Dismasting Due To Corroded Chain Plate

[JeanneP]

This article in Latitude 38 is great, the owners of the boat have taken really good pictures. Brick House Dismasted

Have you checked your rigging very carefully lately?

[Gallivanters]

I'm certainly no expert, but...

I know the owners of Brick House and they're very meticulous about their maintenance.

Stainless Steel chain plates usually fail at the point right under the the deck... where we put so much effort to seal-out water (and can't even see them) which prevents free oxygen circulation around the stainless steel... which, of course, leads to concetrated corrosion in that spot. This is why it's prudent to replace chain plates regularly.

I replace nearly all of my chain plates every OTHER time I replace the standing rigging wires... which is about every 5 ~ 8 years OR immediately if I spot a broken strand in the wire.

Everyone talks about X-Rays as the best way to test your chain plates... and perhaps that's a fact. But a Crane Operator once told me of an acceptable method of Field Testing to determine if stainless steel has internal corrosion- aka ROT.

You suspend the item to be tested by a wire and bang it with another piece of steel and listen for it to "ring true". If it doesn't ring along the entire length - you have an internal problem... and you can hear it.

I tried this on my last boat and condimed two chain plates which had little outward sign of serious corrosion. I took them to a machine shop in order to have them duplicated... and the machinist agreed with this method of field testing.

However, I asked the machinist to punch round holes instead of squares... as circles spread the load better than squares and punching holes (instead of drilling) reduces the heat. Maybe I'm wrong but in my opinion - the only reason boat builders use squares with carrage bolts is because it makes it a one-person installation.

Afterward, while sitting (well... drinking, actually) at the Marianas Yacht Club, a group of us were all astounded at how easily the old chain plates broke once we attempted to bend them... and they both broke outward from the corners of the original square holes.

Now... would someone please tell me why all the modern boat builders have switched from BRONZE to Stainless Steel as the preferred material for chain plates? It's my understanding that maginese bronze is stronger than 316 & 304 Stainless steel AND Bronze has none of the corrosion problems induced from oxygen starvation as with Stainless Steel.

If I have my way - next time I replace my chainplates... I'll use Bronze or Titanium.

I'd prefer to use Unobtainium - but that's, like, impossible to get!

To Life!

Kirk

[redbopeep]

Hi, Kirk,

People don't like corrosion. Bronze does get green (Silicon Bronze) or tan/brown (Manganese Bronze) and well..there are those folks who like "shiny" So, they get stainless steel and are all happy about the shininess of it all even if it's not so damage tolerant as other materials.

Regular steel, once galvanized, will also last a long time in service as a chainplate and you do occasionally see that with 60's or earlier era boats built in the UK. It's certainly NOT as pretty as SS or bronze but does work well.

Our chainplates were Tobin bronze (not bronze at all but rather a brass (zinc rather than tin is used)); they were installed in 1931--they were inspected and found to be in excellent condition during a re-rigging (by a very highly respected rigger in San Francisco) of the boat 37 years later in 1968 (the year after the boat did a huge amount of Pacific ocean voyaging including the 1967 Transpac) but we replaced them in kind due to corrosion when we rebuilt the boat in 2007-2009. We think they were in decent shape until sometime in the 1980's; We actually have used sections of the 80 year old chainplates as backing plates for deck fittings here and there on the boat. So...let's see, even Tobin Bronze lasts longer than one could expect SS to last.

Cast Manganese bronze lasts a very long time. Two chainplates we did NOT replace were cast Manganese bronze chain plates added to the boat in 1939 for relocation of the running backstays. They were in excellent shape EXCEPT the holes in them were 3/4" diameter and being used with a 5/8" pin. We pressed in and then brazed in place a sleeve in those chainplates to allow the proper fit for 5/8" pin. We did replicate and have cast anew Manganese bronze bobstay iron, a few of the Manganese bronze mast collars--though others were like new, and hot-worked (bent) new forestay chainplates at the stem out of 1/2" silicone bronze plate.

Bronze is quite easy to work with compared to SS. We fabricated the chainplates ourselves--ordering the plate cut to proper width and length by the material vendor, we used the combination of bandsaw and a belt sander to round the tops and soften (radius) the edges; marking the position of the hole (for the shroud), drilling it out was easy. Here's a link to our 12/07 blog post about our chainplate project.

Yes, bronze really does last. No, stainless steel doesn't necessarily last very long in service as chainplates. I agree with your regular schedule of replacing rigging and chainplates. Better safe than sorry! If you have the opportunity to use bronze in the future, do so!

Fair winds,

[Gallivanters]

I'm with you, Brenda.

Chainplates do extend an inch or two above the deck and are all but covered by a bronze toggle and virtually out of sight from everyone... except from the owner. And - granted - bronze does tend to look somewhat ugly when it gets a jacket of green peeking out from between the toggle legs, BUT...

It still looks a far cry better than a dis-masted yacht seeking port and / or a new rig!

Well done with getting a supplier to deliver bronze straps cut to your specifications. How was the cost comparison? Do you have contact info for them? I'd much prefer to have bronze chain plates to install next time as I'd rather look past the un-sightlyness of dull looking hardware than worry about the constant dangers of rig failure due to the shortcomings of a shiney stainless steel chainplate.

To life!

Kirk

[redbopeep]

Originally Posted by Gallivanters

Well done with getting a supplier to deliver bronze straps cut to your specifications. How was the cost comparison? Do you have contact info for them? I'd much prefer to have bronze chain plates to install next time as I'd rather look past the un-sightlyness of dull looking hardware than worry about the constant dangers of rig failure due to the shortcomings of a shiney stainless steel chainplate.

Cost-- most people would use Silicon Bronze and that is a bit more costly than Stainless Steel would be (may 2x-3x or more the price of a good SS). Tobin Bronze, because it is a brass (alloy Admiralty Brass or Naval Brass), is actually cheaper than Silicon Bronze (price similar to SS); we almost went to Silicon Bronze with our chain plates knowing it would last much longer than the Tobin Bronze...Then I though "what, am I nuts--these chainplates were in excellent shape 37 years after installation and not replaced for 76 years and I'm thinking they didn't last long enough?" so we went ahead with the Tobin Bronze. We did use Silicon Bronze for the heavy forestay chainplates, as mentioned.

If not in the USA or another 1st world country where you can get the materials cert/spec sheet with your material order, I would NOT use Tobin Bronze or Silicon Bronze since there are too many brasses that one could hood-wink you with and you'd never know you weren't getting what you wanted.

Via phone (with all vendors). we ordered high quality materials from a variety of places:

http://www.alaskancopper.com/

They did the chainplates, numerous silicon bronze rod stock (1/2" through 1" cut in 6 or 8 ft lengths mostly) for our keel bolts, a 2-1/2" diameter 12 ft long bronze rod that was used for our rudder stock. They also sold us a 6 ft section of lovely (and huge) 6-1/4" diameter bronze tubing that we cut into the new spigots for our portholes.

We also ordered high quality materials from:

http://www.farmerscopper.com/

They did a 1/2" thick Silicon Bronze sheet that we used for the forestay chainplates, also numerous copper rod stock (1/4"-3/8") used for large copper rivets hand peened in the rudder as well as rig (remember we've got old-fashioned spars and rigging)

They were much more responsive than Alaskan with quick turn around on custom cuts.

Another source that we never actually ordered from was: http://sequoia-brass-copper.com/

We used a local foundry to cast all the Manganese Bronze stuff. We made all our own patterns.

Nontraditional sources: We did also purchase some large sizes of 3/8" thick Silicon Bronze Plate (used on the bottom of the wood keel as a skid plate) and 1/4" thick Copper Nickel Plate (for making block strapping) from a local, reputable, metal salvage company. If you have access to such a salvage yard (remember "reputable" is very important) you may have access to excellent quality materials at very low cost. In our case, the particular salvage yard gets well-documented leftovers from a shipyard that does many US Navy projects (thus the copper nickel which is actually submarine plate...) When we started our project in 2007, I went to the salvage yard, gave them my card and told them to call me if they got any of a certain list of materials. Over a 3 year period, they called me many times and we obtained great stuff from them at great prices.

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We also purchased red brass tubing (for a traditional shaft log), as well as 5/16" phos bronze rod (for running through/cleaning our engine heat exchanger) from:

http://www.onlinemetals.com/

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Hope that's helpful info

[Gallivanters]

Yes - Thanks!