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Old 06-04-2013, 12:19   #1
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I have a 43 foot sailboat ketch rig that has a split backs stay. The Rigging Books suggests that I load the rigging wire to 15% of the working load But would you do this with the split back stay. It seems like that would put too much of a load on the forestay. Any Riggers out there
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Old 06-04-2013, 15:18   #2
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Re: Split back stay

Wow! That's quite a technical question and it depends on a lot of factors. I'd consult a professional rigger and I think we have a couple here on the forum. Hopefully they'll respond.

Are you talking 15% of the working load for one backstay or two? Are you talking smaller wire for your backstays than your forestay?

I won't even pretend to know the answer at this point and just want to keep this question alive to get others to respond.

kind regards,
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Old 06-04-2013, 16:12   #3
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Re: Split back stay

I have a 43 foot sailboat ketch rig that has a 2 backs stays. The Rigging Books suggests that I load the rigging wire to 15% of the working load but would you do this with the 2 back stays. It seems like that would put too much of a load on the forestay. Maybe the loading of the two 5/16 equals the loading of the 3/8 forestay.
The forestay is 3/8 and the back stays are 5/16 Any Riggers out there
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Old 06-04-2013, 17:30   #4
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Pretensioning the stays to 15% is rather a generalization. Especially since cruisers commonly replace the wire with one vastly oversized. One should tension only enough to "get the job done". If you have heavy furled headsails then enough tension to keep them from banging around at anchor could be a guide. If the headstay seems to have too much sag on a beat then more might be good. Some boats tension for a certain bend in the mast. Some until the door to the head cannot be closed or the planks groan.

That said, given a split stay you would put half the load in each stay.
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Old 06-04-2013, 17:31   #5
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Re: Split back stay

Split backstays, aren't they for trimming while racing to help control sail shape of the main?
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Old 06-04-2013, 18:12   #6
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Re: Split back stay

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Originally Posted by daddle View Post
That said, given a split stay you would put half the load in each stay.
Breaking strength of 3/8 = 17,500
Breaking strength of 5/16 = 12,500
15% of 17,500 = 2,625
15% of 12,500 = 1,875 times two = 3750
This equates to 21% of the 3/8 forestay

I guess that is why it was designed that way to accommodate for the load of the roller furling?
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Old 06-04-2013, 18:24   #7
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Re: Split back stay

I see what you are saying. Split backstays usually mean they attach on both sides aft of the cockpit somewhere. If yours meet somewhere up the backstay and are not dual then take 15% of the wire diameter of the single that goes to the top of the mast. Then tune as daddle has said.

Any real riggers out there?
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Old 06-04-2013, 18:51   #8
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Re: Split back stay

The way I was taught:

Adjust the forestay/headstay to get the desired mast rake.

Begin tensioning both the headstay and the backstays, maintaining rake.

Stop when headstay is at the desired tension (15% is pretty typical, but some may go as high as mid-20s).

Split backstay tension will be whatever it is. The goal is to maintain the desired headstay tension and mast rake. Because the angles on the backstay are different from those on the headstay the tensions won't be the same, so you can't really say 15% all the way around. Also consider whether or not your spreaders are swept back. If they are your shrouds will also contribute to headstay tension.

If your backstay is split all the way to the mast head you have redundancy in case of failure. You can also rig a couple of blocks and a tackle as an inexpensive backstay adjuster so you can play with tension, mast bend, etc. while sailing.

Typical settings:

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Old 06-04-2013, 19:26   #9
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A bit misguided to use a percentage of breaking strength for a rig tune guide. Who chose the wire size?

Above, the calculation gave a total tension of 3750 pounds-force. That is a huge static tension for that size boat. I doubt my hydraulic adjusted backstay goes that high. And this is likely a bigger rig.

Truly: "Enough to get the job done and no more." That's all you need to know. If bending your boat and having violin tight wires is the "the job" then by all means crank it down. At rest I adjust mine so the lower toggle on the forestay stops rattling under the load of the furled genoa: about 500 pounds-force on the gauge. Sailing just enough to give a nice headsail shape. Normal maximum about 2000 pounds-force.
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Old 07-04-2013, 04:07   #10
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Re: Split back stay

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Originally Posted by Dsanduril View Post
You can also rig a couple of blocks and a tackle as an inexpensive backstay adjuster so you can play with tension, mast bend, etc. while sailing.
That is a very cool idea...thanks
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