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Old 12-04-2014, 08:16 AM
infinitysail infinitysail is offline
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Join Date: Feb 2014
Posts: 12
Default Safe Working Load vs Minimum Breaking Strength

I am putting together a dynex dux backstay using Colligo Marine fittings.

One thing I am having trouble with is picking the right end fittings to fit hole diameters and strengths.

The backstay was originally -10 rod, and one potential Colligo fitting, CSS91BLK, has a SWL of 7500 lbs and a breaking strength of 15000 lbs. I can't find a SWL of -10 rod, only breaking strength, which is less than the fitting. Is this fitting safe to be used if the original rigging was -10 rod?

While we are on the subject of Colligo marine fittings, does anyone have a good solution for affixing the 3/4" wide colligo fitting to the mast crane with a 1/2" hole? I was thinking of having custom stainless link plates made, as I can't find a toggle that would work.

Thanks,
Frank
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  #2  
Old 12-05-2014, 08:38 AM
Brion Toss Brion Toss is offline
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Join Date: Jun 2005
Posts: 1,180
Default Details

Hello,
First, "safe working load" is not a terribly meaningful term, without specific qualification. In yacht gear, a safety factor of 2:1 is fairly standard, which is to say that the pressure to save weight, combined with the relatively mild working conditions, means we can usually get away with that. But I use 2.5:1 or more for standing rigging, and higher on crucial pieces like V1's on disco rigs, and higher still for industrial or theater applications.
Next we need to know what Colligo means by safe working load. It might be relative to yield, not disintegration, for instance.
So we need to know if that -10 was the right size. Then we can relate its strength meaningfully to the Colligo fitting.
As for adapting the Colligo fitting to your masthead, have you talked to John at Colligo? He's very helpful.
Fair leads,
Brion Toss
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  #3  
Old 12-07-2014, 07:16 AM
infinitysail infinitysail is offline
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Join Date: Feb 2014
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Default

John finally got back to me. It looks like their fittings SWL is 50% breaking strength and I can size everything to be at least as strong as the -10 rod it is replacing comparing breaking strength to breaking strength. The dux is different in that regard, but is so oversized generally, it is not a problem.

As for -10 rod for the j/40 backstay, I have never heard of anyone dismasting a j/40 and I know there have been some hard miles put on them. The sailplan is pretty small and the SA/disp is relatively conservative.

Last edited by infinitysail : 12-07-2014 at 07:24 AM.
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