Care to speculate? ARC 22 mast

Ah, a sad day for the 22! And we were having so much fun, in some of the first real summery weather we've had here in the NW. Downwind under spin with 240 lbs of crew weight on the wire, hull flying in flat water, when BANG! The spin hlyd lets loose, causing momentary confusion. We hoist again, and I happen to look up to see the mast falling off severely to port, with the stbd upper inner diamond hanging limply. We douse the chute and limp home to assess the damage.
Upon dropping the mast, we expected to find a tang that had let go, or a turnbuckle failure. But no, all of the diamonds were intact, with no evidence of damage. The turnbuckles came apart easily, the threads on the studs were fine. The female threads in the open body, chrome plated bronze turnbuckles are a bit hard to see clearly, but they seem fine too, with no hint of stripping anywhere. The pics show the mast with the diamonds relaxed, but it looked pretty similar before we loosened them.
So we'd love to come to some understanding as to what happened. Did the hlyd release somehow stress the mast? Did something giving way induce the release? Are they unrelated? Did the mast just bend under spin load(modest as it was)? Which doesn't seem too likely as the bend is just above the upper tang of the inner diamond, not above the hounds. We're baffled at this point. And we'd like to know what went wrong to avoid such an expensive(I assume) event in the future.

Here's the fine print. This boat is the prototype ARC 22, with the original 38.5' aluminum mast. It's currently running a single spreader, double diamond set up, but was initially rigged with 3 spreaders. So there are a fair amount of filled holes. And it's 20 years old, and spent much of it's life near salt water, some corrosion. Although the bend is no where near any of these defects. All the diamond wires and turnbuckles were replaced at the beginning of last season, and again show no failures. The mast strikes me as pretty highly stressed, with the outer diamonds tensioned to induce 3.5" of prebend, and the inners tensioned considerably less, just enough to stabilze the tube between the outer diamond attachment points. All was carefully set up 6 weeks ago to Aquarius' precise specifications.

So, thoughts gentlemen?

And, it appears we're in the market for a new extrusion. Any sources other than Aquarius? Anyone know who supplies them with tubes? Or other spar mfgrs who could supply a suitable stick? The profile is 6" x 3.25", I can get the wall thickness later in the week. Any used 22 masts out there?

Thanks guys, sure wanna get her back running soon, it's prime season here in MT.

Dave

I don't know what broke or went wrong but once you identify that I would be very tempted to bend it back using a fulcrum of soft/padded material over something hard. We used to use boat covers over a picnic table and had great success straightening bent aluminum spars with 505s. Not ideal but we straightened spars bent worse than this one and I use to race one of the straightened masts in San Francisco Bay afterwards with no issues. I have done the same on other boats as well.

Sorry for the basic questions, but did you have the mast rotated all the way out while sailing with the kite? Was the main on tight enough? The bend is to the side which leads me to think the mast was not correctly aligned to the forces it was experiencing. Generally you would want the mast to be rotated all of the way out so that the stronger part of the mast (the fore and aft direction) is now working to support the side loads of the kite, main, and trapeze.

I am assuming it bent to leeward and that you were sailing on port? If so, it looks like it bend the only way it could - right in the middle of the unsupported area between the hounds and the spreaders. You are lucky it didn't break and now have a chance to fix it.

Perhaps the original sets of spreaders would have allowed the mast to take more of a side to side load.

I see that the spin tang is fixed to the mast and doesn't rotate around. Most of the spin setups allow the block at the top to rotate around the mast so the spinnaker doesn't try to un-rotate the mast. That doesn't necessarily explain the issue - but I'm thinking that maybe the mast went under some kind of whipping/twisting motion when the spin loads let go suddenly and that left the kink where it is.

Dave:

Try

https://www.dwyermast.com/contact.asp

Or

http://www.offshorespars.com/index.php/contactus/contact/

or

http://www.sparcraft.com/uk/technical_support/technical_brochures/multihulls/default.asp

Interesting. I have seen a similar failure on a P19. In that case there was a bang, I looked up and I thought I saw the mast was bent and it held for a "second" and then broke(later I figured I was seeing things). In that case the diamond wires were brand new dyform. We assumed the wire slipped in the fitting but the rigger cut them and there was no slippage. There was a small difference in the diamond wire length.

I have heard of a another case on a aluminum masted non spin Tornado where the mast bent. Also new diamond wires.

In both cases, no one determined what happened. The theory was something slipped but they could not find anything.

There was another case that was not quite the same but I have always wondered about it. I was sailing an Aluminum masted Tornado in 10-12 kts with brand new dyform diamond wires. We had a perfect port start but then boat would not go. P16's were passing us. Then there was a bang high up the mast and then the boat started sailing normally. There was no damage to the mast and no indication that anything "hung up".

In all cases it was probably the first time we really cranked down hard on new diamond wires with a pre-bent mast and something slipped. I have wondered about whether I would have broken my mast if the wind had been higher.

I know I am not offering a solution, but maybe you can find a common factor.

FYI, I use solid wire, where I can, for diamonds now.

Yeah, I wonder about bending it back, maybe building a fulcrum shaped to the extrusion profile. But I'm concerned the even with a pristine tube, this spreader/diamond arrangement is just barely sufficient, Although it is the current arrangement on ARC alum masts.

This main has the 1" alum tube as bottom batten/boom, no rotation inducer, and rotation is limited by moving the mainsheet forward on the clew plate in higher breeze. As the wind was light, the sheet was attached to the furthest aft hole, allowing full rotation. Main was in tight, and when we rehoisted we were well downwind, so the chute powered up slowly. We were sailing on stbd, and the mast bent off to port as one would expect. The spot it bent was just above the upper tang of the inner diamond, so if everything was working properly it should have been well supported. That's why we're so baffled.

Thanks Lost!

dave

Jake,
There is a bail about 12" below the spin tang, allowing the spin hlyd to rotate easily. But the idea of the mast going into some violent motion when the spin let go does seem plausible. We did see something similar(very ugly) occur early last year when one strand of the stbd shroud busted. That's when we replaced all shrouds and diamonds.

Dave

Yeah, this is puzzling. Although all the wires are fairly new, the boat's been sailed a bunch since then, occaisionally near its limits. So it's somewhat doubtful that anything was settling in now. But.... We're probably not gonna get a clear answer on this. Thanks for all the input guys!

Dave

Dave

I know when i look up at my mast under spin load, it sometimes bends in odd places

just a guess here, but perhaps there was some metal fatigue already, and slipping or dropping the halyard/sail pushed it past it's point of no return?


Was it 240 lbs on the wire, plus a skipper, or was that total crew weight?

Thanks Red, I've been on the phone much of the day.

Dave

Did you have the main traveled out and were you really going downwind or were you in more of a hot spin reach mode?

You didn't happen to release the main too quickly............ I hope....

Main was travelled out no more than 6". It was really a delightful spin reach in steady, less than 10 knots of wind, flat water, conditions this boat absolutely loves. Really not a lot of stress on the rig, relatively speaking.

Dave

Didn't release the main at all, hlyd released suddenly and I just drove down and the boat slowed easily. Re hoisted, but the boat didn't want to power up again, which is what prompted me to look up, much to my chagrin.....

I think that a pre existing weakness is pretty likely, and what triggered the failure might be hard to pin point. Brad talked to Tom Haberman today, and he speculated about a compression failure. It's a complex engineering project, a mast this tall with this small an extrusion.

I'm 160 lbs, and I'm guessing that Lacy is only about 80 lbs. Brad and Matty were on the lee hull to facilitate the hull flying fun.

My SC 17 had a bend in the mast and I was able to straighten it
quite easily. I believe it was the same extrusion just about 10' Shorter. Never had a problem with it after straightening it. Give it a go before laying out the big bucks on a new one.

Ever looked at an Aussie 18 rig?

Pure speculation: My subconscious, in a fit of rage and jealously over your armada of cool sailing toys, burst into the physical world and bent your mast. Yes Dave, sheer will did you in. I can't control it, nor can I prevent it.

Yeah, an 18 rig is some sort of magic, illusion.

I don't doubt your mental powers Karl, nor your inability to control them. Get yerself another ride and leave me alone! Boatless indeed! Last I saw there were 4 or 5 of 'em following your monster truck!

I see the bail now - question, though...It looks like your halyard goes through the bail, to the hound mounted block, and back down through the bail presumably with a stopper ball or something at the head of the kite. I think the original I20's were rigged that way but we changed to a system where we ran a short pigtail line from the upper hound to a small block that stuck out just below the bail. The halyard would go through this block on the extension and the pigtail allowed the halyard to rotate better. Food for thought, maybe, for the next setup (I doubt it had anything to do with this issue). It's possible the 20's switched to that pigtail system because the bail kept bending upward from hoist pressure...I seem to remember that happening a lot.

Yeah, this is a monster bail, I'm thinking of replacing it with line on the next mast. Your tip on the pigtail mounted blk is attractive, I'll try that. Thanks Jake!

Dave

how much pre-bend was on that mast?

3.5" of prebend, as dictated by Aquarius' precise set up directions.

Ok, here's the update. We carefully supported the mast at a variety of points equidistant from the bend, and applied ever more weight/force to a wrap of webbing at the bend. We arrived at a point where we were inducing 4" of bend in the opposite direction from the original bend, but upon releasing it, we still had 2" of bend in the original direction. Crank it up again, a little past the 4 inches, and it gave, kinking.
So plan B. Bought a used mast of the same vintage from Tom at Aquarius, and arranged (expensive) shipping from MN to MT. Tuned and stepped it Friday morning, only to discover the portside upper outer diamond disturbingly slack on port tack. Dropped it, once again carefully adjusted all diamonds according to Aquarius specs(several loos readings were significantly off), and took her out again. This time a portside lower inner was slack on port tack. A spin hlyd blk failure drove us back to the beach to drop the mast again. Did the drill again, and finally got the ride we've been waiting 5 weeks for. Will probably drop it one more time to check the readings, but the boat is back!
Anyone else have this experience of setting the mast up, but when taking it out and loading up the mast, having the diamonds take a less than perfect set? Or is this a particularly finicky mast?
This newer extrusion is in much better shape than our original mast, no corrosion, no dings and dents, no extra holes for different spreader arrangements. We're very happy now, feeling much better about our chancess of keeping this stick in column. And still a couple of months of soft water sailing yet here in the Pacific NW. Thanks to all who offered advice and consolation!

Dave

If the diamond wires are new - yes, this kind of stretching is normal. I got surprised with it on a first leg of the tybee 500 a few years ago. The boat kept getting a little slower and we were having trouble staying up with the lead boat. After about another 30 minutes, I finally noticed the windward diamond wire completely slack (sailing upwind). We stopped to tension the diamonds by eye and managed to not lose any more time.

Glad to hear your on the water again (with that cat, i know you have many others)