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Fastening a BDS together

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  • futabachan
    Okay, I think I finally have a workable solution for fastening the sections of a Breakdown Schooner together, and as a bonus, I d only need to haul her in two
    Message 1 of 1 , Mar 1, 2002
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      Okay, I think I finally have a workable solution for fastening
      the sections of a Breakdown Schooner together, and as a bonus,
      I'd only need to haul her in two trips, not three. Ironically,
      now that I've solved the major roadblock, I may wind up never
      building her, given the existence of the Insolent 60. Anyway....

      If you look at the side elevation of the BDS in BWAOM, the
      amidships section is shaped like an upside-down letter T, with
      an 8 foot superstructure sitting atop a 20 foot long ballast
      tank below the waterline. There are a pair of bolts through
      long metal brackets attached to the superstructure at the sheer,
      and a little skeg that the end of the ballast tank hooks into
      on the bottom. The superstructure consists of two big boxes
      that serve as storage bins and cockpit seats, which sit atop
      the ballast tank. The cockpit floor is suspended between them
      over a floodable well; the centerboard runs down the middle of
      the well, supported by triangular wooden brackets.

      Bolger's suggestion for improving the fastening system involves
      adding two giant U-shaped metal chain plates at or near the ends
      of the ballast tank, that would run up to the top of the cabin
      superstructure and fasten with huge transverse bolts. My ideas
      on the subject tended to involve adding an extra set of horizontal
      bolts either externally at the chine, at the bottoms of the
      cockpit seat storage bins, or just above the waterline, and two
      sets of vertical bolts through the floor of the salon and hanging
      locker.

      I'll try to scan in some simple sketches over the weekend, but
      the problem with running the vertical bolts is that the holes
      compromise the watertight integrity of the bow and stern sections,
      which I'd really rather avoid, and puts you on the clock when
      fastening the boat together. Extending the ballast tank to the
      waterline level or above would fix the problem, but would require
      a fairly serious redesign and rob the cabin of some headroom.
      I'd thought of sticking with an all-horizontal bolt system, and
      putting the chine bolts in little floodable compartments outside
      the main watertight envelopes of the bow and stern (but recessed
      inside, and accessed by ports) or fastened into a chine runner,
      but the forward end of the ballast tank is a bit too thin to
      make that plan work, and moving it aft far enough to make it
      thicker would involve moving a bulkhead that really needs to
      stay where it is.

      The solution that I think I've found is to cut the ballast tank
      in half, and make it a permanent part of the bow and stern. Pairs
      of bolts and brackets, as used on the sheer of the original design,
      can be used to bolt the ends of the two ballast tanks together.
      The cockpit seat boxes can then be bolted on top of the two
      tanks (possibly with bolts that run all the way through solid
      beams to the bottom), and to the original brackets at the sheer.

      The neat thing about this is that for trailering, the cockpit seat
      bins can sit sideways on top of the ballast tank halves, which
      eliminates one entire trip, or lets you trailer her in one trip
      with two vehicles. Clever placement of the bolts might even let
      the seats bolt in securely using the same holes.

      Slamming into the face of a wave while the stern is still surfing
      down the previous one will put a heavy tension load on the bolts
      holding the ballast tanks together, a lighter load on the bolts
      holding the cockpit seats on the ballast tanks, and a heavy
      compression load at the sheer; she ought to stand up to that.
      In the original design, the same scenario results in a very heavy
      shearing load on the little skegs holding the tank ends in, and
      a torsion load on the bolts at the sheer. If she hits hard
      enough (or fatigue sets in enough) that a skeg parts or a tank
      end slips out, you wind up with a sloop and a catboat, or a
      sloop, a powerboat, and a raft....

      -- Sue --
      (all of the above will make more sense when accompanied by sketches)

      --
      Susan Davis <futabachan@...>
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