Stillraining, the source with rig and sail dimensions for just about every boat out there is Sailrite.com. Look under the Sail Quoting tab, then type in Irwin. They will list all the boats under that name. They have yours listed as a 42, but it's a ketch and the rig measurements are the same, if I'm not mistaken. They are usually very accurate, but sometimes the may get models listed wrong. I had an old Ericson that had a mark 1 & 2 version. You had to know the I,P,E, and J to figure out which model you were looking at. Take a look, again, I'm pretty sure this is your boat. Sailrite has a wealth of information for anyone trying to compare sail areas for different boats. Hope this is some help.
Will do... thats one of the few I didnt check..
and yes mine is referred to as as the 42 sometimes as its 41' 8" LOD but 45 overall and thats what the J mesurment would be calculated out to include the sprit.