Keel bolt composition

Discussion in 'Fiberglass and Composite Boat Building' started by Roly, Jan 21, 2012.

  1. Roly
    Joined: Jul 2005
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    Location: NZ

    Roly Senior Member

    I am putting the keel back on after a rebuild.
    It is a mild steel (or Corten) steel plate (3m) with a steel
    grid system to lead ballast.
    Old bolts were galvanised steel painted & 80% were fine after
    30yrs.

    When pondering whether to go the same path (proof of service) I read this:

    If we are asked to replace keel bolts on an iron keeled boat, our order of preference of what we can source currently is;

    1 Ductile iron
    2 316 0r Aqua-met
    3 Galvanized Steel
    4 Mild steel


    Ductile iron ? ye olde world sizing, hard to source (for me), have to make fittings.

    2,3,4 relatively easy. Why is aquamet & 316L so high on the list?
    Bolts will be fully encapsulated in epoxy, but one will be a lightning ground.
    Is crevice corrosion that prevalent or somewhat overblown?
    What would you use?
     
  2. keith66
    Joined: Sep 2007
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    Location: Essex UK

    keith66 Senior Member

    Im in the middle of dropping the iron fin keel on my Sabre 27, shes grp & 40 years old. As she has spent virtually all her life in a mud berth i figured it was time to do it as she was leaking from somewhere near the forward bolt 7 there were signs of movement.
    According to spec the 7 one inch whitworth studs are high tensile steel & were glassed over, on grinding the grp caps off i found the nuts & large plate washers were black with virtually no corrosion. It took a large air wrench to shift the nuts & the threads were still shiny. What i will find when i jack the boat of its keel im not sure.
    As for stainless a friend fitted 316 bolts to his wooden gaff cutter (lead keel) & five years later had to pull one for insurance survey, crevice corrosion had propogated into a long zigzag crack & it was actually sheared off. Of the 12 bolts over half were the same. I wouldnt risk it through oak.
     
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  3. michael pierzga
    Joined: Dec 2008
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    michael pierzga Senior Member

    Galvanized steel is strong, long lasting and a very good choice. Normally the only corrosion problems are internal..in the bilge. Protect the bolt heads from sea water contact.

    Why change ?? SS has problems too
     
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  4. gonzo
    Joined: Aug 2002
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    Location: Milwaukee, WI

    gonzo Senior Member

    Galvanized steel is a good choice. If you can get thirty years more, it is not a bad deal. If you paint them with a flexible coating, they will last even more.
     
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  5. Roly
    Joined: Jul 2005
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    Location: NZ

    Roly Senior Member

    Suits my pocket too.
    I will get ms round stock, thread to size, & then hot dip.
    Thanks guys.
     
  6. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    See if you can keel the bolt heads out of bilge water with a spacer. even 10mm will help . Use best craftsmanship when bedding the keel and bolts.
     
  7. Roly
    Joined: Jul 2005
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    Location: NZ

    Roly Senior Member

    As much as I didn't want to have them visible, I preferred to have the keel bolts protrude
    through the floors with the sole recessed for them; So they are well out of the bilge and distributing the load over a broad area. I will build a cover so as not to trip on them. The floor grid has oversized holes which will be filled with epoxy.

    Not the best cosmetically, but better structurally imo.
     
  8. tunnels

    tunnels Previous Member

    so how goes the build ?? i been away a while and hope to be back in nz for a week or a little longer soon if i get time i would like to drop in and see your progress . I question the choice of filling with epoxy i think there a better way , could have a hell of a job getting the keel off if you ever had to !!!
    Keep at it !!. :p
     
  9. michael pierzga
    Joined: Dec 2008
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    Location: spain

    michael pierzga Senior Member

    Nothing wrong with bedding the keel into thickened epoxy. Just make sure to use a realease film on one surface. Brown mylar packing tape on the top of the keel works for small keels. A keel must not be "glued " to the hull...it must not transfer loads into the hull skin.

    A good size radius fillet of bog at the keel hull joint keeps things looking good.

    Epoxy bog is the only way I know of to remove build inacuracys from the hull keel joint. To be succesful this joint needs perfect mating surfaces..like an engines head to block.

    In future when removeing the keel if the keel bolts handup because of bog or because the bolts are not parrelel....simple make a home made holes saw ...thin wall...slide over the keel bolts and bore.
     

  10. Roly
    Joined: Jul 2005
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    Location: NZ

    Roly Senior Member

    Hey tunnels,
    Real slow only odd days here & there.
    Pretty standard procedure I thought to mate with thickened epoxy (With a bond breaker) I was going to wax the bolts
    present, cure & then drop the keel a little, remove wax, and use coal tar epoxy or sealant around the bolts/joint. But I think I prefer Michaels method & use an extended hole saw over the bolt, to remove. (KISS priciple)

    The old keel was glassed to the hull. Is that a no-no? ( Plus 12 M12 galv bolts)
     
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