I’m curious how many of you have replaced your stainless steel chainplates. If not, why not?
We replaced the 316 austenitic ss chainplates on BCC 116 (launched in November 2000) in 2015 with plates fabricated from duplex ss (2205 for most of the plates, 2507 for the bobstay plate, the lower backstay plate and the boomkin shroud plates right near the waterline).
We used carriage bolts carved from 2507 duplex (on the basis of going one grade higher for the bolts to ensure against crevice corrosion when using any ss).
We had stress crack corrosion signs on the shroud chainplates. The carriage bolts looked okay.
2205 duplex ss is stronger than 316 austenitic. 2205 and especially 2507 are immune from chloride-induced corrosion.
I think 316 ss is a compromise: low price, but low longevity in an environment that includes warm saltwater. A duplex ss chainplate could be expected to have a longevity of 25 - 30 years or more. 316 austenitic ss is perhaps half that (but if the environment is cool and low in chloride ions, such as on the Great Lakes, it’s a different story for 316 ss).
Bronze is better, but in the small economy of Australia it was easier for me to source 2205 and 2507 duplex ss plate and have it fabricated (and for the cranse iron, the upper and lower backstay plates, and the bobstay plate, welded) than to get a local bronze foundry to make what Zygote needed.
Minor edits for accuracy and completeness and to minimise typos
Ahoy Barefootnavigator, I had similar SS chainplate failure as Bil of BCC Zygote.
I was warned in a pre-purchase survey to just replace the factory SS structural pieces every 10 years, as a general rule . After finding spiderweb type cracks eminating from clevis pin holes on both sides of the midship plates , I changed to new plates.
Research exposes that SS in prolonged contact with warm stagnant saltwater, will cause crevice corrosion in the SS . This condition has something to do with an attack of free chloride ions found in the saltwater .
The SS "T"strap toggles on my factory SS turnbuckles seem to cause trapped saltwater between the toggle cheeks and the SS chainplate thus crevice corrosion at the pin holes was the result.
IMO the corrosion I experienced in this situation could have been mitigated by using bronze toggles .
How difficult was it to remove your chain plates?
Very little problem removing chainplates, Luke.
Most problem was with the bobstay plate, which in most if not all Sam L Morse Co boats is embedded in GRP. So I removed as much as I could from the forepeak, covered what I could not, had ventilation fans and appropriate personal safety gear, and a small cutting wheel.
The cranse iron knocks off the bowsprit.
The chainplates for the bowsprit shrouds, mast shrouds, and boomkin shrouds are throughbolted to/through the hull. The nuts for the boomkin shrouds are accessible in the lazarette; those for the bowsprit shrouds (aka whisker stays for some) are accessible in the forepeak. And nuts for the mast forward shrouds are in the forepeak. The lowers and intermediate are in the cabin and then the game is to remove the minimum number of ceiling strips (if you have ceiling strips) to get to those nuts.
The upper and lower backstay plates are throughbolted together through the boomkin.
In Zygote’s case, the SLM Co boatyard had used what looked like 3M 5200 caulking. Perhaps because the caulking was not generous or because the boatyard torqued the nuts soon after installing the chainplates, the caulking layer was thin and did not present any problem for removal.
I countersunk/chamfered all bolt holes and only torqued the nuts on the second day after liberal application of caulk, but I doubt that will pose a problem for removal of the plates in future.
As always, your insights/research is tremendously helpful. I was wondering if you explored the possibility of using titanium at all.
It seems the price is coming down considerably and since it’s stronger and more corrosion resistant than stainless, we’re currently thinking about replacing the chain plates et al. with either bronze or titanium.
We changed the chainplates on Z in 2015 and in Australia (a small economy, compared to the US, that is an expensive shipping route away).
I researched titanium, but quickly found the duplex stainless steels were more easily sourced, less expensively purchased, and easier to machine.
I had of course also looked at bronze. I could not find a bronze foundry in Australia that could produce what I wanted for the right price. When we cruised Southeast Asia, I’d visited small-scale bronze foundries and watched them casting propellers and other marine parts. That quickly taught me about potential problems (and just repeats again the history of the two competitive dinghy sailors, Ron Allatt and Stan Le Nepveu, who in Australia in the 1950s showed that voids and other casting faults in bronze fittings just made bronze more suspect than 316 stainless steel. Ron and Stan are likely known to you through the brand Ronstan). The US does produce quality and reliable bronze. And I like the forgiveness of bronze - its elasticity for example - that makes it a superb fit for a BCC. The shipping cost of bronze from the US made it impractical. And one BCC owner who replaced his chainplates with bronze had had a messy experience, due perhaps to machinists who were unfamiliar with bronze (you’ll find the story on the Forum).
We found local machine shops very familiar with cutting, welding, etc duplex ss because they serviced industry sectors - handling pipes for natural gas and large scale reverse osmosis systems - using duplex ss every day. Those industrial sectors and the machine shops were competitive and had all done the financial research to prove to themselves that the higher cost of duplex ss over 316 ss (in terms of service life, cost-benefit etc) was v much in favour of duplex ss.
Of course, we were helped by a downturn (in 2015) of those industries, meaning that our chosen machine shop was quite happy to entertain our one-off project, including making tiny modifications to the shape of a couple of shroud chainplates that I think delivered better shaping - and less pre-stress caused during installation - than the original chainplates).
Laser cutting the square holes that accepted the carriage bolts was a plus - I suspect that a big part of the stress that lead to stress crack corrosion associated with the bolt holes in the original 316 ss was caused by the way the original holes had been made.
Of course, if I’d had Z built with bronze chainplates, I’d likely not be talking about this now. Regrets … I’ve had a few.
In addition, the duplex ss route for chainplates had been sailed before by others. A US cruising couple well known on the E coast of Aus - Jim and Ann Cate - had changed their chainplates (not on a BCC) to duplex ss years back. I’ve forgotten how old the Cates’s duplex ss chainplates are now, but the longevity is impressive.
For the record, I talked to Pete at Pt Townsend Foundry a couple years back, and he said they were given all the patterns when Sam L Morse closed. Bronze has many alloys and they can work with you to find the best one for the job.
Thanks Bil, that makes perfect sense.
Based on all of your research from a material perspective (strength, corrosion resistance, etc.), assuming price and material availability were not an option, which of the three would you have chosen?
Rich- Thanks for the tip on PTF. I’ve reached out to them on other things and while I’m sure they do great work, their lack of responsiveness doesn’t really give me a lot of faith that I’d get the chain plates and other fittings when I need them. I waited a month before getting a response back on a replacement handle for our manual anchor windlass. I only got a reply after I sent another email to follow up. We’ll see how long it takes before I actually get the new handle.
Based on all of your research from a material
perspective (strength, corrosion resistance,
etc.), assuming price and material availability
were not an option, which of the three would you
Excellent question, Mike.
I think I would have tossed up (a) bronze and (b) duplex stainless steel.
And I’m not certain which one would have got the nod.
Let me go back a step in the process … one of my aunts married a metallurgist. He spent much of his life in academia but also was a consultant to industry.
When I discussed the problem with him, he suggested I consider duplex ss. His argument was that in addition to being relatively resistant to stress crack corrosion, oxygen starvation corrosion, and attack from chloride ions, duplex ss is stronger than 316 ss. So I could preserve the same scantling, the same dimensions of ss, and get greater SWL on top of the anti-corrosion benefits. Plus the shiny look of ss (which attracts people who do not understand bronze patina, meaning the production boat buyers who think that shiny 316 ss is boat jewelry instead of a liability of stress cracking without a warning).
When I raised bronze with my metallurgist uncle-in-law, he said he’d need to run the numbers and suggested that he’d prefer making the shroud chainplates a little thicker in bronze than the dimension used in the original ss plates.
I quite like bronze and think that the tiny bit of elasticity in bronze is quite valuable - in the sense that in a sudden stress event, the bronze chainplates can stretch a little instead of requiring the wire rope to deal with all the transient stress.
I looked at ordering the bronze chainplate from Port Townsend Foundry. (Side note: I’d commissioned the construction of Zygote by Sam L Morse Co and accepted the standard spec of 316 ss chainplates. I now think I should have dug further into my savings and opted for bronze.) When I looked at the specs of the chainplates of PTF bronze, I rightly or wrongly thought that the PTF shroud chainplates were thicker than Zygote’s original 316 plates (and that would fit precisely with what my uncle was saying about the scantling issue). If so, that would mean I’d have to have larger rigging toggles to accommodate the thicker plates.
For the tl;dr short version:
If you are upgrading from 316 ss chainplates, check out the thickness dimension (and even the bolt spacing and bolt hole locations) of the PTF bronze chainplates. If I was building from new, I’d go happily with the PTF bronze.
I was upgrading from 316 ss, so I chose duplex ss (2507 for the wet area plates - meaning the bobstay plate and the transom plates; 2205 for the cranse iron and other chainplates; and 2507 for the carriage bolts on the principle that ss bolts should be a grade stronger and more corrosion resistant than plates because bolts are starved of oxgyen).
Roger Olson’s chainplate diagrams in the BCC Construction Manual were good for plate cutting (except for the bobstay fitting diagram, which is a tad weird; and the backstay fittings on top and bottom of the boomkin, the bolt holes of which did not correspond perfectly with the holes in the original plates).
And a late note:
If I were doing the chainplate replacement project all over again (and had the luxury of time and preparation), there is one extra thing I just might do …
Douglas, the owner of BCC Calliste, came up with the idea if I am not mistaken: why not choose one chainplate, say the chainplate for the cap shroud, and make it longer so it runs below the waterline. No need for additional bolts, just curve the plate to suit the hull.
The rationale being that you then have a lightning ground on the exterior of the boat. You can even make the connection electrically better by running a copper cable from the masthead, parallel to and along the cap shroud, all the way to the chainplate.
Thanks Bil! Great thoughtful and detailed information as always.
We’ve got a little while until we get to this project, but I want to start thinking about it now and doing the appropriate research in order to make the best decision (and have the parts ready) when we execute.
I had not thought about the lower modulus of elasticity of bronze as an advantage before, but I really like the point you raise about the chain plates sharing the stress rather than relying on all of the other components.
I’m also still looking closely at the entire standing rigging system…I know the fittings/method is pretty standard among all boats, but when I look from chain plate to shroud all I see is a wide range of components and each of them is a potential source of failure. In short- my goal is to make the rig bullet proof. I think the geometry of the BCC rig goes a long way to getting there, but I think we can get better with respect to individual components. I’m just not quite sure how yet.
Mike, Yes, PTF might be a little slow lately, they are “movie” stars these days with all the castings they are doing for Leo
I appreciate your questions as I’m refitting Vixen and have been reaching out to those who know things and have been fortunate to find Craig who built Vixen and designed the BCC’s gaff rig. I asked him about her oversized shrouds (9/32") and he said that that is what is called for by Lyle Hess. I live in an old lumber town so I talked to our local riggers and they liked the idea because I’m calling for 316 Stainless, which is more corrosion resistant but lower strength than 304 Stainless. The other concern is that they source their stainless wire from Korea. Yes, they can order American wire for twice the cost and they say there isn’t much of a difference. They do on site testing, so I’m thinking of going with their suggestion as 9/32 is a good 30% more expensive than 1/4 inch.
I really love the idea of longer chainplates for lightening protection. Up until now I have just attached a couple wires from the shrouds to the water if it looks like lightening is forecast. Otherwise my guess at the likely path would be down the forestay to the bobstay and thus to the bobstay fitting just touching the water. That can’t be good, Thank you