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Re: water ballast vs lead, iron, etc

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  • 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 1 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 2 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 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
          • 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 5 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 6 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 7 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 8 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 9 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 10 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 11 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 12 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 13 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 14 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 15 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 16 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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