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Re: water ballast vs lead, iron, etc

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  • Patric Albutat
    Since the dreaded stability question has been raised again, here s a link I came about (after the last discussion ended in a fierce battle over multihulls -
    Message 1 of 25 , Dec 1, 2006
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      Since the dreaded 'stability question' has been raised again, here's a
      link I came about (after the last discussion ended in a fierce battle
      over multihulls - guess I'll have to pick my words more carefully):
      http://www.boatdesign.com/postings/pages/knockdown.htm
      If everybody knows already, sorry!

      My search for rightening moment actually reveiled not only that a flat
      boat without any keel at all can still be a very seaworty vessel, it
      has been done for more than 3000 years:
      http://www.flickr.com/photos/67816918@N00/sets/72157594372244167

      As for internal ballast: the British Navy (Nelson's Navy that is) used
      shingle

      Patric
    • Guy Vandegrift
      Patric, No need to apologize about the Junk photos. I have long looked for something like this. And I forgive you for reposting the well known, but classic,
      Message 2 of 25 , Dec 1, 2006
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        Patric, No need to apologize about the Junk photos. I have long
        looked for something like this. And I forgive you for reposting the
        well known, but classic, link on Bolger Box knockdowns.

        Guy

        --- In bolger@yahoogroups.com, "Patric Albutat" <albutat@...> wrote:
        > http://www.boatdesign.com/postings/pages/knockdown.htm
        > If everybody knows already, sorry!
        >
        > My search for rightening moment actually reveiled not only that a flat
        > boat without any keel at all can still be a very seaworty vessel, it
        > has been done for more than 3000 years:
        > http://www.flickr.com/photos/67816918@N00/sets/72157594372244167
      • graeme19121984
        Guy, I m missing something here. How can the boat lift in static conditions when the mass is unchanged. Lift defined by displacing less water. How is the
        Message 3 of 25 , Dec 1, 2006
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          Guy,

          I'm missing something here. How can the boat lift in static
          conditions when the mass is unchanged. "Lift" defined by displacing
          less water. How is the boat made lighter?

          By the way, please keep on inquiring. Very interesting work.

          Graeme

          PS Sorry group for three repetitive posts above. Not sure how that
          happened - I hit stop after send, once, as I wanted to edit
          something.

          --- In bolger@yahoogroups.com, "Guy Vandegrift" <guy.vandegrift@...>
          wrote:
          >
          > Graeme,
          >
          > You are absolutly right in observing that the lifting of the boat
          > begins as soon as the angle deviates from zero. Hence, the linear
          > relation between torque and angle is never strictly true. I believe
          > (hope) that this effect is sufficiently small in most boats. This
          > needs to be checked, either numerically or experimentally.
        • Guy Vandegrift
          Ouch! You caught me being vague and sloppy in my language. When one chine goes down, the other one comes up. But in my defense, the center of the bottom does
          Message 4 of 25 , Dec 1, 2006
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            Ouch! You caught me being vague and sloppy in my language. When one
            chine goes down, the other one comes up. But in my defense, the
            center of the bottom does "lift" up.

            I developed this insight when I was building Michalak's 4'x12' Piccup
            Pram. I saw these 4'x8' Styrofoam slabs (maybe 3" thick) in a home
            improvement store and wondered how one would behave if it rested
            (empty) on water. By my stiffness formula, the empty slab would be
            very stiff, but only at very, very, small angle. Once the bottom
            lifted above the water, a slight breeze would flip it over.

            A typical Advanced Sharpie might resemble this slab. When I first
            started looking at boat hulls on the internet, I was surprized by the
            shallow draft.

            --- In bolger@yahoogroups.com, "graeme19121984" <graeme19121984@...>
            wrote:
            >
            > Guy,
            >
            > I'm missing something here. How can the boat lift in static
            > conditions when the mass is unchanged. "Lift" defined by displacing
            > less water. How is the boat made lighter?
            >
          • pvanderwaart
            ... You are quite right that the stiffness of a flat-bottomed hull disappears at quite small angles of heel. When Bolger did some after-capsize stability
            Message 5 of 25 , Dec 2, 2006
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              > By my stiffness formula, the empty slab would be
              > very stiff, but only at very, very, small angle. Once the bottom
              > lifted above the water, a slight breeze would flip it over.

              You are quite right that the stiffness of a flat-bottomed hull
              disappears at quite small angles of heel. When Bolger did some
              after-capsize stability studies of the Martha Jane sharpie, he found
              that the point of no return was much higher than expected, maybe 45 or
              50 degrees. AS-29 was not compromized by thoughts of trailering and is
              more heavily ballasted.

              High topsides and careful attention to hatches and other openings are
              required for safety. You can see this in production boats with inside
              ballast too, such as the water-ballasted 25-footers from Hunter and
              Catalina.

              Peter
            • Guy Vandegrift
              My boat stability project has reached the point where it must go dormant till I get collaborators. The price a professor pays for doing trivial research is
              Message 6 of 25 , Dec 2, 2006
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                My boat stability project has reached the point where it must go
                dormant till I get collaborators. The price a professor pays for doing
                "trivial" research is that it must focus on education. Anybody who can
                contribute is welcome to apply.

                I need someone who either did well in high school physics, geometry,
                and algebra, or who has strengthened these skills in college. Most
                college graduates have poor writing skills, but anybody who can
                write can be prinicpal author on a paper to AJP (American Journal of
                Physics). A high school student with a parent who can write, along
                with somebody who knows boats and can run hull stability software,
                would make an awesome team! Though most papers in AJP have one author,
                I think they will like the diversity and perhaps even physical
                remoteness of those who solve this problem.

                Guy

                See "Stiffness of an Advanced Sharpie" on my homepage at
                http://faculty.valpo.edu/gvandegr/.

                P.S. AJP pays authors ten times what I hear they pay contributors to
                MAIB, which is nothing.
              • Bob Slimak
                Hmmm..... ten times nothing is ... NOTHING! Bob ... Check out the all-new Yahoo! Mail beta - Fire up a more powerful email and get things done faster.
                Message 7 of 25 , Dec 4, 2006
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                  Hmmm..... ten times nothing is ... NOTHING!
                  Bob


                  ---------------------------------
                  Check out the all-new Yahoo! Mail beta - Fire up a more powerful email and get things done faster.

                  [Non-text portions of this message have been removed]
                • Guy Vandegrift
                  That s why I am not interested in writing the paper myself. Re: idea for overbuilt boat . I know I am mixing threads, but both are linked by my attempt to
                  Message 8 of 25 , Dec 5, 2006
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                    That's why I am not interested in writing the paper myself.

                    Re: "idea for overbuilt boat". I know I am mixing threads, but both
                    are linked by my attempt to collaborate via internet with a group of
                    kids, somewhere in the world. I think the LNS on that project is a
                    12-ft "overbuilt" dinghy out of 0.25in by 1.5in lathe sticks (the
                    cheaper the better). Instead of a double-transverse layer, consider
                    a cross-stitched "weave" of long transverse sticks with longitudinal
                    sticks only a few boardwidths accross (short to permit clamping).
                    That should solve the buckling problem.

                    They say the hull is only a third the cost of a boat. I bet if we
                    cut the cost of the hull by a third, people will find ways to cut the
                    other 2/3s by 1/3. Both projects are long-range and admittedly long-
                    shots, justified by the idea that this is educational, and not too
                    dangerous if the work is done by WELL SUPERVISED middle or high
                    school kids. This is more fun and a lot more usefull than most of
                    the stuff I wrote for AJP.

                    Guy


                    --- In bolger@yahoogroups.com, Bob Slimak <otter55806@...> wrote:
                    >
                    > Hmmm..... ten times nothing is ... NOTHING!
                    > Bob
                  • derbyrm
                    Careful on the lath. The stuff one bought forty years ago was fine wood; continuous lengths with few flaws. I used it for model RR roadbed. A few years
                    Message 9 of 25 , Dec 5, 2006
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                      Careful on the lath. The stuff one bought forty years ago was fine wood; continuous lengths with few flaws. I used it for model RR roadbed. A few years later the only sticks I could find were made up from short segments joined with finger splices. It didn't bend and it broke if you looked at it funny. Probably still adequate for rose vines, but worthless for the task I wanted.

                      As for collaboration, don't you first have to find someone who is as enthusiastic about the idea as you are?

                      Roger
                      derbyrm@...
                      http://home.insightbb.com/~derbyrm

                      ----- Original Message -----
                      From: Guy Vandegrift
                      To: bolger@yahoogroups.com
                      Sent: Tuesday, December 05, 2006 11:40 AM
                      Subject: [bolger] Re: water ballast vs lead, iron, etc


                      That's why I am not interested in writing the paper myself.

                      Re: "idea for overbuilt boat". I know I am mixing threads, but both
                      are linked by my attempt to collaborate via internet with a group of
                      kids, somewhere in the world. I think the LNS on that project is a
                      12-ft "overbuilt" dinghy out of 0.25in by 1.5in lathe sticks (the
                      cheaper the better). Instead of a double-transverse layer, consider
                      a cross-stitched "weave" of long transverse sticks with longitudinal
                      sticks only a few boardwidths accross (short to permit clamping).
                      That should solve the buckling problem.

                      They say the hull is only a third the cost of a boat. I bet if we
                      cut the cost of the hull by a third, people will find ways to cut the
                      other 2/3s by 1/3. Both projects are long-range and admittedly long-
                      shots, justified by the idea that this is educational, and not too
                      dangerous if the work is done by WELL SUPERVISED middle or high
                      school kids. This is more fun and a lot more usefull than most of
                      the stuff I wrote for AJP.

                      Guy

                      --- In bolger@yahoogroups.com, Bob Slimak <otter55806@...> wrote:
                      >
                      > Hmmm..... ten times nothing is ... NOTHING!
                      > Bob





                      [Non-text portions of this message have been removed]
                    • Guy Vandegrift
                      Thanks for warning me about lathe. I would want to do any scarfing myself. Regarding the enthusiasm problem, middle school kids can get enthused about
                      Message 10 of 25 , Dec 5, 2006
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                        Thanks for warning me about lathe. I would want to do any scarfing
                        myself. Regarding the enthusiasm problem, middle school kids can get
                        enthused about anything. I just have to verify that the middle school
                        is aware of the safety issues. Also, a novice amateur boatbuilder
                        might like the idea of an overbuilt dinghy. I didn't regret
                        overbuilding my Piccup Pram until I tried to lift it. Guy.

                        --- In bolger@yahoogroups.com, "derbyrm" <derbyrm@...> wrote:
                        >
                        > Careful on the lath. ...
                        > ... don't you first have to find someone who is as enthusiastic
                        about the idea as you are?
                        >
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