Seat of the proverbial pants
Howdy, Mac's can be problematic to tune, as the wire size and configuration don't seem to correspond to usual rules of thumb. So we tend to squint our way through, and have done enough of them that our squinting has some validity on the water. So start by just getting the slack out of the lowers, getting the uppers and backstay a couple of turns tighter, and try it out, in light airs. Monitor mast shape and the leeward shrouds, taking up on both sides as required. In other words, tune like everyone did before those handy gauges came along. Remember, you're not trying to match some set of numbers in a manual; you're trying to keep the mast straight, keep it from going any further than necessary to leeward, and keeping the jibstay as straight as practicable. At risk of being self-promoting, I must recommend our rig tuning video, which will accquaint you with the basic principles that will help this all make sense. Fair leads, Brion Toss
