Originally Posted by Faster
It's likely that your boom is plenty strong enough for the vang position you're describing, and a vang is a good idea in any case, but primarily for off the wind work. Once your sheeted in hard on the mainsheet, there's little for the vang to do if you're hard on the wind. Unless, of course, it's windy enough that you're into 'vang sheeting' (using vang for luff tension, mainsheet for 'angle of attack' only.. something you might try one day but does require a flattish main to be successful)
The vang while holding the boom down will also thrust it forward against the mast, helping to bend the mast and reduce the draft of the main.
halyard and Cunningham tension will help draw the draft forward on both the main & jib.
Outhaul tension will help flatten the foot and mast bend will flatten the rest of the main. The vang, and, if fractional rigged, backstay can do that.
Prebend can be set in the mast if you have spreaders that are swept back, more tension on the uppers will give more prebend. I know folks who say 'oh the yard set them right when they stepped the mast.' - Wrong - they didn't have a clue. At best, they centered the mast and guess at the rest (unless you have a popular one-design and told them how much pre-bend your sailmaker cut the main for). Racers who know their stuff will set rig tension every time they go out for the day's conditions. But that's a whole different thread, isn't it?