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

Re: water ballast revisited

Expand Messages
  • Chuck Leinweber
    John: This is an excellent visualization! Everybody: Read this! I don t think that you can reduce the water ballast question to math anyway. You have
    Message 1 of 9 , Feb 29, 2000
    • 0 Attachment
      John:

      This is an excellent visualization! Everybody: Read this! I don't think
      that you can reduce the water ballast question to math anyway. You have
      succeeded in putting the whole thing in a nutshell. Thanks.

      Chuck Leinweber
      Duckworks Magazine
      http://www.duckworksmagazine.com


      ----- Original Message -----
      From: John Paul Bullen <drjpbullen@...>
      To: <boatdesign@onelist.com>
      Sent: Wednesday, March 01, 2000 8:20 AM
      Subject: [boatdesign] water ballast revisited


      > From: John Paul Bullen <drjpbullen@...>
      >
      > Hi all,
      > Sorry to revisit this subject while everyone has moved to a higher plane,
      but
      > I am a "bear of little brain" and it took a while to think it through.I
      > provide this for the benefit of people like myself who get cold sweats and
      an
      > attack of the vapours when they see a mathematical formula.
      > Unfortunately, without maths the talk is longwinded, sorry.
      >
      > A couple of weeks ago someone wrote that water ballast only works when
      above
      > the water level. I suggest the following "thought experiment" to
      demonstrate
      > that this need not always be the case.
      >
      > Imagine a length of pipe with the ends blanked off to represent the hull.
      > Chuck it in the water and it floats. Adjust the density of the wall of the
      > pipe so that it floats mostly submerged. (It has no top or bottom side in
      this
      > condition as the centre of gravity and the centre of bouyancy are along
      the
      > centre of the long axis of the pipe) Now glue a small sachet of water
      inside
      > the pipe. It will now float mostly submerged, but with the sachet of water
      at
      > the bottom, and below water level. Interesting!!
      >
      > Now, to complete the mind game, remove the sachet of water, and this time
      > glue it onto the outside of the pipe. Intuitively, in this condition the
      water
      > will only exert a righting effect when it is lifted above water level.
      Even
      > more interesting!
      >
      > How does one explain this, and what does it mean for boat design?
      > I'm no expert on any of this stuff, but two things that need to be
      remembered
      > are:
      > 1)that water ballast can be used to move (lower) the centre of gravity of
      a
      > hull
      > 2)that the relationship of the C of G compared to the C of B is what
      provides
      > the righting effect of the ballast
      > 3)most hulls take a shape more like a somewhat squashed pipe, and when
      this
      > flattened shape starts to heal the centre of bouyancy shifts to the
      leeward
      > side increasing the righting effect. The extreme example of this is the
      > catamaran when it lifts a hull the centre of bouyancy shifts to somewhere
      in
      > the hull that remains in the water.
      >
      > hope this helps, JohnPaul
      >
      >
      >
      > ____________________________________________________________________
      > Get your own FREE, personal Netscape WebMail account today at
      http://webmail.netscape.com
      >
      > ------------------------------------------------------------------------
      > Get a FREE $15 BN.com gift certificate when you join carclub.com.
      > As a member, you can save up to $550 a year if you own a car, and
      > thousands more when you're buying one.
      > http://click.egroups.com/1/1945/1/_/446985/_/951861037/
      > ------------------------------------------------------------------------
      >
      >
    • KSzafran/LClayman
      ... Yes. Yes, yes, yes, yes, yes. Yes.
      Message 2 of 9 , Feb 29, 2000
      • 0 Attachment
        Chuck Leinweber wrote:
        >
        > From: "Chuck Leinweber" <chuck@...>
        >
        > John:
        >
        > This is an excellent visualization! Everybody: Read this! I don't think
        > that you can reduce the water ballast question to math anyway. You have
        > succeeded in putting the whole thing in a nutshell. Thanks.
        >

        Yes.

        Yes, yes, yes, yes, yes.

        Yes.

        > Chuck Leinweber
        > Duckworks Magazine
        > http://www.duckworksmagazine.com
        >
        > ----- Original Message -----
        > From: John Paul Bullen <drjpbullen@...>
        > To: <boatdesign@onelist.com>
        > Sent: Wednesday, March 01, 2000 8:20 AM
        > Subject: [boatdesign] water ballast revisited
        >
        > > From: John Paul Bullen <drjpbullen@...>
        > >
        > > Hi all,
        > > Sorry to revisit this subject while everyone has moved to a higher plane,
        > but
        > > I am a "bear of little brain" and it took a while to think it through.I
        > > provide this for the benefit of people like myself who get cold sweats and
        > an
        > > attack of the vapours when they see a mathematical formula.
        > > Unfortunately, without maths the talk is longwinded, sorry.
        > >
        > > A couple of weeks ago someone wrote that water ballast only works when
        > above
        > > the water level. I suggest the following "thought experiment" to
        > demonstrate
        > > that this need not always be the case.
        > >
        > > Imagine a length of pipe with the ends blanked off to represent the hull.
        > > Chuck it in the water and it floats. Adjust the density of the wall of the
        > > pipe so that it floats mostly submerged. (It has no top or bottom side in
        > this
        > > condition as the centre of gravity and the centre of bouyancy are along
        > the
        > > centre of the long axis of the pipe) Now glue a small sachet of water
        > inside
        > > the pipe. It will now float mostly submerged, but with the sachet of water
        > at
        > > the bottom, and below water level. Interesting!!
        > >
        > > Now, to complete the mind game, remove the sachet of water, and this time
        > > glue it onto the outside of the pipe. Intuitively, in this condition the
        > water
        > > will only exert a righting effect when it is lifted above water level.
        > Even
        > > more interesting!
        > >
        > > How does one explain this, and what does it mean for boat design?
        > > I'm no expert on any of this stuff, but two things that need to be
        > remembered
        > > are:
        > > 1)that water ballast can be used to move (lower) the centre of gravity of
        > a
        > > hull
        > > 2)that the relationship of the C of G compared to the C of B is what
        > provides
        > > the righting effect of the ballast
        > > 3)most hulls take a shape more like a somewhat squashed pipe, and when
        > this
        > > flattened shape starts to heal the centre of bouyancy shifts to the
        > leeward
        > > side increasing the righting effect. The extreme example of this is the
        > > catamaran when it lifts a hull the centre of bouyancy shifts to somewhere
        > in
        > > the hull that remains in the water.
        > >
        > > hope this helps, JohnPaul
        > >
        > >
        > >
        > > ____________________________________________________________________
        > > Get your own FREE, personal Netscape WebMail account today at
        > http://webmail.netscape.com
        > >
        > > ------------------------------------------------------------------------
        > > Get a FREE $15 BN.com gift certificate when you join carclub.com.
        > > As a member, you can save up to $550 a year if you own a car, and
        > > thousands more when you're buying one.
        > > http://click.egroups.com/1/1945/1/_/446985/_/951861037/
        > > ------------------------------------------------------------------------
        > >
        > >
        >
        > ------------------------------------------------------------------------
        > Shabang!com is the place to get your FREE eStore, Absolutely FREE
        > Forever. If you have any desires to sell your products or services
        > online, or you want to expand your customer base for FREE, Come check
        > out Shabang!com FREE eStores!
        > http://click.egroups.com/1/1299/1/_/446985/_/951868935/
        > ------------------------------------------------------------------------
      • John Paul Bullen
        Hi all, Sorry to revisit this subject while everyone has moved to a higher plane, but I am a bear of little brain and it took a while to think it through.I
        Message 3 of 9 , Mar 1 6:20 AM
        • 0 Attachment
          Hi all,
          Sorry to revisit this subject while everyone has moved to a higher plane, but
          I am a "bear of little brain" and it took a while to think it through.I
          provide this for the benefit of people like myself who get cold sweats and an
          attack of the vapours when they see a mathematical formula.
          Unfortunately, without maths the talk is longwinded, sorry.

          A couple of weeks ago someone wrote that water ballast only works when above
          the water level. I suggest the following "thought experiment" to demonstrate
          that this need not always be the case.

          Imagine a length of pipe with the ends blanked off to represent the hull.
          Chuck it in the water and it floats. Adjust the density of the wall of the
          pipe so that it floats mostly submerged. (It has no top or bottom side in this
          condition as the centre of gravity and the centre of bouyancy are along the
          centre of the long axis of the pipe) Now glue a small sachet of water inside
          the pipe. It will now float mostly submerged, but with the sachet of water at
          the bottom, and below water level. Interesting!!

          Now, to complete the mind game, remove the sachet of water, and this time
          glue it onto the outside of the pipe. Intuitively, in this condition the water
          will only exert a righting effect when it is lifted above water level. Even
          more interesting!

          How does one explain this, and what does it mean for boat design?
          I'm no expert on any of this stuff, but two things that need to be remembered
          are:
          1)that water ballast can be used to move (lower) the centre of gravity of a
          hull
          2)that the relationship of the C of G compared to the C of B is what provides
          the righting effect of the ballast
          3)most hulls take a shape more like a somewhat squashed pipe, and when this
          flattened shape starts to heal the centre of bouyancy shifts to the leeward
          side increasing the righting effect. The extreme example of this is the
          catamaran when it lifts a hull the centre of bouyancy shifts to somewhere in
          the hull that remains in the water.

          hope this helps, JohnPaul



          ____________________________________________________________________
          Get your own FREE, personal Netscape WebMail account today at http://webmail.netscape.com
        • Peter & Polly Vanderwaart
          Good example. Now the quiz: suppose that your thick-walled tube has a gouge on the outside - just a depression, not a hole. No water sachet. Which way will the
          Message 4 of 9 , Mar 2 6:10 AM
          • 0 Attachment
            Good example.

            Now the quiz: suppose that your thick-walled tube has a gouge on the
            outside - just a depression, not a hole. No water sachet. Which way
            will the tube float?

            Peter
          • Peter & Polly Vanderwaart
            Good example. Now the quiz: suppose that your thick-walled tube has one side shaved flat on the outside. No water sachet. Which way will the tube float? Peter
            Message 5 of 9 , Mar 2 6:56 AM
            • 0 Attachment
              Good example.

              Now the quiz: suppose that your thick-walled tube has one side shaved
              flat on the outside. No water sachet. Which way will the tube float?

              Peter
            • Lew Clayman
              Shaved side up, it s lighter. I saved a glass har from the recycling last night, maybe I ll get my kids together and do a science fair project this weekend.
              Message 6 of 9 , Mar 2 7:18 AM
              • 0 Attachment
                Shaved side up, it's lighter.

                I saved a glass har from the recycling last night, maybe I'll get my kids
                together and do a science fair project this weekend. Report to follow.
                However I do not plan to shave the glass.

                --- Peter & Polly Vanderwaart <pvanderw@...> wrote:
                > From: "Peter & Polly Vanderwaart" <pvanderw@...>
                >
                > Good example.
                >
                > Now the quiz: suppose that your thick-walled tube has one side shaved
                > flat on the outside. No water sachet. Which way will the tube float?
                >
                > Peter
                >
                >
                > ------------------------------------------------------------------------
                > GET A NEXTCARD VISA, in 30 seconds! Get rates
                > as low as 0.0% Intro APR and no hidden fees.
                > Apply NOW!
                > http://click.egroups.com/1/975/1/_/446985/_/952009009/
                > ------------------------------------------------------------------------
                >
                >
                >
                >

                =====
                All of your prayers are answered, but sometimes the answer is no.
                - George Burns as God, in the movie Oh God II
                =====
                __________________________________________________
                Do You Yahoo!?
                Talk to your friends online with Yahoo! Messenger.
                http://im.yahoo.com
              • David Beede
                Wouldn t it float flat side up? The C of G being moved towards the round side? However the gouged one stumps me. Seems the surface area of the tube would
                Message 7 of 9 , Mar 2 7:20 AM
                • 0 Attachment
                  Wouldn't it float flat side up? The C of G being moved towards the round
                  side?
                  However the gouged one stumps me. Seems the surface area of the tube would
                  increase so the tupe material would weigh more, however it would now
                  displace less water? Hmm... float lower in the water with the gouge down?
                  That's my guess.
                  djb

                  Peter & Polly Vanderwaart wrote:

                  > From: "Peter & Polly Vanderwaart" <pvanderw@...>
                  >
                  > Good example.
                  >
                  > Now the quiz: suppose that your thick-walled tube has one side shaved
                  > flat on the outside. No water sachet. Which way will the tube float?
                  >
                  > Peter
                  >
                  > ------------------------------------------------------------------------
                  > GET A NEXTCARD VISA, in 30 seconds! Get rates
                  > as low as 0.0% Intro APR and no hidden fees.
                  > Apply NOW!
                  > http://click.egroups.com/1/975/1/_/446985/_/952009009/
                  > ------------------------------------------------------------------------

                  --

                  SOME CLICKS THAT COUNT!!
                  Feed someone.
                  http://www.thehungersite.com/
                  Save a little rain forest.
                  http://rainforest.care2.com/front.html/player12296

                  Simplicity Boats (& mirror sites)
                  http://members.tripod.com/simplicityboats/index.html
                  http://members.xoom.com/simpleboats/index.html
                  Here's my latest boat:
                  http://members.tripod.com/simplicityboats/featherwind.html
                  http://members.xoom.com/simpleboats/featherwind.html
                  Quasi esoteric musical instruments
                  http://unicornstrings.com
                • David Beede
                  Wouldn t it float flat side up? The C of G being moved towards the round side? However the gouged one stumps me a bit. Seems the surface area of the tube would
                  Message 8 of 9 , Mar 2 7:21 AM
                  • 0 Attachment
                    Wouldn't it float flat side up? The C of G being moved towards the round
                    side?
                    However the gouged one stumps me a bit. Seems the surface area of the tube
                    would increase so the tube material would weigh more, however it would now
                    displace less water? Hmm... float lower in the water with the gouge down?
                    That's my guess.
                    djb

                    Peter & Polly Vanderwaart wrote:

                    > From: "Peter & Polly Vanderwaart" <pvanderw@...>
                    >
                    > Good example.
                    >
                    > Now the quiz: suppose that your thick-walled tube has one side shaved
                    > flat on the outside. No water sachet. Which way will the tube float?
                    >
                    > Peter
                    >
                    > ------------------------------------------------------------------------
                    > GET A NEXTCARD VISA, in 30 seconds! Get rates
                    > as low as 0.0% Intro APR and no hidden fees.
                    > Apply NOW!
                    > http://click.egroups.com/1/975/1/_/446985/_/952009009/
                    > ------------------------------------------------------------------------

                    --

                    SOME CLICKS THAT COUNT!!
                    Feed someone.
                    http://www.thehungersite.com/
                    Save a little rain forest.
                    http://rainforest.care2.com/front.html/player12296

                    Simplicity Boats (& mirror sites)
                    http://members.tripod.com/simplicityboats/index.html
                    http://members.xoom.com/simpleboats/index.html
                    Here's my latest boat:
                    http://members.tripod.com/simplicityboats/featherwind.html
                    http://members.xoom.com/simpleboats/featherwind.html
                    Quasi esoteric musical instruments
                    http://unicornstrings.com
                  • David Beede
                    Peter, I sent the thought experiment to Jim Michalak for his take on it. Here tis. ... I agree with the comments. It took me a while to figure out because I
                    Message 9 of 9 , Mar 2 7:24 AM
                    • 0 Attachment
                      Peter,
                      I sent the thought experiment to Jim Michalak for his take on it. Here
                      'tis.

                      > Jim,
                      > This is from a discussion on the boat design list. I found your
                      > article and graphs on ballast interesting, and I'd love any comments a
                      > real engineer might add to this water ballast thought experiment.
                      > Thanks,
                      > David

                      I agree with the comments. It took me a while to figure out because I
                      had also seen so many times that only the water ballast above the
                      waterline counts. That is true only if a tank is added to the outside of
                      the normal hull. In that case the tank has neutral weight because the
                      added ballast is exactly balanced by the buoyancy water that tank
                      displaces, until the tank is lifted out of the water, of course.

                      If the tank is internal to the normal hull then that is not usually
                      true. The ballast is just weight and could be any material with the same
                      weight and cg location, the boat has no way of knowing if the tank has
                      water or sand or concrete or lead inside. The added weight is still
                      balanced by an equal amount of displaced water but now the diplacement
                      is spread out over the normal hull.

                      JIm



                      Peter & Polly Vanderwaart wrote:

                      > From: "Peter & Polly Vanderwaart" <pvanderw@...>
                      >
                      > Good example.
                      >
                      > Now the quiz: suppose that your thick-walled tube has one side shaved
                      > flat on the outside. No water sachet. Which way will the tube float?
                      >
                      > Peter
                      >
                      > ------------------------------------------------------------------------
                      > GET A NEXTCARD VISA, in 30 seconds! Get rates
                      > as low as 0.0% Intro APR and no hidden fees.
                      > Apply NOW!
                      > http://click.egroups.com/1/975/1/_/446985/_/952009009/
                      > ------------------------------------------------------------------------

                      --

                      SOME CLICKS THAT COUNT!!
                      Feed someone.
                      http://www.thehungersite.com/
                      Save a little rain forest.
                      http://rainforest.care2.com/front.html/player12296

                      Simplicity Boats (& mirror sites)
                      http://members.tripod.com/simplicityboats/index.html
                      http://members.xoom.com/simpleboats/index.html
                      Here's my latest boat:
                      http://members.tripod.com/simplicityboats/featherwind.html
                      http://members.xoom.com/simpleboats/featherwind.html
                      Quasi esoteric musical instruments
                      http://unicornstrings.com
                    Your message has been successfully submitted and would be delivered to recipients shortly.