[pomerantz]

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

 

[pomerantz]

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.