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Re: water ballast vs. lead, iron, etc

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  • graeme19121984
    The more I ve pondered some emblematic examples of the extraordinarily parsimonious writing style of PCB the younger, the more I wonder at the wonder of it.
    Message 1 of 25 , Dec 1, 2006
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      The more I've pondered some emblematic examples of the
      extraordinarily parsimonious writing style of PCB the younger, the
      more I wonder at the wonder of it. The vision exchanged, much said
      in little ink.

      There's the old adage of a picture being worth a thousand words
      (here too PCB excels). Ho hum, heard that before. However I find it
      remarkable how sometimes PCB has strikingly used but a few words to
      describe a thousand pictures.

      For example, regarding the current discussion, I believe all to do
      with ballast, cross sectional shape, beam, draft, length,
      metacentric height, COG, COB, GZ, deep bulb keels, though perhaps
      not specifically ballast moment of inertia, was REDUCED to writing
      by PCB the younger quite some time ago. One needs perhaps be a
      little familiar with the context where presented, and no doubt a
      rudimentary understanding of the naval design terms also helps, but
      once assimilated I think a reasonable approximation of almost how
      any hull is likely to perform under press of sail can be "seen" in
      the mind's eye when guided by PCB's enlightening insight, so well
      expressed.

      PCB could explain it in two sentences. I have to repeat that, in
      two (!!) sentences:

      "The upright stance is possible because in spite of being narrow for
      her length, she's wide for her depth under water." (FS, p81 Rondo
      ll); and

      "But regardless of her length, a boat that is deep-bodied
      for her breadth, and doesn't carry her ballast on a deep fin, will
      be tender under sail." (FS, p69 Blackgauntlet ll)

      This explanation takes quite a bit of unpacking, however I believe
      it contains all that is required - perhaps a book or two's worth.

      (Also, when mentally considering neutral ballast hull volumes simply
      subtract them from the overall hull shape until they are above the
      waterline.)

      Graeme
    • Mike French
      When the Shearwater (larger Dovkie)was designed I believe PCB and Peter Duff thought about water ballast. They decided on lead approx 2 inches thick, glassed
      Message 2 of 25 , Dec 1, 2006
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        When the Shearwater (larger Dovkie)was designed I believe PCB and
        Peter Duff thought about water ballast. They decided on lead approx 2
        inches thick, glassed to the inside of the flat hull bottom, across to
        the beginning of the turn of the bilge on each side and 2 feet or so
        fore and aft. It was located at the bottom of the companionway and did
        not interfere much. It added inertia, but good righting moment only
        when well heeled. It represented about 500 lbs out of a total of 2200
        lbs - which is still pretty light for a 28 footer.
      • 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 3 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 4 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 5 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 6 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 7 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 8 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 9 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 10 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 11 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 12 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 13 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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