Isolating Keel Bolts at Flange

Discussion in 'Metal Boat Building' started by SeaJay, Dec 1, 2009.

  1. apex1

    apex1 Guest

    That was a very dumb mistake I made there, sorry for that!
    I deleted the post.

    Regards
    Richard
     
  2. tazmann
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    tazmann Senior Member

    Sea Jay
    I cant tell in the picture but are the bolt heads resest in the flange and faired over with filler or exposed ? moisture migrating around the the bolts shouldnt be an issue if you fill with marine caulking " no air void around stem of bolts"
    Tom
     
  3. SeaJay
    Joined: Jun 2007
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    SeaJay Senior Member

    Tom,

    My keel is similar to the one in the photo, but not exactly the same. The bolts will be inside "pockets". My plan is to epoxy coat the flange and the inside of the bolt holes. Between the flange and hull, I'll use a sealant as typical, with special attention around the bolts themselves. After the keel is in place and the bolts tightened, I thought I'd put a "grease cap" over each bolt. After that is done, I'll foam the pockets and seal them with epoxy/glass.

    I think water intrustion from the pockets should be limited, but my concern is more from the joint between the keel and hull. It would seem to me that is just the environment where stainless has a problem with crevice corrosion and pitting. This was why I was leaning toward monel, but then you get the galvanic corrosion between the bolts and the steel flange...damned if you do, damned if you don't.

    Regards,

    SeaJay
     
  4. tazmann
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    tazmann Senior Member

    SeaJay
    I see what you mean damned if you do and damed if you dont. I wouldnt use stainless there eather with only part of the bolts being exposed to the inside of boat. If the keel fits nicely to the hull and the surfaces are painted with an underwater epoxy then when you put in on use a thin layer of marine caulking on both surfaces, bolting it up tight will squeeze the excess caulking out. Good tight seal with no air voids you would never have a problem unless the keel came loose some how? I think the only place you will have problem with corosion is the nuts washers and exposed threads on the inside of boat but thats easily taken care of paint ,grease ext.
    Tom
     
  5. SeaJay
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    SeaJay Senior Member

    Eric,

    I have some preliminary pricing info. (I asked for a quote on Duplex 2205 as well as 17-4 or 15-5 (Aquamet type material) if they had it. Here is the response to my 3/4" x 12" inquiry:

    Bolt in 2205 duplex $80.00E Nut $12.00E Ship in 2 weeks after receipt of
    order. The other materials would be wildly more expensive


    (At $92.00 per set, one can only imaging what "wildly more expensive" means!)

    By comparison I found a 3/4" 6" 316 ss (not 316L) bolt for $12.00. Figure maybe $25 for a 12" bolt and $5 for the nut, and it's about 30% of the Duplex 2205. For my application that's about a $850 difference...hmmm, I'll have to think about this.

    SeaJay
     
  6. SeaJay
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    SeaJay Senior Member

    I'm baaaaack

    (6 months later) I've been out bolt shopping and the difference between what engineering calcs call for and what is available in the real world has reared its ugly head. As noted earlier the costs of the duplex and monel (if you can find them) bolts are enough to give one pause. And even after all of that, I still have the crevice corrosion and galvanic corrosion issues that I've noted before.

    So tell me if I'm nuts...what about just using Grade 8 steel bolts and coating/embedding them in epoxy? I can get 12" x 1" Grade 8 bolts from McMaster-Carr for $18.66 each (interestingly, the same bolt zinc coated is only $13.08...go figure!). The Grade 8 steel is as strong or stronger than the other options and crevice / galvanic corrosion are not an issue. Of course I still have steel in salt water, but it isn't like that is an unknown combination. And remember, my bolts are easily accessable for inspection and/or replacement.

    What say you gentlemen?
     
  7. Brent Swain
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    Brent Swain Member

    The easily accessible is the key. You can check them early after lauching then less often if problems don't appear. If there are major problems, they will show themsleves quickly.
    Grade 8 bolts seem your best choice at the moment. Zincs will protect them outside , inside should be checked regularly, where zincs wont protect them. The only safe way to guarantee contact with a zinc is to weld them on.
     
  8. TeddyDiver
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    TeddyDiver Gollywobbler

    Agree with Brent in this one :)
     
  9. Brent Swain
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    Brent Swain Member

    For bolt on zincs, where I don't have the opportunity to weld them on right away, I like to use welded on stainless bolts, and put a bit of ss weld around the bolt hole on the zinc strap. That way, you have stainless in contact with stainless, with far less chance of a bit of corrosion insulating the zinc from the hull. Then I get a welded tack on it at the first opportunity.
     

  10. SeaJay
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    SeaJay Senior Member

    Thanks for the input Brent.
     
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