Tightening leeward shrouds while sailing - SailNet Community

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  #1  
Old 01-03-2009
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Tightening leeward shrouds while sailing

The latest Boat U.S. magazine, on page 35, talks about Tartan's memo in response to the near sinking of a Tartan 3700, possibly when the hull cracked under a rigging load. They said, "...if an owner tightens rigging while it is under load, he can exert enough compression loading at the mast step to cause damage."

I have a copy of Don Kohlman's recommendations on rig tuning where he suggests sailing on the wind in 15-18 kts apparent and tightening the leeward turnbuckles, tacking several times, tightening and looking aloft until the tip doesn't sag to leeward. Now, I trust Don's recommendations, and the PSC is a sturdy boat, and that's how I've been tuning mine. The leeward shrouds will have slack in winds above about 15 kts, but not in winds below that.

Clearly, this is tightening the rig under load, but you have to tighten it somehow, and tightening the leeward side while sailing allows you to turn the screws without stressing the threads of the fitting.

Any thoughts?

Dave Pomerantz, 1987 PSC 34
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Old 01-03-2009
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Hi Dave,

The method you describe is certainly the only way to do it without galling up the turnbuckles. Not just Don, but many other experts, including Toss, advocate the same (tightening the leeward turnbuckles). I think something by way of further description in the article about the Tartan must be missing.

Personally, I like to just feel, but not see, a slight easing in the tension on the leeward side in the gusts when sailing in 15 or so knots average, feel being the operative word. Tuning is way subjective. I then check with a Loos gauge back at the dock to make sure I'm within limits.

Dave Mancini
PSC34 #305 Swan
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Old 01-03-2009
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Check Alex's (Giulietta's) rig-tuning article here: Adjusting Your Rig
Also Ivar Dedekam's Sail and Rig Tuning. The procedure of tightening the leeward shrouds while under way is pretty standard.

As for stressing or galling the threads: Yes, this can be a problem, but not if you keep them well-lubricated. I use a lanolin-based product available from West Marine. Kinda smelly when you're first putting it on , but it lasted all season for us, last season.

Consider: There's got to be a way to adjust turnbuckles w/o taking all the load off them. What about the fore- and back-stays? What about when you want to un-step the mast?

We have a backstay adjuster that basically works like a big ol' turnbuckle. That thing gets adjusted while we're going to weather. It got galled (turned out it had obviously happened before we owned the boat), but I was told by the machinist that machined the replacement stainless "nut" that, as long as we kept it lubed, it would be no problem.

Jim
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Old 01-03-2009
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I don't know, Dave. I once made the mistake of lossening a turnbuckle the wrong way, and it parted like a rifle shot. No damage to the lightly built J/boat it was attached to, though.

I can't see that it should be POSSIBLE to tighten shrouds enough to damage the hull, I would expect the shroud or the turnbuckle to fail--by design--before the hull could be damaged by it.

Then again the name "BendyTeau" comes to mind.<G> But that's from the stays, not the shrouds. The engineers and the jury will figure out the truth behind the Tartan story. When you are dealing with retail goods and retail customers of any kind, there's no telling WHAT they're going to do with your product. considering the number of mars missions that have failed--and the credentials of the folks who have engineered them--I wouldn't be surprised if a sailboat had an engineering failure.

Or, if a customer overtightened something until something broke. Just a tad unfortunate if that was the HULL.
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My reading of the BUS article was that Tartan initially had attributed the failure to the shroud tightening as a conibutory factor but then later said it was due to a poor overlap in layup with no mention of the shroud adjustments. Did anyone else read it this way?
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Is that article online or only in print?
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Old 01-04-2009
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Jim,

What does "galled" mean?

Regards


Quote:
Originally Posted by SEMIJim View Post

... We have a backstay adjuster that basically works like a big ol' turnbuckle. That thing gets adjusted while we're going to weather. It got galled (turned out it had obviously happened before we owned the boat), but I was told by the machinist that machined the replacement stainless "nut" that, as long as we kept it lubed, it would be no problem.

Jim
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Quote:
Originally Posted by camaraderie View Post
My reading of the BUS article was that Tartan initially had attributed the failure to the shroud tightening as a conibutory factor but then later said it was due to a poor overlap in layup with no mention of the shroud adjustments. Did anyone else read it this way?
You're correct. They blamed the shrouds and the layup. I was reacting more to their statements that rigs should not be tensioned under load, which seems to be an overstatement. As soon as you tighten wire beyond slack, it's under load. But they were pretty clear, I thought, about saying you should not take the slack out of the leeward shrouds which is essentially what I do.

Frankly, I'm more worried in my very solidly built PSC, about a rig failure than a hull failure. First, I don't go crazy about tightening -- I use a gauge, and second, the pamphlet that came with the gauge made a pretty good point that aggressive wave action will put more stress on a slack rig that bounces around than a taut rig that doesn't. In a stiff breeze you will have a heavily loaded rig whether you previously tightened it or not.

I did second-guess myself, however, when I saw Tartan's statement. Probably written more by their lawyers than their riggers.

Thanks for your thoughts, Dave M., I'll keep doing it the same way.

For the fellow who asked, I believe galling is when stainless screws are tightened against stainless bolts (or turnbuckles) without lubrication and little balls of metal are sheered off and weld themselves between the parts. It shouldn't happen between bronze and stainless and less so if you put lithium grease on the turnbuckles every season. Nonetheless, repeatedly tightening a stainless screw under load isn't good for it.
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HS...C2 gave a summary of the article here:
Tartan / C&C issues

It is not available on line but I have a pdf version. PM me with your e-mail if you would like a copy.
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Quote:
Originally Posted by Bene505 View Post
Jim,

What does "galled" mean?
It's damage to steel surfaces that can occur due to improper lubrication and friction. What happens is that material is stripped from one surface and deposited on the other. Stainless-on-stainless is particularly susceptible to galling, which is why it's important to keep SS parts well-lubricated.

Galling can't really be fully repaired, except by replacing the damaged parts, because it involves the removal of material from one or both.

I learned all about galling when I administered the coup de grace (it turned out) to our backstay adjuster at the end of the season-before-last . Luckily we had a friend-of-a-friend who's an accomplished machinist with access to CNC machines . (Upon the machinist disassembling the thing, it turned out I wasn't the first to abuse it, as there'd been precious few threads in the "nut" left to destroy.) The "nut" must've been of softer stainless than the screw, because the screw was fine. He didn't even have to chase it.

Jim
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