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41341Re: Birdwatcher II - others being built?

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  • Bob Larkin
    Jan 1, 2005
      Nels wrote:
      >I am not certain if the hull is a TRUE ply/foam/ply sandwich
      >construction as the foam is not laminated to the plywood. Or is it? I
      >am not sure if it is meant to be a structural component. Of course
      >the doubled ply is really strong by itself - even without the foam!

      The installation of the foam presents several interesting issues. I have
      not seen Bolger address them specifically, but it strikes me as most
      desirable to make the foam and plywood into a sandwich, with strong
      adhesive. Structurally, this increases the strength for forces pulling from
      the outside, that may occur when the boat is heeled. Also important, is to
      prevent voids that can collect water. I was planning to use some 2-part
      expanding foam in small left-over volumes around the foam sheets.

      I have used the expanding foam before, and I remember problems in
      controlling the stuff! It sometimes didn't want to go where you wanted,
      and other times wanted to sneak out through cracks. I want to have all the
      expanding foam in place before putting the inner plywood on. This allows
      cleanup and redo of missed areas. The expanding foam I used also required
      good ventilation! Maybe they have better products now, as this was 15
      years ago.

      John K., I plan to do some small test panels with the foam sandwich. I can
      drop off a sample for you to play with if you want? This will probably be
      early Feb. You will probably think of good ways to torture the stuff.

      >If I was
      >to use 3/8" MDO I would only glass below the waterline. If I used
      >1/4" I would glass the entire exterior. The weight would probably end
      >up the same. Of course it also depends on what kind of plywood one

      Nels, on the build up for the sides, I now understand the constraints that
      David was working with! Thanks. I agree on the use of glass for the 1/4"
      plywood, but it probably could be thinner than the bottom.

      >A great asset of the design is it's 6" draft and low momemntum which
      >means it will pass right over most obstructions or just bounce off
      >with nary more than a scratch. All blows will be glancing with the
      >exception of the bottom and chimes and these are easily reinforced
      >with extra glass taping, or even a sacrificial skid.
      >How about UMHD strakes like Bruce used on Rose?

      Yes, and it sounds like another good area to learn more about. I have used
      it for small sliding parts---but why not the boat. BTW, I plan to take the
      boat all the way to the water on the trailer ;-)

      I am really curious about the slot closure system. Can you elaborate
      on that?

      Bolger does not overburden us with details for the hard hatches. Made up in
      four overlapping sections, they are again fabricated from a sandwich of
      1-inch foam with 3mm plywood top and bottom. The aft section has a 32-inch
      cover that hinges forward. They sit just high enough over the
      standing-room comings to allow drainage between sections. There are no
      suggestions for stowage. As drawn, they are too long to fit in the forward

      These hatches are somewhat large, typically 2x4 feet. I will try to report
      later on their apparent ability to bear weight. Again this is the sandwich
      question. They also are easy to modify/replace, if needed.

      My present plan is to build this type of hatch for the forward and aft
      compartments and start out with a minimal soft cover for the middle (plus a
      middle tent for camping). I'm still looking for proper latches.

      Many thanks to all for the fine comments!

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