Hey Don,
If you are going to use the sidestays to keep the rig from falling forward, then the dimension you are worried about is the distance aft of the mast. The closer you are to the mast (fore/aft) the mode load will come into the stays when the rig is loaded forward. Th further back you are, the more your loads will drop, but as you noted the boom will not swing out to 90 degrees.
You will note that most of the sailing craft from that era had very substantial sidestay systems comprised of 5 or more sets of shrouds (with the netting strung up between them for climbing). My memory from most of these boats was that the aft set was substantially aft of the mast. Also many of the boats had the rig raked back which will help the geometry as well. They also had keel stepped masts so the deck was helping to hold the mast from crashing forward.
I’m not sure how they arrive at the comprimise. Schooners were a different breed from the square riggers. Square riggers were designed to run downwind in the trade winds. Schooners were designed with more abiluty to sail upwind and on reaching headings. So they were probably not overly concered with getting the boom out to 90 degrees for running downwind. Remember too that these are generally work boats (trade), not racing machines. So if they lost a 0.5% of downwind speed because the boom would not swing all the way out, they were probably not too concerned. It would cost them so little time in the grand scheme of things that it really would not matter.
They were more concerned about surviving the ocean storms. So the rigging was often overdesigned.
Beyond that, I’m not sure I can offer any specifics…
- Will
Will Gorgen