by GreenLake » Mon Nov 16, 2020 11:07 pm
The maximal static loads on the rigging are given by the capsize limit. (Any more force than that in the sail, and you go over anyway).
For a halyard that would be something like the original tension in the sail, plus the entire sail force assumed to act on the halyard (we're trying to estimate limits, so we take the worst case). Your supersized 600# of skipper+crew can get their COG perhaps out 4 feet from the center line or 5 feet from the one part of the hull still immersed as you heel the boat; the center of the mast, as seen from the sail is about 15' up, so 5 x 600=15 x sailforce, which comes to about 200# at the limit. More than that, and you go over. WIth 50# of pre-tension in the rig, you are at 250#.
There's very little sailboat hardware that isn't rated at least that (unless you go for the tiniest sizes).
You will encounter dynamic loads that are less easy to calculate. So, make up a safety factor. But I would think that sheets are more likely to see shock loads, e.g. in a patent gybe.
Whatever your calculation, look up what diameter rope you need to get a mean working load (MWL) of 500#. Almost nobody goes that small, although I have another boat rigged with 3mm halyards. So sizing blocks by what loads your lines can handle would mean that you are grossly overdimensioning your rig.
For example, 7/64" or 2.5mm Amsteel Blue has a "minimum strength" of 1400 lbs -- if that is supposed to be the breaking strength then the MWL would be about 1/3 or 450lbs. However, you don't want to use blocks rated at 1400 lbs. (One reason you overdimension your running rigging, other than handling, is chafe - so that even before you can detect and correct any damage, the line will still hold what it needs to).
(I'm happy for anyone to check these assumptions and my math. If you want to know how the pros are doing it read "Principles of Yacht Design" by Larsson & Eliasson).
~ green ~ lake ~ ~