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Re: water ballast vs lead, iron, etc

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  • Guy Vandegrift
    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
    Message 1 of 25 , Dec 1, 2006
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      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.

      Regarding your second comment, we didn't add the fishing weights, but
      shifted them "leeward" from the "windward" side. There was no "wind"
      of course, and the actual force of the sails on the boat are
      complicated and dynamic. Though unable to model all complexities, I
      believe our experiment exactly matched what computer stability codes do.

      Enjoyed your commentary,

      Guy
    • 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 2 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 3 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 4 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 5 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 6 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 7 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 8 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 9 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 10 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 11 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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