lag time

Discussion in 'Sailboats' started by lat 64, Aug 12, 2009.

  1. lat 64
    Joined: Aug 2009
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    Location: alaska

    lat 64 Junior Member

    I have a good question for a stupid design.
    I have an old lead keel with bad, bad, bad, rusted bolts.
    The best information I can get on this boat is that they used 3/4"-dia. lag studs, 9"-long for keel bolts. This has held up for 41 years, but they are so rusty it scares me. There is no crack in the keel joint and no leakage so I feel the design did work. According to the original plans, the studs are supposed to be only 5" into the lead keel, with 4" exposed. They are not cast in place. The factory just drilled and tapped for the lag threads, drove them in with a little kerosene, and went sailing.
    I want to replace or sister these with silicon bronze. I know,I know, through-bolts are better. but I should do something soon.
    The question is:
    Are there specs for how deep I should drill for new lag bolts, and what thread size should I use.
    The keel ballast is 5,000lbs. and there are nine bolts.
    I can get bolts custom made right here if I bring enough highland malt to the machinist.

    Cheers from Alaska,

    Russ
     

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    Last edited: Aug 13, 2009
  2. alan white
    Joined: Mar 2007
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    alan white Senior Member

    Removing them would be ideal, and then replace them with bronze or stainless.
    One thing you might do is to make a 10" drill from a pipe that's a bit larger inside than 3/4" and drill the lead from around the studs. Maybe a carbide hole saw carefully cut and welded to the appropriate sized pipe. Then pour epoxy into the holes (which are now over an inch diameter) and redrill--- this time all the way through, and nutted. The floors would have bigger holes too, so they too would require filling with epoxy.
     
  3. lat 64
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    lat 64 Junior Member

    Alan,
    Thanks for the post. That would be clever way to extract the existing bolts.
    This boat has a fin keel and there is about 3 feet of lead to go through if I were to drill all the way.
    I'm looking to use the same method as factory but upgrade the bolts and hole depth a bit—or maybe just haul out next year and drill for all I'm worth til I hit the dirt and put in long rods of bronze.

    But right now I am wondering if there is any specs for pull-out strength of screw threads in lead:?:
    It turns out that Defender of 1896 was built this way and it was controversial then too.

    Russ
     
  4. alan white
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    alan white Senior Member

    Russ, threads come in all sizes. Once the holes are drilled over-size, it would be a snap to thread those holes (maybe after redrilling to the proper tap-ready size, like whatever is required for 1 1/4".
    Sounds big, but the cost is in the metal only and if you wanted a bit more security than the original offered, the bigger diameter studs would do that.
    They are, after all, only 9" long.
    Easy tapping, too.
     
  5. lat 64
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    lat 64 Junior Member

    recycled shaft

    I found out today that my machinist buddy has an old 1-1/4" bronze boat shaft that we will probably cut three studs from.
    We calculated that we could have as much as 13,000 lbs shear strength in the lead keel with a 1-1/8 threaded stud five inches in. If I put in three new studs, I would have 29,000 pounds of keel holding. and along with replacing the original lag bolts, maybe over a gazillion tons.
    I think I would actually set them deeper—eight inches or so. I am now thinking that one could actually make a good repair and upgrade without hauling out.
    But that's not ruled out yet either.
    I have to spend some time confirming these numbers before any plan is made.

    r.
     
  6. Frosty

    Frosty Previous Member

    Your going to tap a thread in lead?


    My mind is going nuts at the thought of this. What about drilling a 1inch hole straight through the keel approx 5 inches (or more) down from the top and pass a steel bar with 2 threaded holes along the length of the bar for say 2 keel bolts.

    4 or 5 of these would give you attachment strength,--better than tapping thread in lead.
     
  7. alan white
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    alan white Senior Member

    Read about the 3 ft fin keel. The boat's pretty old, and all he's doing is vastly improving on the original setup, which used 9 threaded rods going in a mere 5 inches. It ought to be strong enough, though it seems at first to be a little sketchy, being so shallow. One thought is, the plans show they are 9" long, and 5 inches into the lead, but the builder might well have gone a lot longer than that since he may have been more paranoid than the designer.
    Think about that, Lat64
     
  8. lat 64
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    lat 64 Junior Member

    Yea, The thought of making a mechanical connection with something as soft as cheddar cheese is alarming for sure. But it seems that is what the factory did 41 years ago, and the keel is still on with no visible failure yet.(the night is young).
    My thinking is to restore and upgrade the original system by a factor of at least 2.

    The toggle idea of yours(frosty) is worth considering as an option because it leaves out all the calculations for shear strength and thread surface area as I am new to that stuff but my buddy is not.

    The blueprints that are in my owners manual have notes that call for that lag bolt design, but I really have to groundtruth it before proceeding.
    The records are poor about keel design on a Columbia 36 and who knows what is really in there. The placement and style of the bolts visible is just as called for in my copy of the plans.

    I was writing when alan's post came through.

    The desinger was Bill Crealock and the buider was columbia under the direction of Dick Valdes

    Thanks guys. This is getting interesting for me. G'nite,
    R
     
  9. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It's perfectly acceptable to use lags on ballast keels, though more often they are machine thread. Of course it wouldn't on a high aspect, bulbed appendages, but the Columbia 36 isn't one of those.

    Removing the lags may prove troublesome, but heat can come to the rescue, if brut force doesn't convince them to turn out. It usually takes careful use of heat and an impact wrench.

    You can tap lead, but it has to have antimony added during the pour (maybe 3%) or you'll have hell to pay drilling and tapping. The general rule is 8 times the diameter of the lag in depth of the hole. You wouldn't be wrong to go deeper. Since the lead was tapped, you could expect it to have antimony, use plenty of oil and back out often to clear the bit, trust me you don't want it to grab.

    Through bolts are wonderful, but not always necessary and certainly a lot more expensive.
     
  10. Frosty

    Frosty Previous Member

    What about those bolts that expand that they use for concrete. Get one of those buried in the lead!!!!

    How can you tap 8 inches deep?
     
  11. Luckless
    Joined: Mar 2009
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    Luckless Senior Member

    Use a tap head with a shank longer than 8 inches.
     
  12. wardd
    Joined: Apr 2009
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    wardd Senior Member

    here's a possible idea

    after the bolts are extracted and the holes drilled out for the new bolts cut holes in from the side to meet the bolt holes at the bottom, side holes big enough to slip in nuts and washers use thread locker

    slip in nuts and washers and insert bolts and screw into nuts, fill cavities with molten led or epoxy

    and a good grade all thread could be used
     
  13. Frosty

    Frosty Previous Member

    Then you would need to drill new holes in the boat.
     
  14. wardd
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    wardd Senior Member

    use the same locations in the keel for the bolts

    maybe this is the confusion the nuts go in from the side of the keel or squares of tapped steel
     

  15. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    This isn't rocket science folks and frankly it's done daily some place in the world.

    Remove the hanger bolts, which will take some persuasion, then use new hanger bolts or slightly deeper bolts if it makes you feel better. If you want over size then drill, slowly, lots of oil and by someone who's drilled lead more then once before.

    Nothing needs to be reinvented or re-engineered, it's just a ballast bolt replacement job, what's the mystery?

    Sure a high aspect fin that's half the displacement of the yacht would require a different approach, but have you seen the keel on Columbia 36, let alone appreciate the ballast ratio on this yacht?

    The only questions (curiosity) I have concern the model (MK II?) and the type of fin employed, though they were all attached the same and the to the same hull stub.
     
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