Joe,
I don't have an answer, I hope someoneelse may have it for you. Here is what I can throw at you if all else fails.Is the mast up or down on the boat?I am assuming that you do not have a furling system.If you have a furling system, it can be different with every boat.If your mast is up tie a piece of rope to the halyard to the mast head and the loose end to the tack. Mark the tack, pull it down and measure it.If the boat has the mast down, the forestay could be measured.If you are buying a sail, note shackle and splice length. You don't want a sail that causes the splice to enter the mast head.If you do not want a deck sweeper, account for a pennant to raise the tack off the deck.If you are buying a sail, most sailmakers have the standard dimensions.I hope something here helps, r.w.landau