shroud tension for oversize wire

[asdf777]

I just learned that the original wire size on my boat is one size smaller than what is there now. It's Bristol 29.9, keel stepped sloop.

Original: 7/32" forestay, backstay and upper shrouds. 3/16" lower shrouds.
Now: SS 316 1x19 1/4" forestay, backstay. 7/32: upper and lower shrouds.

Any advice on what to do with the shroud tension? Is there anything else to worry about? The lower shrouds are sagging in waves unless they're tensioned 15% of their breaking strength.



Thanks,
Gleb

[Brion Toss]

Hi,
Too many anomalies here. Oversized wire should be tuned less, relative to break strength, not more. Remember, tuning is about dealing with elasticity. Also, note that there is no guarantee that the original rig was the correct size. What is the vessel's maximum righting moment? Next, "sagging in waves" is a less-than-precise description of the behavior of the wires. Finally, there are other reasons that you might be seeing slack rigging, even with high tune. None of those reasons are pleasant. I'd look first at the mast step/compression post/deck components.
Fair leads,
Brion Toss

[asdf777]

Hi,

Official displacement is 8600 lbs. When loaded, probably 9600 lbs. Balast is 3600 lbs. Capsize ratio - 1.92.

Not sure about righting moment. Is there a way to calculate it? I've never done an incline test. Can I perform it without special equipment?

What I meant to say about "sagging in waves" is that unless the tension on the lower shrouds is less than 750 lbs or so (or maybe 700 lbs), those lower shrouds on the leeward side will momentarily sag/loosen/slacken after the boat goes down the wave and hits the trough. They swing freely for a moment, thus when going back to tension, there is probably a high/shock load on the chainplates and through mast bolts.

Given that the original wire size is 3/16", I'm worried that 15% of the breaking strength of 7/32" wire is ~25% of the 3/16 breaking strength, which is a high load for the 35 year old through mast bolt holding the double tang. Or maybe not? What do you think?



Hopefully it makes sense,
Gleb