RE: My IOM won't go straight
it sounds very much like a helm balance problem.
when sailing it on either tack, as it heels over, does want to wander the same direction as the wind or does it want to wander into the wind ?
if with the wind, reduce the size of the jib,or increase the size of the main, or move the rig ahead. if into the wind, increase the size of the jib, decrease the size of the main, or move the rig aft.
most times, with a high aspect rig... as found on an IOM...., just moving the rig will balance it. you don't want any tendancy to to wander with the wind at all. a bit of windward helm is ok and a small trim on the steerage to correct it is fine, actually prefered. some trimming is naturally expected with a tall rig as the center of effort is high in the sail and has a greater lever as the boat heels, so different winds( and angles of heel) will need a different trim. the idea is to find the best rig position that has the least helm change in varying winds.