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Old 20-10-2008, 13:50   #1
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are radio antenna brackets on back-stay necessary?

On examining my 45.7' spruce hollow mast, from my 1967 Cheoy Lee Offshore 40, I found what one person believes are AM radio brackets connected to each other with insulation, which in turn connect the 5/16" backstay wire almost at the top of the mast.
My concern here is the strength of these brackets, considering they are connected with 5/16" clevis pins, while the upper clevis pin connected to the mast head is 1/2" and the turnbuckle pin is 5/8" wide. Are these brackets a weak link and should they be removed while the mast is down?
The backstay is 1 x 19 wire at 5/16". This should give 12500 LBS breaking strength, but I can't find the breaking shear strength of the 5/16" clevis pins holding these brackets to the wire. One person told me too that the 90 degree angle in the brackets should also be a concern. I've included two photos of these brackets and the back-stay below. The back-stay in the 2nd photo sits on top.
any help much appreciated
dancamp009
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Old 21-10-2008, 07:30   #2
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The fitting appears to be an old style antenna insulator. If the clevis pins are 5/16" 316 stainless and are not cracked or damaged the working load limit would be about 7,200 lbs. By comparison, 5/16" 1 x 19 wire of 316 has a working load limit of only 2,200 lbs and a breaking load limit of 11,000 lbs. (See Suncor Stainless Inc. ).

In theory, if every thing is intact without any cracks or elongation in the pin-holes, and the wire is not too old, you are probably okay. If the mast is down, however, and one can judge the age of the rigging from the fitting, I would replace it, and likely the other standing rigging if it were my yacht. The materials are simply too inexpensive to take a chance with and there is no sense being penny wise and pound foolish.

FWIW...

s/v HyLyte
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Old 22-10-2008, 10:33   #3
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Thank you so much svHyLyte
I do appreciate your technical advice and your personal opinion. I will now go right down and price replacing these wires today with 3/8" wire just to be safe considering someday I would like to cruise the south Pacific and my chainplates have been replaced (don't know when) and look good (2" wide x 3/8" thick SS with monel 3/8" bolts}. Hope you are right on "inexpensive". But I guess that is all relative to my own pocketbook and how much I value my life.
thanks again,
happy cruising
dancamp009
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Old 22-10-2008, 10:53   #4
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Quote:
Originally Posted by dancamp009 View Post
.... I will now go right down and price replacing these wires today with 3/8" wire just to be safe considering someday I would like to cruise the south Pacific and my chainplates have been replaced (don't know when) and look good (2" wide x 3/8" thick SS with monel 3/8" bolts}.....
Going up in size on the standing rigging is not generally a good thing. It adds weight to the rig just where you don't want it. This affects the sailing qualities of the boat as well as the righting angle. If the rig was truly under-engineered to begin with, then you should probably get some help from a qualified rigger to asses what changes to make. Most likely the rig was reasonably engineered and you can stay with the same sizes, just new replacements and complete inspections of what is left.

Paul L
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Old 22-10-2008, 12:22   #5
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Aloha Dancamp,
I know nearly everyone is tempted to go with the next size larger in rigging when replacing it but it is really totally unnecessary and I agree with what Paul said above. Just replace with the same size you have unless original specs call for 3/8. If you are not using your backstay for an antenna then you don't need the insulators.
Kind regards,
JohnL
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