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
----- Original Message -----
From: [EMAIL PROTECTED]
Date: Thursday, June 15, 2006 20:58
Subject: Re: catalina27-talk: Shroud connections to the hull
To: [email protected]
> Here's my question: Are sailboats designed to withstand certain
> levels of
> wind or shroud strength?
>
> If so, they all one needs to do is create those loads -
> statically or
> dynamically, to be assured that your boat is "safe" or
> not. We have shroud tension
> gages. Why not use one, while placing the shroud under the
> test load?
>
> - - -
>
> I recently had a survey done on my Catalina. The way that the
> surveyor
> determined that the lifelines were good was to put an impulse
> load on the
> lifelines with his body and watching the stanchion to deck
> connection. Simple, but
> effective.
>
> Bob
>
----- Original Message -----
From: [EMAIL PROTECTED]
Date: Thursday, June 15, 2006 20:58
Subject: Re: catalina27-talk: Shroud connections to the hull
To: [email protected]
> Here's my question: Are sailboats designed to withstand certain
> levels of
> wind or shroud strength?
>
> If so, they all one needs to do is create those loads -
> statically or
> dynamically, to be assured that your boat is "safe" or
> not. We have shroud tension
> gages. Why not use one, while placing the shroud under the
> test load?
>
> - - -
>
> I recently had a survey done on my Catalina. The way that the
> surveyor
> determined that the lifelines were good was to put an impulse
> load on the
> lifelines with his body and watching the stanchion to deck
> connection. Simple, but
> effective.
>
> Bob
>
