Lead Keel Bulb to Aluminum Hull

Discussion in 'Metal Boat Building' started by Vizy, Jan 22, 2022.

  1. Vizy
    Joined: Jan 2022
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    Location: UK

    Vizy New Member

    Good day all. I'll keep this short and sweet.
    Looking for your aluminum yacht building expertise: I am considering the idea of casting a lead bulb, hydrodynamically fair and bolt it to an aluminum fin shaped keel.

    Seeking advise regarding if this concept of attaching a lead bulb to an aluminum hull is common in yacht building (similar to a cast lead keel attached to a composite fibre hull) or just not good practice for fear of galvanic corrosion.?

    Appreciate in advance your time and knowledgeable comments on the topic.
    Cheers
     
  2. bajansailor
    Joined: Oct 2007
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    bajansailor Marine Surveyor

    Welcome to the Forum Vizy.

    Aluminium is anodic relative to lead, as per the table in this link, so you will need to have anodes (but you would need to have them anyway) -
    Metal Compatibility | Galvanic Corrosion Scale https://www.mfcp.com/technical-info/galvanic-corrosion

    Note though that lead is much closer to aluminium on the scale than stainless steel - and stainless steel is commonly used for fastening to aluminium (think of S/S bolts securing an aluminium toerail - but you will want to have a suitable sealant in between them).

    Rather than bolting the lead keel to the aluminium hull, would it be feasible to put the lead inside the alumnium fin keel? .
     
  3. Vizy
    Joined: Jan 2022
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    Location: UK

    Vizy New Member

    Hi Bajansailor
    Thanks for the welcome and your input.

    My go-to option is to fill the fin keel with lead bars. I also want as low as possible CG with a bulb shape to increase the volume/weight. My skills in shaping aluminum plate into a hydrodynamically fair curve is highly doubtful, thus considering a bolt on option to a standard fin keel.

    I was wondering if this is perhaps a common option in practice, taking into account sufficient epoxy sealant between lead, aluminum and S/S bolts, with all surfaces coated and antifouled. Would I still run the risk of galvanic corrosion or one should just avoid that option.

    Cheers
     
  4. bajansailor
    Joined: Oct 2007
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    Location: Barbados

    bajansailor Marine Surveyor

    Righty ho - can you tell us a bit more about your aluminium hull please?
    Is it an existing hull that that you are now modifying, or are you in the process of building it?
    If an existing hull, can you post a photo or two of it please?
    And if it is a new construction, and you have not started building yet, can you post a drawing of the boat showing the proposed keel arrangement?
     
  5. tane
    Joined: Apr 2015
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    Location: austria

    tane Senior Member

    lead inside the fin: 20 years is about the time when the likelihood of the fin corroding through fromthe inside out is increasing sharply. My choice would be: well insulated lead bulb bolted through with 3 grossly oversized bolts in shear (horizontal) without penetrating into the hull. (2rtws in 10 years on our (then) 37' roundbilge french Vaton designed keelboat.) well documented fact in french boating fora. "Our" keel corroded through on the new owner.
     
  6. AusVandestadt
    Joined: Jan 2023
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    Location: Qld

    AusVandestadt New Member

    Hey fellas
    I’m in the same boat regarding aluminium corrosion inside the keel. Some quick googling lead me here.

    I’m rebuilding a 48ft van de standt built in 1996, discovered the keel has been taking in salt water and cut off the leading edge to investigate ( attached some pictures below)

    I’m planning on removing the keel and having a new keel fabricated, with a bulb. Or the majority of the weight down low.
    Was wondering how you guys went with this project and if you can offer any advice


    Thanks I’m advance !!
    Nick
     

    Attached Files:


  7. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    Welcome to the forum AusV..

    Wow, that's some pretty bad corrosion in there...
    Once fabricated, best to paint the interior surfaces with white epoxy, as a seal.
    In the "old days" such inaccessible regions of structure used to be oil filled and sealed, for said reason.
     
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