Calculating chainplates

[Brion Toss]

Hi,
I spoke with one of the good people at Selden, and they are using an even higher righting moment number, assuming a displacement of 4,500kg. This results in 7mm uppers, which I frankly find absurd. My guess is that the assumptions behind their algorithm do not correspond well to this vessel.
With a waterline of less than 22ft, and with a relatively low SA/D, the Alberg will be less stiff than most contemporary boats. A direct incline test would confirm or deny this; I understand that you can't do that at the moment, but maybe someone with a sister ship could?
I have amended the note about lower shroud size for the next edition or the Apprentice, as repeated tests and measurements indicate that it is never necessary to have double lower shrouds that are the same diameter as uppers, at least on a single-spreader rig.
I can only hope that the numbers you are using from Gerr and L&I are for single lowers; the total load on the lower shrouds is typically somewhat higher than on the uppers -- as much as a 60/40 ratio -- but twin lowers, as on the Alberg, argue for reduced lower shroud diameter.
Again, a direct test will bear out the above, or not.
As for the chainplates, use ultimate strength, just as for all other components. And trust the tables in L&I, Skene's, or my book.
Fair leads,
Brion Toss