standing rigging diameter?

[county]

Hi Brion,
Thanks for the reply!

Sorry, the shroud load 12,000# was mislabeled as RM.

I am using the graph in The Riggers Apprentice from Skene's Elements of Yacht Design (Foot-Pounds/D.W.L in FT.)

33' L.W.L RM=45,000
beam=11.17’

(RM*1.5)/(1/2*beam)
=(45,000*1.5)/(1/2*11.17’)
=67,500/5.58
=12,097#

Am I doing this calculation correctly?

How do I calculate what % of the load is divided among the shrouds?

How do I find a reliable source to determine load-bearing of 1/19 (the websites I looked at have varying loads)?

What I refer to as "intermediate backs" are shrouds led from the mast hound where the inner forestay connects to the same chainplate as the aft lower shrouds, connecting aft of the lower shrouds. I will refer to them as aft intermediate shrouds. My boat was designed with aft intermediate shrouds. I would like to avoid the added complexity of running backstays. Why do you think runners make more sense for my boat? I believe many cutter-rigged boats have gone below the Great Capes without them.

Thanks for your input. It is really appreciated,
Karl

[Brion Toss]

Hello again,
First, the data I have for your boat shows a waterline of 32ft. Even at 33ft, you would probably be well shy of 45,000lbs rm at 30 degrees. A direct incline test could confirm this, and I recommend one. Meanwhile, 5/16" uppers and 9/32" lowers look right. For more details, see the "Rigger's Apprentice," or be in touch with the shop to set up a consultation.
As far as runners go, as I said before, those aft-led intermediates are not making a useful contribution, and runners will. It would not be adding needless complexity, but restoring needed complexity. And there are ways to make them very simple to use.
True, many cutter-rigged boats have sailed below the Capes without them, but hey, some of those boats didn't have standing backstays either. Your intermediates were a misguided attempt, long-since abandoned by people like Bob Perry, to get rid of runners. The attempt resulted in poor staying, compromised pointing in storms, chafed mains'ls, and a higher incidence of unintentional jibes.
As for wire strength, there are international standards for a given diameter, construction, and alloy. Whose numbers are you looking at?
Fair leads,
Brion Toss