My 4:1 preventer tackles also act as a vang. They are attached to a bail on the boom about a third of the way aft, and to a big shackle whose pin secures the aft lower stay. Line leads aft along the rail to a cam cleat on the cockpit coaming. They completely eliminate the chance of an accidental jibe. I use single braid line and am not too worried about shock loading as my boom is pretty high.