split backstay tensioning

Hi

Can anybody tell me the answer to two questions.

1 How do you measure and set the tension in a split backstay. I know the tension in the backstay should be 15% - 20% of the wires breaking strength. But at the position where the single backstay splits into two bridle legs, it is about 12 feet up and I can't reach to get the tension gauge on. If I placed the correct tension gauge on the smaller wires of the split backstay, would the readings I require be half of the single wire 12 feet up?

2 The rig is mast head with single swept back spreaders. The lower shrouds are tensioned to 10%, and the cap shrouds are tensioned to 15%. The forestay has got a roller reefing system. There is a slight bend in the mast athwart ships between the spreaders and the mast head. the middle of the bow is over to the port side ever so slightly ( top of the mast over to stbd slightly). With all the shrouds tensioned equally, do I need to tension the split backstays to different settings.

Can someone advise me please.

Thanks

[Brion Toss]

Hello,
Regarding your first question, in order to get an accurate idea of what the tension on the backstay pendant is, you need to know the relative strengths of the pendant and the legs, as well as the angle that the legs form at the top. After that it's a matter of vectors, to take into account the force lost to compression.
Put another way, imagine that the legs are vertical, parallel, in line with the pendant, that each leg has a break of 5,000lbs, and that the pendant has a break of 10,000lbs. Since the combined strength of the legs is equal to the strength of the pendant, a load of 10% on each leg would result in 10% on the pendant. But the moment the legs' anchor points move apart, some of their load is siphoned off, going to compressing the deck that is between the legs. And the wider the angle, the greater the siphoning.
Calculating this is a bit more than I'd like to get into here, but you can see the fundamentals in Skene's, the Apprentice, and elsewhere.
Or you can just look at the jib luff when it is loaded, to see if the backstay is accomplishing what it is supposed to.
As for that bend, I don't think that the backstay will have much if any effect on it. It might have been "sailed-in", with the mast assymetrically tuned, then used for a while. Or it might have been that the uppers were too slack and the backstay/jibstay too tight, or everything too tight. Ever-so-slight bending, if it doesn't get worse, might be what you get.
Fair leads,
Brion Toss

Brion,

you mentioned adjusting backstay settings by observing the jib luff. I have been trying to determine the appropriate amount of backstay tension (jibstay sag) under varying conditions on several boats I sail on ie:Soling, 58' custom masthead, j105. Can you try to discribe what to look for.

thanks