Toe Rail / Stanchion base Electrolysis Repair Suggestions?

[Bob Pullen HC-33 1981]

Pulled a stanchion off the toerail and found this!! (picture is looking down at outside deck & toe rail bolts after cleaning out the corrosion - Seanorita is a 1981 Hunter 33)
Cracks are not all the way through to outside of toerail. Bottom of toe rail is eaten all the way through. Fiberglass still in good shape as well as seam.
Possible reasons: P.O. spent many years in small marina, small basin, lots of boats not well maintained, and about 6 years too derelict to change zincs.
Any ideas on repairs which might not involve pulling the toe rail?
Thinking of a strip of aluminum across the top with the 2 toe rail bolts through it, with lots of epoxy & fiberglass buildup under it?
Many thanks,
Bob
S/V Seanorita

 

[sailcruiser]

Are you sure it is electrolytic corrosion ( ie stray current) from either your or other boats? Does your boat have either a galvanic isolater or isolation transformer? Could this be galvanic corrosion between dissimilar metals?

If it were my boat I'd make sure to fix how it happened in addition to the damage.

Good luck! SC

 

[Steve Dion]

Re: Toe Rail / Stanchion base Electrolysis Repair Suggestion

I think I would agree with SC. This is probably galvanic corrosion from having the stainless steel stanchion in contact with the aluminum toe rail. In the future you may want to consider getting a piece of mylar or similar thin plastic to seperate the contact between the two metals. You will also want to use tef-gel or some similar product to coat the s.s. screw going into the toe rail.

 

[AtlanticAl]

Re: Toe Rail / Stanchion base Electrolysis Repair Suggestion

Its zero to do with anodes on the boat, its bad design. If the rest of the stanchions contact the toe rails you will have the same problems there. You have stainless steel, against aluminum, the aluminum being the weaker metal becomes the sacraficial metal, the electolyte to pass the current across, is the salt water, or even any water that is not pure water, free of any contaminants, which outside of distilled water, dosent exist.

My advice would be, "unless you want to buy new toe rails" grind the rotten part out with a dremmel, it will look a lot worse than it is, because the way aluminum corrodes, its outer layers, expand to severeral times their thickness, and it looks bad, but once you grind it off, are down to polished metal, their is still a lot of metal there.

When you put the stanchions back, some suggestions above, but problem will be with bolts, you have to isolate the bolts from the aluminum, or use aluminum bolts, which will become the sacraficial anodes, as they will be corroded by the stainless.

Their is no easy fix, its bi-metalic corossion, and the inferior metal, is the one that is always eaten away. But on a plus side, its taken since 81 for that metal to get eaten away, so some simple repairs will last it another ten years.

 

[Cayennita]

Re: Toe Rail / Stanchion base Electrolysis Repair Suggestion

I had a similar problem in my old Beneteau. I cut out the base portion of the toerail and made up a backing plate with the socket base through bolted. After installing the stanchion a drill through the toe rail and the stanchion and bolted with an acorn nut in the inside.

 

[Bob Pullen HC-33 1981]

Re: Toe Rail / Stanchion base Electrolysis Repair Suggestion

Thanks for the clarifications!
Having very little experience with anything electrical I had been led to understand that the corrosion between dis-similar metals is sped up by a lack of grounding or isolation of a boat's electrical system, which was evident on this boat (no internal grounding wires could be found, ample evidence of lots of electolysis or galvanic corrosion all about - not than I claim to understand the lack of relation between the two). We have since addressed this by someone with a bunch more experience than I ever care to have.
Now the repair work.
Yes, I agree, the design lacks a bit of forethought, but I will have to address each of them, and yes, we appreciate the suggestions on how to isolate this dis-similar metal junction, and will duly follow said advice.
Thanks again for any suggestions, ideas, and advice.
We have 7 more stanchions to look at.
Oh joy!!
cheers
Bob

 

[sailcruiser]

Bob good luck. I'm chasing an issue on my boat which is likely a shore power issue but I'm going through everything to be sure. Just a side note on 'electrolysis' some folks get their knickers in a knot with this term. I was told at some point something to the effect 'electrolysis is what women do to their legs'. I guess it's an overused inaccurate term.

Isolating the metal is important. I wonder if some dielectric grease would help on the bolts. There are quite a few around here more educated than I on this subject. I'm not sure why aluminum bolts would be bad if you are a) protected from your neighbors on shore power and b) free of stray current yourself.

If you do plug in to shore power make sure you have a galvanic isolated or isolation transformer and check that your anode is the correct material. Zinc or aluminum in salt water and magnesium and aluminum in fresh. Magnesium should never be used in salt. Zinc becomes useless in fresh quickly.

For backing played I've used fiberglass successfully. Are your stanchions connected to your ground point? SC

 

[rardiH36]

Thanks for the post. Reminds me that I moved on to some other repair category before I finished the last of eight stanchion/toe rail remediations on my 1980 Cherubini Hunter 36 which has the exact same fittings as your 33. Got to do it.

As to why the unsatisfactory design, maybe Hunter thought that the aluminum anodizing would be a sufficient non-conductive barrier to prevent galavanic corrosion. Probably worked for a while ...

My toe rails had not corroded all the way through. I did my best to scrape/grind away most of the oxidized Al. Then filled the depressed area with fiber thickened epoxy until relatively flush with the undamaged toe rail on either side. Also before reassembling, I placed a couple of layers of electrical tape on the vertical stanchion/rail interface. Hopefully this will retard future corrosion.

 

[Bill Roosa]

Re: Toe Rail / Stanchion base Electrolysis Repair Suggestion

Just a recommendation. Aluminum and SS can live together IF (and it is a big IF) you do not have an electrolyte like salt water, typically from splashes.
a fresh water wash down will remove most of the salt and greatly slow down the corrosion process.

 

[Bob Pullen HC-33 1981]

Re: Toe Rail / Stanchion base Electrolysis Repair Suggestion

Sounds like some great advice.
No the stanchions are not grounded (no evidence of any wire anywhere around them)
Not sure about the galvanic isolated transformer, but will check further.
We are doing the epoxy, filler, build up.
Got a very thin aluminum plate to bridge the 2 toe rails above - also adding a stainless backing plate below the 2 toe rail bolts (inside cabin).
Isolating material (using 1/8 high density polyethylene) also being added for isolation.
thanks again
Bob