by Roger » Fri Mar 20, 2009 9:44 pm
Ideally, you want the attachment point on the bottom of the boom as far our as it is down from the boom. You want to maximize the angle, so placing the bottom of the vang just an inch or two above the deck (as low as you can go) will determine the same distance out from the mast on the bottom of the boom. Here's the problem however: The ideal 45 degree angle is not a big triangle, so you may want to push the upper leg of the triangle a bit further along the boom. As you do so the boom fang angle gets a bit shallower, but about 2' out still works.
My mast was shortened by about 6" following a knockdown so my angle had to be shallower. If I recall correctly the distance from boom to deck was about 20" but my distance out was just over the 24" mark.
The good news is that the stressors on the boom vang are not that great and any 3:1 rig with 1/4" line will work for the forces at play here. I have some pictures of my setup if you wish to see them. e-mail me at roger02 att mts dott net and I will send them to you.