ACMO rigging - unusual failure
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We keep our 1992 SN "Sangaris" at the dock in front of our condo in Delray Beach, FL, where she's been in her slip for two years, what with Covid and other issues preventing active cruising. Today, Katherine and I were walking to the boat at mid-day to continue readying her for our planned summer cruising (finally!).
Incredibly, as we walked up to the boat along the dock we heard an explosive "bang" and actually saw the starboard mizzen backstay break at the top of the lower swage and proceed to whip across the deck. An amazing coincidence. We went aboard and easily contained it, but what a shock. The rigging was new in 2010. Had we not actually seen it break we would have been totally at a loss to understand what had happened. Clearly, just sitting at the dock with gentle rocking had been weakening that stay. We had, indeed, observed a concerning amount of rust just above the lower swaged fittings (mostly on the mizzen stays) but dismissed it as inconsequential. That being said, in 2009 the aft lower mizzen stay blew up under load at the lower swage while we were power reaching at 8+ kts with four sails off Catania, Italy, and that is what motivated us to replace all the rigging in 2010. ACOM provided the new rigging for about $5000 US and we installed it ourselves. Our plan now is to replace all the rigging and use mechanical fittings, rather than swages. But to have a stay "blow up" at the dock while you are walking by seems pretty bizarre - good thing we were not on passage. All experiential input from fellow owners, of course, would be appreciated. Cheers, Craig SN68 Sangaris, Tropic Isle Harbor, FL
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Bill Kinney
Craig,
Speculating on a topic like this without actually inspecting the materials is likely to be a problematic exercise, but I have an idea for you. Note well that I am discussing this having MUCH more experience with SM rigs than SN, but I do not believe that Amel made significant changes in the way they designed these systems. I think your mizzen backstays are (much) too tight. Your description of the failure you were lucky (???) enough to have watched as involving an "explosive bang" is a pretty big clue. At rest, these wires should not be that tight. There are a LOT of moving parts here. The length of the triatic, and the degree of rake of the masts are key. You say your rig was made by ACMO, so it's a reasonable assumption that the triatic was the right length, but you might want to confirm that. Did you measure the tension in the mizzen backstays during the rigging process? If not measured, would you describe them as "ringing" tight? Did you need to tension them significantly to pull the mizzen back to vertical after making the adjustments to the main mast? Did you measure the mainmast backstay tension? I am wondering if the mizzen backstays and triatic are taking more than their fair share of the load of the forestay tension. The fact you have had TWO failures here seems to indicate something is systemically wrong... I hesitate to blame the swages, all the ones I have seen from ACMO where very high quality rotary hammer swages. Can you post a photo of the failed parts? Bill Kinney SM160, Harmonie Hollywood, FL, USA.
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Hi Bill,
Many thanks for your thoughtful and experienced reply plus your sage observation about speculating from afar - that's always an issue with this DB, but the idea flow is super, regardless. I did an autopsy on the failed swage today - the first picture shows the inside of the swage with the outside strands having broken right at the top and the core strands breaking maybe an 1/8" down into the swage. The second picture, where I've cut the swage open, seems to show that the cable further down in the swage looks perfectly ok. I think the brown-ish surface stain down deep is just the grease they apply during the swaging process.   Below is a picture of one of the other stays which is showing pretty much the same rust as the backstay that broke. The picture on the right is of the end of the broken stay. It shows that all the outer strands broke at about the same level and the core strands are a little longer, that is, they broke a few mm's into the swage. (The perspective make it difficult to see that they stick out a bit, but they do.)   -- I have been in touch with ACMO and they said that, while ss does not normally rust, it is important to thoroughly wash the wire above the swages with soap and water when they are new to remove the swaging grease that may migrate out of the swage and form a dirt trap that can cause rusting. The actual reply, which may lose a bit with the "Franglish" was, " It is important to know that this is not necessarily rust, the parts are in stainless steel and cannot rust except for concerns of contamination with an external element. Did you try to clean with soap and water? But if it's broke, it's broke. For the futur : The first months, it is important to clean the cables with soap and water because grease can come out and "stick" the dust, which gives this rusty color.
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Bill Kinney
Craig,
Your description of the amount of tension on your backstays sounds perfect... so much for my theory... The construction of the swage certainly looks good mechanically. The photo is not detailed enough, but the broken ends of the wire, either in the swage, or at the end of the cable... they look quite rusty and brown. A sudden catastrophic failure from work hardening would leave the ends of the wire that came apart bright and shiny, but grainy looking. What I THINK I see is evidence of slow stress corrosion cracking of the inner strands of the wire. We had a failure of that type on one of our jib cars. The photos there might give you an idea what I am trying to describe... https://fetchinketch.net/2019/07/26/failure-analysis/ I'm a bit surprised at the comment that stainless steel "can not rust." That certainly isn't my experience either in industrial or nautical situations. On our old ACMO rig we would polish off the surface rust off the swages and lower foot or two of wire every six months or so, and it would come back. More slowly if we waxed it, but still inevitably. I doubt the swages were still oozing assembly grease a decade after they were made. Bill Kinney SM160, Harmonie Hollywood, FL, USA
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What a wonderful forum. The expertise and experience here is astonishing. I do take issue with the comment “stainless steel doesn’t rust” although I suspect something may have got lost in the Franglish translation. I suspect that over the years we’ve all left a knife or something not well built in a wet stainless steel sink for a few days and have come back to see rust stains on the sink as much as the knife. Luckily a bit of a polishing seems to resolve the issue and keep our marriages intact.
Stainless Steel depends on OXYGEN not to rust. When it gets exposed to oxygen, the chromium and nickel form an oxide coating film that occur to cover up even minor scratches preventing rusting. It’s that shiny oxide layer that gives it its “rust free “ appearance. Stainless steel certainly can rust when deprived of oxygen and when exposed to “halide” agents that can break down the oxide layer such as fluorine, iodine and CLORINE. Guess what salt is made of... NaCl (Sodium Chloride). So left in grease, in a salt water environment deep into the swage where there isn’t a lot of oxygen... it’ll rust... eventually. Scary how you didn’t really have much warning of the impending failure. Delos cut one open in one of their Thailand videos a few years back and most of the damage was deep down in the swage on that as well. Brent
On Apr 13, 2021, 10:44 PM -0400, Bill Kinney <cruisingconsulting@...>, wrote:
Craig, --
Brent Cameron Future Amel Owner & Amel Owner Registry Moderator Oro-Medonte, Ontario, Canada
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Ian Park
Bill,
Thank you for sharing your expertise. As a non engineer I learn so much from this group. It also 'jogged' me back to the recent discussion on plastic tube covering on stays. I remember on my previous boat, a Jeanneau 37, that it had these plastic sleeves. Every so often I would slide them up a few feet and they would always deposit an appreciable amount of dirty rusty water on a nice white deck as well as leaving the link into the swages very dirty. I cut them off and decided not use them again. I was interested in your comment that stainless steel needs oxygen to prevent rusting. I'm now guessing that the retention of water by these sleeves, especially down at the important junction with the seats may be an argument for not having them on the rigging? I will also start having a closer check on my Genoa sheet carriers!! Thank you for taking the time to give us your detailed insight. Best Wishes Ian Ocean Hobo SN96 UK (Wales)
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