then leaving the sheet alone, and using vang and traveller for adjustment of leech tension and angle of attack respectively.
Use the outhaul
at the same time as the vang if you're making the sail fuller or flatter.
Leech tension is one element (together with outhaul
tension) of sail fullness or flatness, but it also determines twist. If leech is tight, the sail doesn't twist as much. Slack the vang (or mainsheet if you're close-hauled), and the sail will twist off at the top.
So you don't have an unconstrained choice of full vs flat; you also have to consider twist, which can't be controlled independently.