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

water ballast vs lead, iron, etc

Expand Messages
  • timbo@wassons.org
    There are two things that determine righting moment of a sailboat. They are: Center of boyancy and Center of gravity The center of boyancy is determined by the
    Message 1 of 25 , Nov 28, 2006
    • 0 Attachment
      There are two things that determine righting moment of a sailboat.

      They are:
      Center of boyancy
      and
      Center of gravity

      The center of boyancy is determined by the shape of the portion of the
      hull that is currently displacing water.

      The center of gravity is determined by the location and weight of
      everything in the hull and the hull itself.

      When a boat is sitting dead in the water with no wave or wind action on
      it, if you were to take a cross section athwarships, the COB and the COG
      would be aligned in a vertical line.

      In a heavy displacement monohull (big lead keel), the COG is well below
      the COB. As the boat heels, the COG and the COB are no longer in the same
      vertical line, and this is what produces the righting moment on the boat.

      In a light monohull, (a bolger light schooner, perhaps?), the COG is above
      the COB. As the boat heels, the COB shifts a little bit due to the
      changing hull shape displacing water, and the COG is shifted by the crew
      moving to the rail. COG and COB no longer in a vertical line, thus
      producing a righting moment.

      In a catamaran, as the boat heels, the COB shifts radically as one hull
      displaces more water than the other. This large shift in COB for a small
      degree of heel is what gives cats their stiffness.

      So what of water ballast vs iron vs steel vs lead vs feather pillows?

      It simply comes down to where the COG is after adding the ballast. Lead
      in a keel produces the largest righting moment simply because it shifts
      the COG of the boat waaaaay down, without affecting the COB very much due
      to the increased displacement. This is also why bulb keels are better
      performing than a normal keel, because the COG shifts even farther down
      without affecting the COB any more than a normal keel.

      Water ballast is weight, just like any other type of weight. How
      effective it is comes down to where the COG and COB of the boat is after
      adding the ballast. Creating a water filled keel is silly and nobody
      does it, simply because it shifts the COB as much as it shifts the COG,
      making it pointless. It's even worse for feather pillows. As a keel
      shape, water ballast won't help with righting moment, but it will add
      mass, which may help with how the boat rides.

      There is also no need for water ballast (or any type of ballast for that
      matter) to be above the waterline to be effective. Ballast placed low in
      a craft tends to work better not because of the waterline or displacement,
      but simply because it lowers the COG more the lower it sits in the craft.

      Weight is weight. A ton of feathers is a ton, and a ton of lead is a ton.
      So why are feathers not used for ballast? Simply because the COG of the
      boat after loading it with a ton of feathers will likely be *higher*
      relative to the COB than it was before.

      Water ballast on both sides of a boat vs an equivalent amount on the
      centerline at the same height above the bottom will not help any more or
      less, because the COG is the same in both cases. As noted in the
      paragraph above, the placement of water ballast at the sides of the boat
      vs the centerline will increase the moment of inertia which means the boat
      won't rock as fast, but in terms of righting moment, they are identical.



      Bottom lines:
      Weight is weight.
      COG and COB determine righting moment.
      Dense materials tend to make more useful ballast because they provide a
      greater shift in the COG relative to the COB
    • adventures_in_astrophotography
      Timbo, ... Last night I did some calculations exactly along these lines and convinced myself that what I wrote yesterday was in error. I humbly withdraw those
      Message 2 of 25 , Nov 29, 2006
      • 0 Attachment
        Timbo,

        > Bottom lines:
        > Weight is weight.
        > COG and COB determine righting moment.
        > Dense materials tend to make more useful ballast because they provide
        > a greater shift in the COG relative to the COB

        Last night I did some calculations exactly along these lines and
        convinced myself that what I wrote yesterday was in error. I humbly
        withdraw those remarks! It's especially embarassing since I'm an
        astrodynamacist by trade and have enough physics and engineering
        background to know better. Next time I'll remember the old adage that
        a closed mouth gathers no foot.

        As for Cartoon 40, I still would use the lead shot, mainly for the
        reason given above, but also because it's simpler to build the boat
        that way, and another couple hundred pounds on the ramp shouldn't be a
        problem.

        Jon Kolb
        www.kolbsadventures.com/boatbuilding_index.htm
      • derbyrm
        But think of the pleasure you give to others. :-) Roger derbyrm@NOSPAMinsightbbNOSPAM.com http://home.insightbb.com/~derbyrm ... From:
        Message 3 of 25 , Nov 29, 2006
        • 0 Attachment
          But think of the pleasure you give to others. :-)

          Roger
          derbyrm@...
          http://home.insightbb.com/~derbyrm

          ----- Original Message -----
          From: adventures_in_astrophotography
          To: bolger@yahoogroups.com
          Sent: Wednesday, November 29, 2006 9:41 AM
          Subject: [bolger] Re: water ballast vs lead, iron, etc


          <snip>

          Next time I'll remember the old adage that a closed mouth gathers no foot.

          Jon Kolb
          www.kolbsadventures.com/boatbuilding_index.htm
          Recent Activity
          a.. 7New Members
          Visit Your Group
          SPONSORED LINKS
          a.. Bolger center
          b.. Bolger
          c.. Phil bolger
          Give Back
          Yahoo! for Good

          Get inspired

          by a good cause.

          Y! Toolbar
          Get it Free!

          easy 1-click access

          to your groups.

          Yahoo! Groups
          Start a group

          in 3 easy steps.

          Connect with others.
          .


          [Non-text portions of this message have been removed]
        • Christopher C. Wetherill
          Jon, Bear in mind that the two advantages of dense ballast are that it lowers the aggregate CG much more effectively than water, thereby giving a better
          Message 4 of 25 , Nov 29, 2006
          • 0 Attachment
            Jon,

            Bear in mind that the two advantages of dense ballast are that it lowers the
            aggregate CG much more effectively than water, thereby giving a better
            righting moment for a given displacement and that it provides righting
            moment in a swamped boat. The second point may be the source of this thread
            in the first place as PCB opined in one of his books that the water ballast
            in the design he was discussing at the time would not hold the boat upright
            for bailing when swamped.

            btw, we marine engineers have training in fluid dynamics, but I can't speak
            reliably about airplane flight dynamics without crunching numbers.

            V/R
            Chris
            -----Original Message-----
            From: bolger@yahoogroups.com [mailto:bolger@yahoogroups.com]On Behalf Of
            adventures_in_astrophotography
            Sent: Wednesday, November 29, 2006 9:41 AM
            To: bolger@yahoogroups.com
            Subject: [bolger] Re: water ballast vs lead, iron, etc


            Timbo,

            > Bottom lines:
            > Weight is weight.
            > COG and COB determine righting moment.
            > Dense materials tend to make more useful ballast because they provide
            > a greater shift in the COG relative to the COB

            Last night I did some calculations exactly along these lines and
            convinced myself that what I wrote yesterday was in error. I humbly
            withdraw those remarks! It's especially embarassing since I'm an
            astrodynamacist by trade and have enough physics and engineering
            background to know better. Next time I'll remember the old adage that
            a closed mouth gathers no foot.

            As for Cartoon 40, I still would use the lead shot, mainly for the
            reason given above, but also because it's simpler to build the boat
            that way, and another couple hundred pounds on the ramp shouldn't be a
            problem.

            Jon Kolb
            www.kolbsadventures.com/boatbuilding_index.htm
          • Nels
            ... I agree Jon, Somehow I have to wonder why a person would build a boat with a lot of effort and expense invested to keep water out and then put holes inside
            Message 5 of 25 , Nov 29, 2006
            • 0 Attachment
              --- In bolger@yahoogroups.com, "adventures_in_astrophotography"
              <jon@...> wrote:
              > As for Cartoon 40, I still would use the lead shot, mainly for the
              > reason given above, but also because it's simpler to build the boat
              > that way, and another couple hundred pounds on the ramp shouldn't be a
              > problem.
              >
              > Jon Kolb
              > www.kolbsadventures.com/boatbuilding_index.htm

              I agree Jon,

              Somehow I have to wonder why a person would build a boat with a lot of
              effort and expense invested to keep water out and then put holes
              inside to colect water to make it more stable. Not to mention the
              environmental issue regarding contamination of other waters with
              unfriendly flora and fauna.

              I would consider making the ballast boxes with closing lids and
              searching some garage sales for cast iron weights that are used in
              exercise machines. Many are also encapuslated with vinyl so they don't
              even rattle around.

              Transferring them back and forth to the boat would even give a person
              a work-out at the same time:-)

              Nels
            • Derek Waters
              ... I have to wonder why a person would build a boat ...to keep water out and then put holes inside to colect water to make it more stable. The primary
              Message 6 of 25 , Nov 29, 2006
              • 0 Attachment
                "... I have to wonder why a person would build a boat ...to keep water out
                and then put holes inside to colect water to make it more stable."

                The primary answer is, I think, that in the event of a hull breach all that
                metal ballast will tend to sink a wooden boat. The water ballasted hull will
                need much less volume devoted to floation to remain safely above water. Of
                course, the water ballast has a larger volume requirement than the metal,
                implying tradeoffs. The metal can sit with its mass concentrated lower in
                the same hull shape, but the foam has weight and generally needs to be
                placed high in the hull to ensure an upright tendency when flooded. In a
                converted design the high position of the foam is likely to reduce useful
                interior volume. Some shapes and sizes suit one approach, some another.

                'Horses for courses', in other words.

                cheers
                Derek
              • Nels
                ... all that ... hull will ... water. Of ... metal, ... lower in ... useful ... Good points. Perhaps a system to easily jettison the dumbells in case of a
                Message 7 of 25 , Nov 30, 2006
                • 0 Attachment
                  --- In bolger@yahoogroups.com, "Derek Waters" <dgw@...> wrote:
                  > The primary answer is, I think, that in the event of a hull breach
                  all that
                  > metal ballast will tend to sink a wooden boat. The water ballasted
                  hull will
                  > need much less volume devoted to floation to remain safely above
                  water. Of
                  > course, the water ballast has a larger volume requirement than the
                  metal,
                  > implying tradeoffs. The metal can sit with its mass concentrated
                  lower in
                  > the same hull shape, but the foam has weight and generally needs to be
                  > placed high in the hull to ensure an upright tendency when flooded. In a
                  > converted design the high position of the foam is likely to reduce
                  useful
                  > interior volume. Some shapes and sizes suit one approach, some another.
                  >
                  > 'Horses for courses', in other words.
                  >
                  > cheers
                  > Derek

                  Good points. Perhaps a system to easily jettison the dumbells in case
                  of a breach might be possible, and maybe quicker than pumping out
                  water tanks.

                  I wonder, in the olden days, if this is where the expression "getting
                  your rocks off" originated?

                  Nels
                • Guy Vandegrift
                  Timbo, As far as I can tell, your explanation of righting moment is correct. I think one can go a bit further when talking about a flat bottomed Bolger Box. I
                  Message 8 of 25 , Nov 30, 2006
                  • 0 Attachment
                    Timbo,

                    As far as I can tell, your explanation of righting moment is correct.
                    I think one can go a bit further when talking about a flat bottomed
                    Bolger Box. I finally documented some stuff I did with
                    non-mathematical students a few years ago. See the unfinished essay

                    "The Stiffness of an Advanced Sharpie" at

                    http://faculty.valpo.edu/gvandegr/

                    Though the equations take more time to work through, they can also
                    yield insights. For example, the blunt end of prams and advanced
                    sharpies only slightly increase the stiffness (small angle righting
                    moment) of a boat. But even a slight increase in overall beam has
                    significant effect.

                    If anybody has software to calculate righting moment, let me know.
                    There is more to done on this project.

                    Guy
                    --- In bolger@yahoogroups.com, timbo@... wrote:
                    >
                    > There are two things that determine righting moment of a sailboat.
                    >
                    > They are:
                    > Center of boyancy
                    > and
                    > Center of gravity
                    >
                  • 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 9 of 25 , Dec 1, 2006
                    • 0 Attachment
                      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 10 of 25 , Dec 1, 2006
                      • 0 Attachment
                        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 11 of 25 , Dec 1, 2006
                        • 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 12 of 25 , Dec 1, 2006
                          • 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 13 of 25 , Dec 1, 2006
                            • 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 14 of 25 , Dec 1, 2006
                              • 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 15 of 25 , Dec 1, 2006
                                • 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 16 of 25 , Dec 1, 2006
                                  • 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 17 of 25 , Dec 1, 2006
                                    • 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 18 of 25 , Dec 1, 2006
                                      • 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 19 of 25 , Dec 1, 2006
                                        • 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 20 of 25 , Dec 2, 2006
                                          • 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 21 of 25 , Dec 2, 2006
                                            • 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 22 of 25 , Dec 4, 2006
                                              • 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 23 of 25 , Dec 5, 2006
                                                • 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 24 of 25 , Dec 5, 2006
                                                  • 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 25 of 25 , Dec 5, 2006
                                                    • 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.