CAS or "Chainplate avoidance syndrome"

[Cyrus Safdari]

Originally Posted by Dockhead

I think bronze is perfectly fine for chainplates, much better than SS, but ONLY IF you can avoid unlike metal issues, which can ruin bronze. Are you planning to fix your stainless wire rope shrouds to them with electrical isolation? A bronze is not indeed impervious to corrosion.

Bronze and steel are close enough on the galvanic scale to not be an issue, not even underwater. You certainly do not need to isolate the standing rigging if you're using bronze chainplates and note that people generally go up a size when switching to bronze chainplates anyway
Bronze and SS steel are used in many fittings on boats including standing rigging turnbuckles

[dlj]

Originally Posted by Cyrus Safdari

A lot of things were indeed supposedly designed "for the life of the boat" (in reality designed for cost-effectiveness by builder) ... but nobody expected that life to be 40+ years and nobody really knew the long term properties of the materials they were using 40+ years ago either. So the fact that chainplates "were designed for the life of the boat" with a built-in safety factor doesn't really mean much. There are too many other variables that can make the life of chainplates very variable ie: the specific conditions of each particular boat (the particular quality of the SS used, how well was it polished, was there a leak peeing on the chainplate for years? etc)

Truly, the "for the life of the boat" is an illusion. The illusion is from the community.

Just to be clear, 40 years ago was only 1982. In 1982 the life expectancy, pitting corrosion mechanisms, and much more was well understood then as it is today and had been for quite a few decades prior to that.

The article you linked to was quite good, and an interesting read. But it did not really "advance our knowledge" rather it explained what things that we don't know. Everything it talked about has been known for many decades. I'm not saying anything negative about that article - it's a good read - I'm only pointing out that it was not written to "advance our knowledge", it was written to talk about current knowledge.

dj

[Cyrus Safdari]

Originally Posted by dlj

What do you suggest that owners of these boats do?

dj

I'd really like to meet the guy who somehow managed to convince the world that boating was supposed to be cheap and easy LOL


The first step is acknowledging there is a problem rather than cook-up rationalizations

[Cyrus Safdari]

Originally Posted by dlj

Truly, the "for the life of the boat" is an illusion. The illusion is from the community.

Just to be clear, 40 years ago was only 1982. In 1982 the life expectancy, pitting corrosion mechanisms, and much more was well understood

What was "understood" is pretty irrelevant, what as done is relevant; whether 1922 or 2022, pitting corrosion of ss is still a fact of life, and boatyards were still as always making stuff as cheaply as possible without long-term consideration which is why those chainplates are buried in the first place despite the full knowledge that it would only promote pitting corrosion and make it harder to address

Nuthin' changes.

The fact that the chainplate is hard to reach makes it no less necessary to inspect (in fact more)


As to what to replace a chainplate with:
Look I appreciate that people lots of expertise and stuff in metallurgy, but this board is not about advances in the bleeding edges of metallurgy. SS eventually corrodes and has to be replaced; bronze is the usual replacement for avg cruisers and *sigh* you can use Ti too but really the few hundred millivolts galvanic difference is not a good justification & that's really all we need to know.

Hey, look at that lovely anchor yonder there!

[dlj]

Originally Posted by Cyrus Safdari

What was "understood" is pretty irrelevant, what as done is relevant; whether 1922 or 2022, pitting corrosion of ss is still a fact of life, and boatyards were still as always making stuff as cheaply as possible without long-term consideration which is why those chainplates are buried in the first place despite the full knowledge that it would only promote pitting corrosion and make it harder to address

The difficulty here is that you state this as a given that it will happed to every single SS chain plate. That is not exhibited in actual experience. Most of these chain plates do not have that problem and likely never will.

Originally Posted by Cyrus Safdari

Nuthin' changes.

The fact that the chainplate is hard to reach makes it no less necessary to inspect (in fact more)

So if a boat owner has a boat with buried chain plates - you are suggesting they spend thousands of dollars to dig them out and inspect them?

Originally Posted by Cyrus Safdari

As to what to replace a chainplate with:
Look I appreciate that people lots of expertise and stuff in metallurgy, but this board is not about advances in the bleeding edges of metallurgy. SS eventually corrodes and has to be replaced; bronze is the usual replacement for avg cruisers and *sigh* you can use Ti too but really the few hundred millivolts galvanic difference is not a good justification & that's really all we need to know.

We will have to agree to disagree on this point. I believe these forums are a good place to discuss all things. Those that aren't interested in some of those things can simply ignore them. You apparently aren't interested in the metallurgy aspects of the discussion - I'd suggest you move past those posts and focus on the aspects of what you do wish to discuss.

I believe this board is for anyone to talk about any aspect of sailing and cruising. Of course one should be polite along with some of the "rules of engagement".

I'm still trying to understand your position.

Is it that every boat owner should tear their boat apart looking for potential problems? What would be the time frame that this should be done within? What are the other aspects of the when and why's? I'd be happy to talk about that if that's what you'd like to talk about.

Simply bashing boat builders that all they do is build as cheaply as possible - I don't think that is right....

Most boat builders do the best they can. There are always compromises in every boat design. Some of those compromises result in more difficult problems than others. As boat owners and users, I feel it is our responsibility to talk about problems that arise and what the best solutions are to those problems. I feel that between boat owners and designers there needs to be an active and constructive dialog...

dj

[Jdege]

Originally Posted by dlj

So if a boat owner has a boat with buried chain plates - you are suggesting they spend thousands of dollars to dig them out and inspect them?

I don't know about him, but I'd certainly suggest that if you don't know when it was last inspected, that you inspect them.

And I'd suggest that you do the same for every other critical system.

And if you have any critical systems that would require thousands of dollars to inspect, that you consider that an issue to be fixed.

[dlj]

Originally Posted by Jdege

I don't know about him, but I'd certainly suggest that if you don't know when it was last inspected, that you inspect them.

In what time frame? 1 year? 5 years? 10 years? 20 years? 40 years?

What time frame do you suggest they be inspected?

Let me take this one step further - you inspected your chain plates on year 1 - how many years later should you do another inspection? Do you have intermediate inspection protocols?

Originally Posted by Jdege

And I'd suggest that you do the same for every other critical system.

Most critical systems have listed inspection time frames. But I've never seen that for chain plates.

Originally Posted by Jdege

And if you have any critical systems that would require thousands of dollars to inspect, that you consider that an issue to be fixed.

100% agree!

dj

[Cyrus Safdari]

Most of these chain plates do not have that problem and likely never will.

Well however likely or not we guess & assume, again the point is you'll never know the state of your chainplates until you inspect them.

are suggesting they spend thousands of dollars to dig them out and inspect them?

Or come to terms with the fact that they'll spend a bunch more if the chainplate fails
Welcome to boat ownership This is why we learn to do things ourselves

I dont think that's right...

First we're critical of boatbuilders all the time here and everyboat model has issues, and second if you build a boat where the chainplate is not accessible and is buried then yes sorry you richly deserve criticism on that point

And if you buy a boat like that then you need to know what you've sigbed up for

This applies to anything on a boat that requires long term difficult maintenance

[dlj]

Originally Posted by Cyrus Safdari

Well however likely or not we guess & assume, again the point is you'll never know the state of your chainplates until you inspect them.



Or come to terms with the fact that they'll spend a bunch more if the chainplate fails
Welcome to boat ownership



First we're critical of boatbuilders all the time here and everyboat model has issues, and second if you build a boat where the chainplate is not accessible and is buried then yes sorry you richly deserve criticism on that point

And if you buy a boat like that then you need to know what you've sigbed up for

This applies to anything on a boat that requires long term difficult maintenance

We have no disagreement - except one point. That point is that I feel when someone complains or finds something that could or should be improved - they should do more than just complain about the issue. They should come up with what they feel is the solution.

dj

[Jdege]

Originally Posted by dlj

In what time frame? 1 year? 5 years? 10 years? 20 years? 40 years?

What time frame do you suggest they be inspected?

Everytime you replace the rigging?

[Dockhead]

Originally Posted by Cyrus Safdari

Bronze and steel are close enough on the galvanic scale to not be an issue, not even underwater.s

Originally Posted by Cyrus Safdari

. . . but really the few hundred millivolts galvanic difference is not a good justification & that's really all we need to know.. . .

Metallurgists will disagree with you entirely here.

500+ mV (0.5+ V) of galvanic potential between two metals is way too much for the marine environment.

These rules of thumbs are widely used in design:


"For harsh environments: outdoors, high humidity, and salt environments fall into this category. Typically there should be not more than 0.15 V difference in the “Anodic Index”. For example; gold – silver would have a difference of 0.15V being acceptable.

"For normal environments: storage in warehouses or non-temperature and humidity controlled environments. Typically there should not be more than 0.25 V difference in the “Anodic Index”
"For controlled environments: where the temperature and humidity controlled, 0.50 V can be tolerated. Caution should be maintained when deciding for this application as humidity and temperature do vary from regions."
https://ficientdesign.com/galvanic-c...-anodic-index/

500+mV (0.5+ V) is way too much even for away from the sea and not outdoors, much less in a marine environment.

Now that's just a rule of thumb -- there are other factors which influence the generation of galvanic corrosion, like the relative surface areas of the two incompatible parts. A more noble metal of smaller surface area can be ok attached to less noble metal of greater surface area. But that is not this case.

Yes, bronze is commonly used together with stainless, but when the bronze is heavily chromium plated, the way it's typically done for bronze rigging parts. If you do that to your bronze chainplates, then that should be ok. But the time you do this, you've spent more than Ti would have cost, no?

Bronze does not suffer from crevice corrosion, so that makes it good for being glassed in, unlike stainless, which is fundamentally unsuitable for that application.

Originally Posted by Cyrus Safdari

. . .
The fact that the chainplate is hard to reach makes it no less necessary to inspect (in fact more)

Here I agree with you 1000% .

Glassed in stainless chainplates are actually a ticking time bomb. I had one break on me under sail, and I know people who have lost their rigs due to this. This is a serious and real and not uncommon problem, and thanks to you for starting this valuable thread. If I had a boat which had these, I would replace them with a different material, next time I change the standing rigging.

[Cyrus Safdari]

FWIW readers, here's a chart of galvanic compatibility

[Dockhead]

Originally Posted by Cyrus Safdari

FWIW readers, here's a chart of galvanic compatibility

Most bronzes we use on our boats are technically leaded brass.


But in any case -- no such simplified chart is possible for different environments and different surface area proportions. This chart is not something an actual engineer would use.



Also bronzes are different and so are different stainless steels.


But I daresay that no unplated bronze is ok in direct contact with 316L stainless in the marine environment, which is one of the worst for galvanic corrosion.



Here is one actual research study showing galvanic action between bronze (a very good tin bronze with no zinc) and stainless steel in the marine environment:





https://www.researchgate.net/publica...6c15c/download


As you can see, it's a very bad combination in the marine environment.

[dlj]

Originally Posted by Dockhead

Most bronzes we use on our boats are technically leaded brass.


But in any case -- no such simplified chart is possible for different environments and different surface area proportions. This chart is not something an actual engineer would use.



Also bronzes are different and so are different stainless steels.


But I daresay that no unplated bronze is ok in direct contact with 316L stainless in the marine environment, which is one of the worst for galvanic corrosion.



Here is one actual research study showing galvanic action between bronze (a very good tin bronze with no zinc) and stainless steel in the marine environment:


Attachment 265892


https://www.researchgate.net/publica...6c15c/download


As you can see, it's a very bad combination in the marine environment.

Nice article - a bit lacking in some areas of what I call "completeness" in terms of terminology and references but otherwise a decent article.

You should read your references, however, as you bash the bronze to stainless connection. Taken directly from your reference in the conclusions:

"5. In case of the stainless steel-bronze couple, both metals present noble behavior, the intersection of the Evans curve didn’t occur on the oxidation-reduction branches, i.e. the galvanic couple isn’t created."

dj

p.s. The stainless steel used in that study was closer to a 304, not a 316.

[Cyrus Safdari]

I indeed am not a metallurgical expert but have yet to hear of a bronze-stainless turnbuckle suffering from galvanic corrosion

This chart from "The Corrosion Society" (must have some wild n crazy office parties there!)

Apparently bronze is used as an intermediary between alum and ss to mitigate their galvanic effect on each other