Loading ...
Sorry, an error occurred while loading the content.

Re: water ballast vs. lead, iron, etc

Expand Messages
  • 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
    View Source
    • 0 Attachment
      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 2 of 25 , Dec 1, 2006
      View Source
      • 0 Attachment
        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
        View Source
        • 0 Attachment
          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 4 of 25 , Dec 1, 2006
          View Source
          • 0 Attachment
            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 5 of 25 , Dec 1, 2006
            View Source
            • 0 Attachment
              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 6 of 25 , Dec 1, 2006
              View Source
              • 0 Attachment
                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 7 of 25 , Dec 1, 2006
                View Source
                • 0 Attachment
                  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 8 of 25 , Dec 1, 2006
                  View Source
                  • 0 Attachment
                    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 9 of 25 , Dec 1, 2006
                    View Source
                    • 0 Attachment
                      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 10 of 25 , Dec 2, 2006
                      View Source
                      • 0 Attachment
                        > 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 11 of 25 , Dec 2, 2006
                        View Source
                        • 0 Attachment
                          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 12 of 25 , Dec 4, 2006
                          View Source
                          • 0 Attachment
                            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 13 of 25 , Dec 5, 2006
                            View Source
                            • 0 Attachment
                              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 14 of 25 , Dec 5, 2006
                              View Source
                              • 0 Attachment
                                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 15 of 25 , Dec 5, 2006
                                View Source
                                • 0 Attachment
                                  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?
                                  >
                                Your message has been successfully submitted and would be delivered to recipients shortly.