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Re: Model in relation to ballast

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  • donschultz8275
    ... design, does the ballast of that model relate in scale to the full scale version? ... I don t think it would scale in that direct linear fasion because the
    Message 1 of 13 , May 1, 2005
      --- In Michalak@yahoogroups.com, "Timtone" <tim@t...> wrote:
      > Can anyone tell me if when you build a scale model of a proposed
      design, does the ballast of that model relate in scale to the full
      scale version?
      >


      I don't think it would scale in that direct linear fasion because the
      capacity of the boat is increasing by a square factor. Michalak
      himself would be a better source, though Payson, who is a big
      proponent of model building may also have the answer.

      Michalak is the trained engineer, and Payson the "seat of the pants"
      guy.
    • Timtone
      ... I don t think it would scale in that direct linear fasion because the capacity of the boat is increasing by a square factor. Michalak himself would be a
      Message 2 of 13 , May 1, 2005
        >Thanks very much donshultz.

        I don't think it would scale in that direct linear fasion because the
        capacity of the boat is increasing by a square factor. Michalak
        himself would be a better source, though Payson, who is a big
        proponent of model building may also have the answer.

        Michalak is the trained engineer, and Payson the "seat of the pants"
        guy.





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      • Stefan Probst
        ... In theory (means I have no experience): The real boat would be 4 times as long, 4 times as broad, and 4 times as high, i.e. at the same WL it would
        Message 3 of 13 , May 1, 2005
          --- "Timtone" <tim@t...> wrote:
          > Can anyone tell me if when you build a scale model
          > of a proposed design, does the ballast of that model relate
          > in scale to the full scale version?
          >
          > In other words, if you did a 1/4 scale model of a 20 foot boat,
          > and found 100 pounds worked well as ballast.
          > Would this mean that 400 lbs. is going to work for the 20 footer?

          In theory (means I have no experience):
          The real boat would be 4 times as long, 4 times as broad, and 4 times
          as high, i.e. at the same WL it would displace 64 times as much water.

          Question is, whether your other weights (hull) are also to 1/4 scale:
          did you use ply that is 1/4 of the designed thickness?....

          So, in reality that 64 will not be exactly. And of course, waves don't
          scale up 1/4, but that is a totally different issue.

          Cheers,
          Stefan
        • Timtone
          Right. OK. I get you. Makes sense. It might be a little tricky scaling a 1/4 ply hull thickness down to 1/4 size. ~:0) But there may be some kind of factor
          Message 4 of 13 , May 1, 2005
            Right. OK. I get you. Makes sense.
            It might be a little tricky scaling a 1/4" ply hull thickness down to 1/4 size. ~:0)
            But there may be some kind of factor that would compensate for the 'natural' ballast of the boat...humans, gear batteries etc.
            I took donshultz's advice and went to the source for advice. I will share the result.

            Cheers, TT

            BTW.....Jim's newsletter essay on drawing and designing a hull is outstanding. I just came a cross it a few days ago. Finally, finding this info at a level my wee brain can comprehend. Eureka.

            ----- Original Message -----
            From: Stefan Probst
            To: Michalak@yahoogroups.com
            Sent: Sunday, May 01, 2005 07:56
            Subject: [Michalak] Re: Model in relation to ballast


            --- "Timtone" <tim@t...> wrote:
            > Can anyone tell me if when you build a scale model
            > of a proposed design, does the ballast of that model relate
            > in scale to the full scale version?
            >
            > In other words, if you did a 1/4 scale model of a 20 foot boat,
            > and found 100 pounds worked well as ballast.
            > Would this mean that 400 lbs. is going to work for the 20 footer?

            In theory (means I have no experience):
            The real boat would be 4 times as long, 4 times as broad, and 4 times
            as high, i.e. at the same WL it would displace 64 times as much water.

            Question is, whether your other weights (hull) are also to 1/4 scale:
            did you use ply that is 1/4 of the designed thickness?....

            So, in reality that 64 will not be exactly. And of course, waves don't
            scale up 1/4, but that is a totally different issue.

            Cheers,
            Stefan






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            [Non-text portions of this message have been removed]
          • Ronald Fossum
            1/4 x 1/4 = 1/16 and plywood down to 1/64 thickness is available in most hobby stores that cater to the model airplane crowd. If you give the entire boat a
            Message 5 of 13 , May 1, 2005
              1/4" x 1/4" = 1/16" and plywood down to 1/64" thickness is available in most hobby stores that cater to the model airplane crowd.

              If you give the entire boat a couple of coats of varnish (to seal it for floating purposes) and then a coat of paint, you'll approximate the weight of fiberglass, resin. and boat paint.

              Ron Fossum
              ----- Original Message -----
              From: Timtone
              To: Michalak@yahoogroups.com
              Sent: Sunday, May 01, 2005 8:05 AM
              Subject: Re: [Michalak] Re: Model in relation to ballast


              Right. OK. I get you. Makes sense.
              It might be a little tricky scaling a 1/4" ply hull thickness down to 1/4 size. ~:0)
              But there may be some kind of factor that would compensate for the 'natural' ballast of the boat...humans, gear batteries etc.
              I took donshultz's advice and went to the source for advice. I will share the result.

              Cheers, TT

              BTW.....Jim's newsletter essay on drawing and designing a hull is outstanding. I just came a cross it a few days ago. Finally, finding this info at a level my wee brain can comprehend. Eureka.



              [Non-text portions of this message have been removed]
            • David Davis
              ... design, does the ballast of that model relate in scale to the full scale version? ... and found 100 pounds worked well as ballast. Would this mean that 400
              Message 6 of 13 , May 1, 2005
                --- In Michalak@yahoogroups.com, "Timtone" <tim@t...> wrote:
                > Can anyone tell me if when you build a scale model of a proposed
                design, does the ballast of that model relate in scale to the full
                scale version?
                >
                > In other words, if you did a 1/4 scale model of a 20 foot boat,
                and
                found 100 pounds worked well as ballast. Would this mean that 400
                lbs.
                is going to work for the 20 footer?
                >
                > Thanks, Tim.

                Hi Tim,

                One might need to use the models design water line and compute the
                designed displacement of the model. Then uses the same percentage
                ballast on the model as was called for in the full size plans. If
                25%
                of the model's fully loaded displacement weight is ballast and will
                allow the model to recover from a 90 degree knockdown then the same
                may be true of the full size design. Likely the test results will
                depend on how well the design was modeled. Lead shot glued into the
                same spot as the planed ballast in the full size boat might work.

                Figure the models displacement at designned water line, add the
                percentage of designed model ballast, weigh the model, the
                difference
                between the model weight with ballast installed and the computed
                waterline displacement weight is usable model load carrying
                ability.
                to get a true "recovery from a knockdown" test you might want to add
                model crew weight where ever you think they might be seated.

                I am interested in water ballast, should be able to model that as
                well
                without great difficulty.

                Models in the 2 inches = one foot size might be able to be built
                using
                1/4 inch plywood without changing the waterline very much,
                especially
                with boats 15 foot and longer. No reason a model needs to be 1 inch
                =
                one foot -- the larger models might be easier to build with regular
                shop tools than the very small models. 1/4 scale or 3 inches = 1
                foot
                might be a little large to get into a car for the ride to the lake
                (depending on boat size - still thinking Cormorant size!) or pond
                and
                of course would cost a little more to build.

                David Davis
                >
              • Howard Stephenson
                If you try to take all the factors into account, this subject soon becomes very complicated. FOr example, it s not easy to scale down the thickness and weight
                Message 7 of 13 , May 1, 2005
                  If you try to take all the factors into account, this subject soon
                  becomes very complicated. FOr example, it's not easy to scale down
                  the thickness and weight per unit area of the paint or varnish needed
                  to protect the surface of the hull. And to make it worse, although
                  the displacement and weight of a 1/4 scale model is 1/64 of the
                  original, its surface area is 1/4 x 1/4 = just 1/16 of the original.
                  That's why racing model yachts often have unpainted carbon-fibre
                  hulls.

                  There are also considerations of stability and wind strength: you
                  can't scale down wind speed in proportion, yet the force exerted by
                  the wind is proportioanl to the square of its speed.

                  So it all depends on why you are building a model: is it to put on
                  the mantelpiece, to fool arond with in the swimming pool, or to sail
                  in real water with a real wind? There will have to be compromises
                  somewhere.

                  Howard

                  --- In Michalak@yahoogroups.com, "Ronald Fossum" <artemis@p...> wrote:
                  > 1/4" x 1/4" = 1/16" and plywood down to 1/64" thickness is
                  available in most hobby stores that cater to the model airplane crowd.
                  >
                  > If you give the entire boat a couple of coats of varnish (to seal
                  it for floating purposes) and then a coat of paint, you'll
                  approximate the weight of fiberglass, resin. and boat paint.
                  >
                  > Ron Fossum
                • John B. Trussell
                  Given the uncertainties of material weight, as well as gear and crew, I would take a pragmatic approach. Build the model, mark the waterline, put the model
                  Message 8 of 13 , May 1, 2005
                    Given the uncertainties of material weight, as well as gear and crew, I would take a pragmatic approach. Build the model, mark the waterline, put the model in the water, and add ballast until the model floats on her lines!

                    John T
                    ----- Original Message -----
                    From: Ronald Fossum
                    To: Michalak@yahoogroups.com
                    Sent: Sunday, May 01, 2005 3:36 PM
                    Subject: Re: [Michalak] Re: Model in relation to ballast


                    1/4" x 1/4" = 1/16" and plywood down to 1/64" thickness is available in most hobby stores that cater to the model airplane crowd.

                    If you give the entire boat a couple of coats of varnish (to seal it for floating purposes) and then a coat of paint, you'll approximate the weight of fiberglass, resin. and boat paint.

                    Ron Fossum
                    ----- Original Message -----
                    From: Timtone
                    To: Michalak@yahoogroups.com
                    Sent: Sunday, May 01, 2005 8:05 AM
                    Subject: Re: [Michalak] Re: Model in relation to ballast


                    Right. OK. I get you. Makes sense.
                    It might be a little tricky scaling a 1/4" ply hull thickness down to 1/4 size. ~:0)
                    But there may be some kind of factor that would compensate for the 'natural' ballast of the boat...humans, gear batteries etc.
                    I took donshultz's advice and went to the source for advice. I will share the result.

                    Cheers, TT

                    BTW.....Jim's newsletter essay on drawing and designing a hull is outstanding. I just came a cross it a few days ago. Finally, finding this info at a level my wee brain can comprehend. Eureka.



                    [Non-text portions of this message have been removed]



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                  • Timtone
                    Ronald, David and Howard. Too cool. Thanks very much for the input. My head hurts.... and there is a little smoke....but I will recover. I don t think in my
                    Message 9 of 13 , May 1, 2005
                      Ronald, David and Howard. Too cool. Thanks very much for the input.
                      My head hurts.... and there is a little smoke....but I will recover.

                      I don't think in my case, this is going to be too critcal.
                      I am just at the very beginnings of thinking about coming up with the design I want for myself. The waterline/model/ballast issue was just one of my first 'stumped' details. Many to come I am sure.
                      Just to see how it turns out, just a wee distraction. I have yet to find a design that quite fits my criterium.
                      If it turns out as planned at the model stage, then it might become a reality....but not soon.
                      I have put too much work into the boat I am currently sailing to move right into another any time soon.

                      I have been stimulated by the recent discovery of Jims Design essay. So I, went ahead and started to compile all of my details in one place. Soon to start coming up with some critical dimensions so I can eventually begin layout. Should be fun.

                      Cheer and thanks, Tim.

                      [Non-text portions of this message have been removed]
                    • Timtone
                      ... Thanks John T. That was the direction I was thinking. In my case, I figure a person could get pretty dang close just referring to historical data. Similar
                      Message 10 of 13 , May 1, 2005
                        >>Given the uncertainties of material weight, as well as gear and crew, I would take a pragmatic approach. Build the model, mark the waterline, put the model in the water, and add ballast until the model floats on her lines!

                        Thanks John T. That was the direction I was thinking. In my case, I figure a person could get pretty dang close just referring to historical data. Similar boat/ what ballast. Any discrepancies could be sorted with internal additions....or a Sawzall.

                        On this topic, I posted the same question to Jim. (as I mentioned before)
                        His reply was interesting and I thought you all might like to read it as well.

                        "I'm not sure you can learn anything from a boat model besides what it
                        looks like. Some folks disagree and Kilburn Adams told me he worked the
                        bugs out of his Skiff America design with a large powered RC model. As
                        for ballast calcs, they are related to stability. A lot easier to do now
                        that we have programs like Hullform. It the past it usually was not
                        calculated, only based on experience. I wrote an essay about the topic
                        based mostly on how to figure how much sail your boat can carry."

                        Does anyone know the title of that essay?

                        Cheers, Tim.

                        [Non-text portions of this message have been removed]
                      • Timtone
                        Excellent resource Chuck, thanks so much. [Non-text portions of this message have been removed]
                        Message 11 of 13 , May 1, 2005
                          Excellent resource Chuck, thanks so much.


                          [Non-text portions of this message have been removed]
                        • Chuck Leinweber
                          Tim: Jim wrote a lot of essays about sails. Check the index: HYPERLINK http://marina.fortunecity.com/breakwater/274/michalak/alphabetical.htm http ... Chuck
                          Message 12 of 13 , May 1, 2005
                            Tim:



                            Jim wrote a lot of essays about sails. Check the index:



                            HYPERLINK
                            "http://marina.fortunecity.com/breakwater/274/michalak/alphabetical.htm"http
                            ://marina.fortunecity.com/breakwater/274/michalak/alphabetical.htm



                            Chuck



                            _____

                            From: Michalak@yahoogroups.com [mailto:Michalak@yahoogroups.com] On Behalf
                            Of Timtone
                            Sent: Sunday, May 01, 2005 5:47 PM
                            To: Michalak@yahoogroups.com
                            Subject: [Michalak] Model in relation to ballast



                            >>Given the uncertainties of material weight, as well as gear and crew, I
                            would take a pragmatic approach. Build the model, mark the waterline, put
                            the model in the water, and add ballast until the model floats on her lines!

                            Thanks John T. That was the direction I was thinking. In my case, I figure
                            a person could get pretty dang close just referring to historical data.
                            Similar boat/ what ballast. Any discrepancies could be sorted with internal
                            additions....or a Sawzall.

                            On this topic, I posted the same question to Jim. (as I mentioned before)
                            His reply was interesting and I thought you all might like to read it as
                            well.

                            "I'm not sure you can learn anything from a boat model besides what it
                            looks like. Some folks disagree and Kilburn Adams told me he worked the
                            bugs out of his Skiff America design with a large powered RC model. As
                            for ballast calcs, they are related to stability. A lot easier to do now
                            that we have programs like Hullform. It the past it usually was not
                            calculated, only based on experience. I wrote an essay about the topic
                            based mostly on how to figure how much sail your boat can carry."

                            Does anyone know the title of that essay?

                            Cheers, Tim.

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