Steel Keel

Discussion in 'Sailboats' started by HCB66, May 22, 2020 at 1:28 PM.

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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 at 2:17 PM
  3. Will Gilmore
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    Will Gilmore Junior Member

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  4. Yobarnacle
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    Yobarnacle Senior Member

    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

    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 Junior 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

    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

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