I clicked on one of our sites sponsors as I always do when I am on, (your welcome Richard) and it was sailboatowners.com. It is a site for running rigging. You select your boat, pick what you want and it tells you the recommended line diameter and most importantly length. I am in need of new spinnaker sheets and I confirmed in my mind at least that they should be 72ft instead of the 70 footers that I have.
Nice site.
Good Sailing
Dale