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Re: water ballast vs lead, iron, etc

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  • graeme19121984
    Guy, at your The Stiffness of an Advanced Sharpie at http://faculty.valpo.edu/gvandegr/ there is this: This axis of rotation ensures that the total area
    Message 1 of 25 , Dec 1, 2006
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      Guy,

      at your "The Stiffness of an Advanced Sharpie" at
      http://faculty.valpo.edu/gvandegr/ there is this:


      "This axis of rotation ensures that the total area of this
      underwater section remains constant. Close inspection of the graph
      indicates that the rotation slightly increases the area under the
      waterline. Hence the rotation is accompanied by a slight lifting of
      the boat, which becomes important only at large angle, I believe."

      What lifts the boat? How is it lifted if it remains the same mass?
      (disregarding any lifting component of the forces on any sail)

      I can imagine wider hull sections aft coming into play as they are
      immersed (more) with increasing heel, and so perhaps lifting this
      represented midships cross section. If this is the case then the
      data set gained from only this representative cross section would be
      insufficient to construct a generally representative model.

      If this is not the case it would appear that, as the boat is not
      able to just arbitrarily "lift" by some unknown means, then the
      assumptions made from this represented cross section are somewhat
      erroneous and therefore any further calculations based on them are
      also going to be in error. My calculus skills are too rusty to
      comment on your derived equations, and the insights and intuitions
      gained, other than to raise the point that any initial error in
      assumptions may be compounded, perhaps more than trivially so.


      Graeme
    • graeme19121984
      I meant to observe first that if there is increased area under the waterline at this cross section then that at first would appear to indicate more water being
      Message 2 of 25 , Dec 1, 2006
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        I meant to observe first that if there is increased area under the
        waterline at this cross section then that at first would appear to
        indicate more water being displaced. If more water is displaced then
        the boat is being sunk not lifted as stated.

        Sail heeling forces may account for the boat being pressed into the
        water, and so the increased displacement. However the experiment
        involved heeling the boat by shifting fishing weights athwartships
        without dynamic sail forces, and so there seems need to explain how
        the extra water came to be displaced when the total mass of the boat
        remained constant.

        Graeme

        --- In bolger@yahoogroups.com, "graeme19121984" <graeme19121984@...>
        wrote:
        >
        > Guy,
        >
        > at your "The Stiffness of an Advanced Sharpie" at
        > http://faculty.valpo.edu/gvandegr/ there is this:
        >
        >
        > "This axis of rotation ensures that the total area of this
        > underwater section remains constant. Close inspection of the
        graph
        > indicates that the rotation slightly increases the area under the
        > waterline. Hence the rotation is accompanied by a slight lifting
        of
        > the boat, which becomes important only at large angle, I believe."
        >
        > What lifts the boat? How is it lifted if it remains the same mass?
        > (disregarding any lifting component of the forces on any sail)
        >
        > I can imagine wider hull sections aft coming into play as they are
        > immersed (more) with increasing heel, and so perhaps lifting this
        > represented midships cross section. If this is the case then the
        > data set gained from only this representative cross section would
        be
        > insufficient to construct a generally representative model.
        >
        > If this is not the case it would appear that, as the boat is not
        > able to just arbitrarily "lift" by some unknown means, then the
        > assumptions made from this represented cross section are somewhat
        > erroneous and therefore any further calculations based on them are
        > also going to be in error. My calculus skills are too rusty to
        > comment on your derived equations, and the insights and intuitions
        > gained, other than to raise the point that any initial error in
        > assumptions may be compounded, perhaps more than trivially so.
        >
        >
        > Graeme
        >
      • 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 3 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
        • 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 4 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
          • 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 5 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 6 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 7 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 8 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 9 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 10 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 11 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 12 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 13 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 14 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 15 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 16 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 17 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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