Stainless Steel Chainplates (failed 50 miles offshore)

Ross · Aug 20, 2012

captnron said:
Guys,

I forgot to mention that the lower the number of ss grade, the higher the percentage of carbon steel in the mix. All stainless has some carbon steel.

304 stainless is the worst, for if the finished coating, edges, or drilled holes left compromised, just add air, moisture & stress over time and viola, you have corrosion/rust & eventual failure.

And remember, looking at the pics of the failed chainplates this rust, corrosion & failure are very self evident.

CR

As long as air is present and sea water is the only electrolyte 304 stainless steel will be fine. It is when air is excluded that problems develop. I had a 40 year old Case brand knife break just inside the handle because of stress corrosion cracking. I check barn floors for decay with a 10 pound hammer.

tommays · Aug 20, 2012

DI water (Deionized water) is killer hard on stainless and crevice corrodes even the finest welds in 316L

jhorwitzny · Aug 20, 2012

What type of stainless does Catalina use on its chainplates and does it vary by year/model. I have a 2000 MK34 and would like to know what was installed.

EmmaC · Aug 20, 2012

We had a chainplate go and demasted the boat in the Key West ship channel with a cruise ship coming in. I was out with a friend (nothing like two middle aged women on a boat) who was not a sailor. I managed to get the sails, the lines, and the guys in the boat and tied down (along with the rest of the mast and boom). I had the engine started by the time the coast guard (who was maybe 10 minutes away) arrived. Adrenaline does that for you. All the chainplates were replaced as well as the mast. It was a 1982 Hunter 33. We loved our boat, but sold it and are now shopping a new one.

MSter · Aug 20, 2012

EmmaC,
That's impressive, I can't imagine trying to do that under any conditions.
Well done Sailor. Hope the Coast Guard brought you coffee !
Mster

DJW · Aug 20, 2012

The other thing we did when we replaced the chainplates on our 42' Cascade in HI was to moved them from being inbeded in the towrail to mounted to the outside of the haul where the are completely visible We cut the old chainplates off flush with the towrail one at a time, glassed in over the top of them and used the inbeded portion left as a backing plate that we drilled threw and then used 1/2 inch 316 SS carriage bolts from Defender to mount the new chainplates.

Dennis

RobertLangdirect · Aug 20, 2012

RECESS said:
When we bought the Pearson 6 months ago I checked the chainplates visually. . . . It only cost me $25 for each chainplate to be water jetted using my good one as a template. . .

Dang! Can you share the source, NAME and Tel Number, URL if on-line, PLEASE?

Scott T-Bird · Aug 20, 2012

Bad design for SS?

Is embedding the chainplates in fiberglass common and/or is it bad design?

It seems that a more robust fitting assembly could be secured below. My shrouds are inboard so they are mounted to a deck mount chainplate above and secured with a very beefy chainplate attached to the bulkhead with 10 bolts on each side. However the backstays are secured to the hull with the strap on the inside of the hull. The outside of the hull reveals the 3 bolts that fix the plate to the hull.

In both cases, the deck mount chainplates transfer the load below with 4 bolts for each fitting. I suppose the bolts are susceptible to crevice corrosion but at least they can easily be replaced if there is any suspicion of a problem.

I don't think I would feel secure with a strap embedded in fiberglass.

mahogany · Aug 20, 2012

Don't forget all stainless steel will rust regardless of grade, stainless steel is made partly from iron, which rusts, chrome is added to create anti rusting properties, the stainless will oxidise this forms a protective skin that prevents the air getting to the steel. However, if oxygen is excluded, as is the case if a plate is tight up against another surface or a nut on a threaded bolt, rust will form, we have all seen this under washers act.

maarty · Aug 20, 2012

Interesting topic. HERITAGE is right on the money in stating:

"Once the exterior protective coat of ss is breached the corrosion occurs very fast. To breach that coat, there must be no oxygen and salt water. Keep the salt water out and you will have no problem."

Stainless steel relies upon a microscopically thin layer of chromium oxide on its surface to remain stain-less; ie, free of rust. Crevice corrosion refers to any place upon the stainless steel, or within it where moisture cannot evaporate; chromium in the SS relies upon oxygen being in contact with it to create chromium oxide.

Crevice corrosion will happen when capillary action of a surface near the SS or a crack in the SS allows water to suck into the gap between surfaces.

It is the bedding compound around the chain-plate that is guilty of letting water in and having a capillary effect at the deck.

There are several other factors to consider here:

A) bedding compound can lose contact with what it's bedding and create a gap.

B) if the space around a chain plate where it passes through the deck is too narrow the
bedding compound has less ability to freely stretch and compress. It will deteriorate.

C) Stainless steel work hardens. This means that when it flexes, is bent, twists, impacts,
and is drilled it gets harder. When it gets harder it has less flexibility. With less flex it
is more prone to micro-cracking from fatigue.

Solutions:

A) Make sure there is a generous space around the plates where they pass through the
deck; round off all corners and make sure that deck core is sealed from any water
intrusion. Also round off all corners of the chain-plate. Sharp corners fatigue the
the fastest.

B) Use premium bedding compound. Make sure it isn't past due; check the date on the
tube.

C) Use premium stainless steel.

D) Make sure that the load on the plate is dead straight into the direction of pull; if it isn't
the plate will fatigue from the side to side bending and will develop cracks into which
capillary action will pull moisture. Make sure to use toggles as well, to minimize side
loads.

E) Eliminate encapsulation of chain-plates below decks. Never have plates buried in glass,
and, or plywood surrounded in glass. Ensure plates are never permanently moist should water get below deck.

D) Don't over torque the chain-plate bolts; doing so can cause micro cracking and work
hardening.

miatapaul · Aug 20, 2012

Scott T-Bird said:
Is embedding the chainplates in fiberglass common and/or is it bad design?
...
I don't think I would feel secure with a strap embedded in fiberglass.

In my humble opinion it is a very bad design. I know Island Packet does it, and others as well. I prefer them to not only not be covered by glass, but also not by cabinetry, so you can actually keep an eye on them. I have heard of people replacing them and re-glassing them in, I would never do that, as it excludes a good source of oxygen, and will hold moisture against the SS encouraging corrosion. Many designs have the plates behind cabinets and you can't see them without removing every thing in the cabinet, and some you have to remove the cabinets.

I do like the idea of externally mounted chainplates, but that really limits sheeting angles and is not acceptable to many people.

miatapaul · Aug 20, 2012

RECESS said:
I had them done at Voigt Steel in Valdosta Ga. That is the nearest city to me. It seems when you get inland the price goes down a lot. I took them one of the good chainplates from the port side as a template. I made sure they would not drill the holes as drilling heats the SS and weakens it. They should be punched or water jet. He said he would water jet them. I had to polish the stainless when they were done. I could not see paying to have that done as it was only a little labor with my orbital polisher.

http://voigtsheetmetal.com/

If you polished it yourself, did you do anything to passivate the stainless? That would be my concern as well as getting into the jetted holes. Without proper cit will start to corrode much quicker. But I guess that will give you a chance to try out bronze. Yes once you get away from the boat yards the machine shops are much cheaper, but they are not always as experienced in what works in a salt water environment. I always wonder how to tell if I got the correct steel. I know some are magnetic and others are not, but I don't know how to really tell.

ancientmariner · Aug 20, 2012

"All hardware will fail over time,...Twenty years is a long time..."
-captnron

While running a course on Seamanship Sail for Canadian Power and Sail Squadrons, a local rigger kindly came to speak. He stressed the importance of inspection and replacement, and stated that he thought that owners of older boats were often negligent about this.
"After all", he said, "what do you have that still works after 30 years?"

Whereupon a wag in the class replied "My wife still works, and she's WAY older than 30 years".

Fly_H23 · Aug 20, 2012

Would stainless chain plates in a fresh water only environment tend to last long? I just rebedded our O'day 26 and saw no signs of corrosion. Our boat has lived all it's life inland, 20 years at the same lake in Kentucky. Even still, I might just go ahead and replace them this winter...cheap insurance!

jibes138 · Aug 20, 2012

grades of stainless like 304 and 316 are not magnetic. passivation is mandatory if you want to keep the stainless properties intact. passivation removes microscopic contaminants that are corrosion sites waiting to happen. the manufacturing process of rolling out the sheet stock likely imbedded all kinds of stuff on the surface and into grain boundaries. Cutting the periphery and holes with water jet is good but water jet uses a grit for the cutting action. The passivation process also creates the initial anti corrosion film on the surface.

Ross · Aug 20, 2012

Fly_H23 said:
Would stainless chain plates in a fresh water only environment tend to last long? I just rebedded our O'day 26 and saw no signs of corrosion. Our boat has lived all it's life inland, 20 years at the same lake in Kentucky. Even still, I might just go ahead and replace them this winter...cheap insurance!

I have fifty year old stainless steel pots and knives and tableware that have never shown any sign of rust or cracking. I have stainless steel racks on the roof of my work car that are twenty years in service and have never shown any sign of rust dispite all of the winter road salt they have endured. There are good reasons that it is called stainless. Most of the times when I have seen rust stains on stainless steel it has come from transfer by abrasion against low alloy steel.

Cool Beans · Aug 20, 2012

Ross said:
Most of the times when I have seen rust stains on stainless steel it has come from transfer by abrasion against low alloy steel.

That's what the rigging company told me when I called to complain about some light brown hues and streaks on my new rigging and terminals. . .said it was most likely manufacturing residue and it would eventually go away. . .which is has so far. Definitely keeping my eyes on everything.

I made a new backstay CP and new uppers when I re rigged. The backstay CP was bent and had some stress cracks in it. The uppers I replaced because there wasn't enough "meat" for enlarging the clevis pin safely. I did discover some rust and a small crack in one CP below the welded on CP cover.

One neat thing I read to passivate and remove machine residue is to scrub parts down with Ospho. Every cut and drill hole would rust up bad even after a number of regular cleanings. . .one good scrub with ospho and they look damn good 18 months later

Just my 2 cents. . .

Stainless Steel Chainplates (failed 50 miles offshore)

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