Corrosion in unstayed mast step - how bad?

[MizDiana]

I made an offer on a Freedom 33 (note: unstayed cat ketch design) and am currently doing a self-inspection. So far the boat looks better than I expected, though there is the usual electrical wiring mess. However, I've run across corrosion in the mast steps. This is not at all my area of expertise, and I'm pretty ignorant.

Background: being an unstayed design, the forward main mast is stepped into a below-decks fiberglass bulkhead and the mizzen mast is keel-stepped. They have very strong deck collars that appear to be in good shape, though also have some very light surface corrosion.

I believe the deck collars & mast steps are all of roughly the same design, in aluminum. Probably with steel bolts. They're also holding (painted) carbon fiber masts - carbon fiber can be a cathode for a galvanic reaction.

This being something I'm ignorant of, I don't know if I'm looking at a serious problem or nothing at all.

[MizDiana]

Here's an image of one of the deck collars (in better shape).

[boatpoker]

The step collar does appear to be suffering from galvanic corrosion. The 4th photo is particularly concerning. I'd suggest you find a surveyor who is also ABYC Marine Corrosion Certified to have a closer look at it.
PS. I'm a retired ABYC Certified Marine Corrosion tech.

[psk125]

Agree with BP - It would be better if whatever's going on there weren't. The mast looks OK but the step appears to need replacing. What to replace it with is another question. Wood might be less problematic if it can be made strongly enough.

[boatpoker]

Originally Posted by psk125

Agree with BP - It would be better if whatever's going on there weren't. The mast looks OK but the step appears to need replacing. What to replace it with is another question. Wood might be less problematic if it can be made strongly enough.

Aluminum in direct contact with wood will suffer from poultice corrosion.

[Ixium]

https://imgur.com/gallery/7HPFlwQI have a freedom 39

The previous owner owned the boat for a long time before and did the mast steps a while ago. It’s almost been 19 years and they look better than what those pictures are

https://imgur.com/gallery/7HPFlwQ
Are the blue prints I have for mine

Considering there isn’t much holding the mast to the boat, I’d get them fixed up before any serious sailing.

If you have access to a gin pole I don’t imagine it being that hard depending on your skills. Unbolt it, pull it up a foot above deck if you need to change deck mounts too, then bolt it back down.

[barnakiel]

Machine or cast a new one. Avoid alloy (alu). You can also form one in carbon and vacum it. Custom build, but a simple one.


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[grantmc]

No need for experts, the pictures show clear signs of significant corrosion.
Consequence lot and lot of money!
Run away, run away, run away.
Where is that list of boats for sale we're checking out?
Can cross another off!

[barnakiel]

I will disagree on the cost. It is a basic mechanical part that can be cast or machined easily by any moderately skilled person.


We at times demonize repairs. Then we find people did the repairs and never looked back.


The step does not need to be alloy, and likely should not be alloy, given the mast material.


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[boatpoker]

Originally Posted by barnakiel

I will disagree on the cost. It is a basic mechanical part that can be cast or machined easily by any moderately skilled person.


We at times demonize repairs. Then we find people did the repairs and never looked back.


The step does not need to be alloy, and likely should not be alloy, given the mast material.


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What material do you recommend to eliminate or at least minimize a galvanic reaction with the carbon fiber ?

[Bowdrie]

First some tongue-in-cheek:
Boeing is laying people off, get one of the guys who worked in "Mockup", he can take some pre-preg and an autoclave and make new steps and collars.

With that out of the way, the pics show that there was an attempt to use some kind of tape product to insulate the masts from the steps.
It also appears that water had been sloshing around in the bilge.
With the carbon masts, the aluminum steps, and the stainless bolts, everything was in place to make a couple of nice batteries, you can't get much further apart than carbon and aluminum.
Even when the salt water was gone salt still remains and the rain water coming down the mast thru the leaking collar just started the whole process again.
Speaking of the deck collar; it appears that whoever tried to seal it was someone who's abilities are not-quite-ready-for-prime-time.
PS: That green bonding wire likely wasn't helping things much, with water trapped in the step, (or in the bilge,) the aluminum step became just another sacrifical anode like the zinc on your prop shaft.

[psk125]

Originally Posted by boatpoker

Aluminum in direct contact with wood will suffer from poultice corrosion.

OP says the masts are Carbon Fiber. Would replacing the aluminum step (removing all the aluminum) with a carved wooden block not work OK?

[boatpoker]

Originally Posted by psk125

OP says the masts are Carbon Fiber. Would replacing the aluminum step (removing all the aluminum) with a carved wooden block not work OK?

That was not a well thought out response by me ... brain fart ... However, I'd be concerned about a block of wood taking those side loads. I'd want an engineering opinion before using wood or even a carbon fiber step.

[GordMay]

Originally Posted by boatpoker

What material do you recommend to eliminate or at least minimize a galvanic reaction with the carbon fiber ?

TITANIUM [Ti]
Commercially pure Titanium [and its alloys] are almost completely resistant to galvanic corrosion, when they are coupled with carbon composites [carbon fiber reinforced polymers, or CFRPs]. Ti has the most positive OCP of all the engineering metals, and thus, its potential difference from carbon is much smaller than steels, Al alloys and Mg alloys. In theory, its galvanic corrosion, in contact with CFs or CFRPs should be relatively insignificant.

“Galvanic corrosion property of contacts between carbon fiber cloth materials and typical metal alloys in an aggressive environment” ~ by Z. Peng, X. Nie
➥ https://www.sciencedirect.com/scienc...57897212011061


The most common solution, to preventing corrosion between the two materials, involves creating a physical barrier, or isolation point, between the two conductive materials. This can be achieved a few different ways.
Fiberglass can be added to the layup where aluminum core meets core fiber, or where CF & Aluminum substrates may be bonded together.
Epoxy primers, paints, and adhesives are often used to create a barrier between metals and carbon fiber. Another option to prevent corrosion between carbon fiber and aluminum is to encapsulate the bonded areas, where neither water, nor moisture in the air, can get to the bonded surfaces.

[barnakiel]

Originally Posted by boatpoker

That was not a well thought out response by me ... brain fart ... However, I'd be concerned about a block of wood taking those side loads. I'd want an engineering opinion before using wood or even a carbon fiber step.

If it is the right wood, there is no problem. But wood may/will hold moisture, hence an imperfect material - in the bilges.


Plain epoxy/glass block will do. Laminated to required thickness, then machined to form the step. Does not hold moisture and does not conduct.


Bit of a shame the design did not have grp steps molded in. Then bolts could be completely avoided too.



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