As I asked earlier; if you keep all the loads the same, same stay tension, same sails, same crew wt. etc. how does the mast know what it's attached to?

I submit that it doesn't.

The amount of lift generated by an A cat rig on an I20 platform may not fly the hull, but it won't just snap because it's on an I 20.

If it breaks on one boat, vs. another, you must have added more stress to it. So, how did you add that?

If you add a jib and a spinnaker to any A cat, the mast is not going to like it. If you do the same with a F18HT mast, it's not going to like it.

But those loads you added were up the mast, not at the base.

Wooter....! Splain it to them!

The act of flying a hull would relieve some stress, but if you put five 200lb. guys sitting on an A cat, not trapping, just sitting on the upwind hull, would the rig snap? No, you must overload it first by adding more...Wind. If the hull can't fly to relieve the added lift from more wind, then you have a problem.

You could argue that if you take an I20 with an A cat rig out in 30knots of wind, the mast will snap, but that's because the (heavier) I20 platform didn't fly a hull to relieve stress, as soon as the A cat would have, and that has allowed you to add more stress to the rig.

I doubt it would be a problem if you put the F18HT mast on the I20, as long as you also use the F18HT sail plan, ie. no jib, smaller spinnaker. I also doubt the I20 will be as fast as it would be, using it's own sail plan.

I'd love to hear from someone who actually knows what they are talking about, like Ben Hall and/or Pete Melvin, regarding mast design for hull wt. etc. I think it comes down to compression loading, as to how much weight you can hang on the trapeze, how much downhaul, and how much main sheet and forestay tension you put on the mast.