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If we could find a way to tension a wire up near its breaking strength to validate it and its terminals were still good you wouldn’t want to be any where near it.
While the full test load a 34’ long 3/16” cable would elongate 3.7 inches, and if it were to fail would recoil like a razor sharp rubber band slicing anything in its path. Add any deflection in the hull (think of it acting like a fiberglass bow) and the wire end would be traveling like a bullet if it failed.
I think this one of those situations where the cost of any means of non-destructive testing would exceed the replacement cost of the item being tested.
Phil Agur s/v Wing Tip Commodore, Call Sign WCW3485 IC27/270A
www.catalina27.org Vessel Doc# 1039809 -----Original Message-----
Well, Bob, the rigging tension gauges (like the LOOS gauges, for example) measure deflection under an exact load--but the load is very much reduced from what the rigging might see in a 35 kt wind, and is a mere fraction of the ultimate wire strength. The LOOS gauge is normally used to ensure that your standing rigging is tensioned at 10-15% of its breaking strength, and it does that by applying a small sideways force and measures the miniscule amount that the rigging bends under that force. This is an indirect way of measuring tension...
Considering that 3/16" SS rope is rated at breaking strengths in the 4000 lb. range (depends on the construction of the strands), it would be really hard to give our shrouds a full-scale test. (Hang a pickup truck from our forestays? It might get grease on the furled jib... ) Besides, producing that much stress on a shroud would only add to the fatigue factor--and as Phil pointed out, fatigue can't be observed visually. There was an anecdote in To Engineer Is Human about a pilot flying loops in a small plane that wasn't built to fly loops. He thought because he'd done it before and survived that he could continue to do it. Well, aluminum work-hardens, and fatigue builds up when the metal is stressed, making it more and more brittle and weak... and eventually, a wing broke off. Eventually, too, our shrouds may fail.
I have my boat on the hard in my driveway, and the mast and rigging are all in separate places about the yard and garage. I had the opportunity to do a VERY thorough rigging check, even though the surveyor had given us a clean bill. I was surprised to find two corroded inner stay fittings and one mainstay wire that had a tiny, neat wrap of electrical tape, under the end of the spreader cap. Removing the tape revealed 5 of my 19 strands of stainless were broken clean through, and half of the rest look granular and crystalline under my microscope. Also, my backstay has a nicopress sleeve installed about ten feet up from the stern fitting, and I'm guessing that there is a fracture hidden below that, as well. I'm biting the bullet and replacing all my standing rigging <sigh>.
Oh--for what it's worth on lifelines: I saw a study (should have kept a copy!) done by the Coast Guard or Navy or someone else with authority that demonstrated how poorly our lifelines protect us. It's not the 'leaning against the rail' that breaks them--it's the 200 lb. man falling across the deck and hitting them suddenly that can produce about 2000 lb. of impact force. Fortunately, I weigh only 184 pounds <grin>. And I'm making my own replacement stanchions and pushpit from 11 ga stainless (.120" thick walls), just to help out...
David Shaddock 1977 C27 #3495 Pixie, in Rockford, IL |
- RE: catalina27-talk: Shroud connections to the hull Phil Agur
