Why should uppers be thinner than lowers?

[cmm]

I wish there were more evangelistic operators in the yachting industry - I'd love my engine installer to become evangelistic about using stainless fasteners in my bilge.
Thanks, I fully take your point, Brion, and re-reading your earlier post "the lowers should be sharing less than half the total load", I interpret that to mean a pair of fore and aft lowers working together share less than 50% of the total load on one side of the boat, and so each lower carries less than 25% of the load (and therefore need not be as strong as the 3/8" upper shroud).

Although it hasn't been said in the thread, I presume Matt's Valiant has Upper and Intermediate shrouds, and that the "total load" referred to by Brion is the sum of the Upper, Intermediate and Lower loads.

Martin

[Brion Toss]

Hi again,
And oops, I mispoke. The lowers share about 55% of the total transverse load in this rig, so each of them takes less than half of that load. Because the load moves around some, due to things like reefing and dynamic motion, it is prudent to make them a bit stronger than 22.5% of the total, but each wire will still bear significantly less than the upper, so can be smaller.
In our example, if the uppers are 3/8" at 17500lbs, and that is something like 45% of the load (the upper's share), then 55% would be on the order of 21000lbs. Half of this is in the neighborhood of the strength of 5/16".
Is that clearer? Thank you for bearing with me.
Fair leads,
Brion Toss