Steel Keel

Discussion in 'Sailboats' started by HCB66, May 22, 2020.

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  1. HCB66
    Joined: Oct 2017
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    HCB66 Junior Member

    I'm looking at a fiberglass boat with a bolted on steel keel. It's pretty rusted and would need a lot of grinding, new bolts etc but even if I got all that done I'm wondering if this is something I can just glass over once it's clean or will water just find it's way in and rust it out anyway?
     
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Is it actually a fabricated steel keel?
    I think it is more likely to be a cast iron keel.
    Re glassing it over - I am sure that others on here will also say 'don't even think about it'.
    You will NEVER get the cast iron (or steel if that is what it is) clean enough.
    If you do buy the boat, you will probably have to regard maintenance on the keel as a necessary evil.
    Can you post a photo or two of this keel please?
     
    Last edited: May 22, 2020
  3. Will Gilmore
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    Will Gilmore Senior Member

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  4. Yobarnacle
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    Yobarnacle Senior Member holding true course

    I know a little bit about maintenance on steel vessels. Spent fifty years of my life aboard steel vessels.
    Rust isn't a bad thing if controlled. Blueing on gun barrels is a controlled rust process. a tiny bit of blood on the blueing will mar it.

    Practical application. Large vessels go on drydock once every five years. Required by law. It's expensive!
    Using very high pressure water blasting (allows collecting and filtering the run off which air/sand blasting can't be done) the dright metal bottom is deliberately allowed to sit overnight and develop a film of fresh surface rust. Why? It improves bonding of the epoxy to be applied. it makes the steel surface microscopically rough and craggy, for the epoxy to infiltrate and latch on to. After several base coats of epoxy, the anti-fouling coats are applied and the vessel relaunched for five more years of service.

    The epoxy seals the surface so oxygen can't reach the steel. No oxygen, no additional rusting. the thin surface rust the epoxy was applied over, does not grow. it's not a desease. Seal the steel, and no rusting occurs. that's what marine coatings are designed to do. Did you think paint was merely cosmetic? Hope that's helpful
     
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  5. Yobarnacle
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    Yobarnacle Senior Member holding true course

    some how bright steel became dright steel in above post.
    Two kinds of rust. Ferrous oxide FeO and ferric oxide Fe2O3. You get both kinds. the important part is the O. Oxygen. Eliminate the oxygen, rust is impossible.
     
  6. Will Gilmore
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    Will Gilmore Senior Member

    From the National Association of Corrosion Engineers (NACE) website
    Pitting Corrosion - NACE https://www.nace.org/resources/general-resources/corrosion-basics/group-1/pitting-corrosion
    "Pitting is initiated by:

    a. Localized chemical or mechanical damage to the protective oxide film; water chemistry factors which can cause breakdown of a passive film are acidity, low dissolved oxygen concentrations (which tend to render a protective oxide film less stable) and high concentrations of chloride (as in seawater)

    b. Localized damage to, or poor application of, a protective coating

    c. The presence of non-uniformities in the metal structure of the component, e.g. nonmetallic inclusions.

    Theoretically, a local cell that leads to the initiation of a pit can be caused by an abnormal anodic site surrounded by normal surface which acts as a cathode, or by the presence of an abnormal cathodic site surrounded by a normal surface in which a pit will have disappeared due to corrosion."

    Where they talk about damage to the protective oxide film, they are referring to a protective film of corrosion that protects steel, especially s.s. and aluminum and copper, etc. from further corrosion by cutting off the oxygen. If there is damage to this coating, corrosion begins again and the coating is repaired, however, if there is damage to this oxide coating and the environment lacks the oxygen to repair the damaged area, a pit corrosion point can grow. Low PH contributes, as does the presence of salts, which leads to high PH. In that case, the pit can become anodic with respect to the surrounding cathodic material. This is most likely where there are tiny defects in the alloy material. In that case, micro cathodic cells can form and putting can grow because of the lack of oxygen.

    I can't speak with authority here, but I suspect the the reason the bright metal was allowed to sit overnight was to develop that protective oxide coat, not for better adhesion. A quick buff of sand paper would do that.

    -Will (Dragonfly)
     
  7. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Hmmm. Which is more cost and time effective. waiting overnight for a rust film to develope. or light hand sanding of a thousand foot long, hundred foot beam hull? :)

    Or even a 220 ft long X 50 ft beam deepsea tug hull? i have sailed many vessels over 700 feet in length including thousand footers. worked my way up from ordinary seaman to master. did alot of prep and painting topsides myself.

    US Flagged Towing Vessels https://ottocandies.com/us-flagged/towing-vessels/

    my favorite ships were big tugs. Only Master of Towing is allowed to handle multiple vessels simultaneously. more interesting. Advanced ship handling.
     
  8. Yobarnacle
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    Yobarnacle Senior Member holding true course

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  9. David Jones
    Joined: May 2020
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    David Jones Junior Member

    Kinda there, there are typically three kinds of rust in the steels you are talking about, Fe2O3, Fe3O4 and the FeO. (this is a simplistic explanation - there's lots more...) Those are also know has hematite, magnetite, and wüstite. These names are commonly applied to ore, however the first two are the common forms of rust seen from steel sitting in air.

    FeO, is a high temperature oxide, you will have more likely seen it in steel coming from a mill/steel supplier. It has a dark almost black appearance. FeO, is an oxide more closely structured to aluminum oxide, a hard non-porous adherent oxide that does not promote further oxidation. It would be great if it wasn't a high temperature oxide as then we could make our steel be more like aluminum in resisting oxidation, but alas, it doesn't form anywhere near room temperature. It doesn't start forming until above about 580 degrees C.

    Fe2O3 has the difficulty that it is very porous, and attracts water. This leads to Fe2O3 typically with lots of H2O. The porous structure creates capillary action pulling the water down to the surface of the steel, where the water dissociates, freeing the oxygen, and the iron continues to rust. this rust is often considered self-propagating. this is also often called "red rust".

    Not that any of this really matters to this discussion, just thought I'd add a bit to the oxides mentioned.

    The rest of what was said is really great...

    dj
     
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  10. HCB66
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    HCB66 Junior Member

    I appreciate the replies they'll probably also help others on here. I won't be buying this boat though it was an old trash boat that they were selling for 400 dollars. I emailed the guy and suddenly he emails me back saying the whole thing boat and trailer goes for 1000 dollars. Just like I had not seen the original add for 400 dollars or something. Knew something crooked was afoot so I backed out of that real quick.
     
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  11. Yobarnacle
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    Yobarnacle Senior Member holding true course

    Whatever boat you eventually acquire, I wish for you,and predict that you will have success with it. How can I predict success? Because you exhibit prudence and good judgement. Prerequisites for "good luck". Common sense isn't common at all, but you got it! :)
     
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