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Boat Offsets and Stitch n Tape

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  • imduds
    Hello, I have a question regarding boat lofting for stitch and tape. Its slightly off topic for bolger but very relevant in boat building. Is there a
    Message 1 of 15 , Feb 28, 2002
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      Hello, I have a question regarding boat lofting for stitch and tape.
      Its slightly off topic for bolger but very relevant in boat building.

      Is there a mathematical method to develop the shapes for stitch n
      glue construction of a chined boat from offsets.

      My method until this point is to model the boat from offsets and then
      transfer the shapes from the model. Unfortunately this method is
      prone to some errors as well as requiring a model to be built. I know
      that there is some CAD software that can do this automatically,
      however I would prefer a method by hand or using a spreadsheet or
      tables.

      Thanks in advance for your help.

      I am planning a replica 'Egret' Sharpie reduced to 5.4m 18'.

      PS if anyone is interested I have created a great little spreadsheet
      for converting offsets from ',",18ths to mm and reducing or
      increasing scale and producing scaled offsets for models.

      Regards Dale
    • tom28571
      There is no magic method to solve your problem that I know of. Building a model and lifting the panel shapes and then enlarging them works but, as you say,
      Message 2 of 15 , Feb 28, 2002
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        There is no magic method to solve your problem that I know of.
        Building a model and lifting the panel shapes and then enlarging them
        works but, as you say, there is the probability of error.

        If you have the offsets and know that the shape is "developable" in
        plywood, then you can loft full size from the offsets.

        If you just want to make the boat shorter and retain the beam, you
        can reduce the station spacing and proceed as above to loft it.

        Willi-nilly changing the size of a boat opens up other problems.

        Computer programs exist to generate panel shapes from offsets but
        they are not generally foolproof and require some practical knowlege
        of the difference between theoretical surfaces and real materials, or
        so I am informed by those who do this.

        After I had completed the design of my latest boat, I had one of
        these gurus to feed it into his software (Autoyacht) which faired the
        lines (lofted) and generated the panel layouts. That option is open
        if you can find a designer to do this for you.

        --- In bolger@y..., "imduds" <dalerogers@m...> wrote:
        > Hello, I have a question regarding boat lofting for stitch and tape.
        > Its slightly off topic for bolger but very relevant in boat
        building.
        >
        > Is there a mathematical method to develop the shapes for stitch n
        > glue construction of a chined boat from offsets.
        >
        > My method until this point is to model the boat from offsets and
        then
        > transfer the shapes from the model. Unfortunately this method is
        > prone to some errors as well as requiring a model to be built. I
        know
        > that there is some CAD software that can do this automatically,
        > however I would prefer a method by hand or using a spreadsheet or
        > tables.
        >
        > Thanks in advance for your help.
        >
        > I am planning a replica 'Egret' Sharpie reduced to 5.4m 18'.
        >
        > PS if anyone is interested I have created a great little
        spreadsheet
        > for converting offsets from ',",18ths to mm and reducing or
        > increasing scale and producing scaled offsets for models.
        >
        > Regards Dale
      • rlspell2000
        Why don t you send Jim Michalak an email? He developes his panels by hand, so he should have the method down. ... building. ... then ... know ... spreadsheet
        Message 3 of 15 , Feb 28, 2002
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          Why don't you send Jim Michalak an email? He developes his panels by
          hand, so he should have the method down.

          --- In bolger@y..., "imduds" <dalerogers@m...> wrote:
          > Hello, I have a question regarding boat lofting for stitch and tape.
          > Its slightly off topic for bolger but very relevant in boat
          building.
          >
          > Is there a mathematical method to develop the shapes for stitch n
          > glue construction of a chined boat from offsets.
          >
          > My method until this point is to model the boat from offsets and
          then
          > transfer the shapes from the model. Unfortunately this method is
          > prone to some errors as well as requiring a model to be built. I
          know
          > that there is some CAD software that can do this automatically,
          > however I would prefer a method by hand or using a spreadsheet or
          > tables.
          >
          > Thanks in advance for your help.
          >
          > I am planning a replica 'Egret' Sharpie reduced to 5.4m 18'.
          >
          > PS if anyone is interested I have created a great little
          spreadsheet
          > for converting offsets from ',",18ths to mm and reducing or
          > increasing scale and producing scaled offsets for models.
          >
          > Regards Dale
        • steelcb
          Dale, Don t know if this is what you have in mind, but I have been using the chine designer software I downloaded through the files section to develop some
          Message 4 of 15 , Feb 28, 2002
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            Dale,

            Don't know if this is what you have in mind, but I have been using
            the chine designer software I downloaded through the "files" section
            to develop some interesting hull shapes which I modeled in cardboard.


            I recently developed an Indian-style canoe that caught my fancy
            enough that I'm transferring it to full size and building it at about
            the 16 ft length. I am getting the full-size chine shapes by
            printing out the chines on a laser printer at the size the software
            generates(I don't have a plotter which prints full size I've read).

            After printing them out, I scanned in those images and inserted these
            scanned images into Micrsoft Powerpoint slides. I adjusted these
            inserted images to take up a whole page and superimposed a gridwork
            of squares over this image representing 1 1/2" per square(I assumed
            an 8' length for the image and started halving the distances to get
            this set of grid lines). Using this gridwork, I determined the
            coordinates for set points every foot for a 4' X 8' sheet. I have now
            transferred these points to a 4' X 8' sheet of thin paneling to cut a
            pattern. I did this by drawing one foot lines on the paneling and
            transferring the calculated measurements onto these lines.

            I also had to transfer the end points of the chines(a little more
            difficult). After these points were all transferred to the paneling
            sheet, I used a 1" X 1/4" X 9' batten and some small nails to lay out
            the curved chine shapes. The software prints out shapes that have
            straight lines roughly approximating a curve, but the batten should
            make these chines smoother and hopefully still fit.

            I am at the halfway point now, getting ready to prepare the other
            half of the pattern(2nd 4 x 8 sheet). You only have to lay out half
            of the chines, since the other side of the hull is obtained by
            turning them over.

            I haven't finished this process yet, but it looks promising. I will
            attempt to iron out any mis-matches in the chines while in the
            pattern stage, so when I cut out the luan pieces they will fit
            adequately. Stitch-n-glue likes a sloppy joint anyway, because more
            of the epoxy gets into a rough joint.

            This method is not specifically mathematical, being more graphically
            derived, but I think it will do what I plan, and has the benefit of
            being free assuming access to a graphic program like
            Powerpoint(except
            for materials). Actually, if you have a few drafting skills, you
            could just take a printout of the chine shapes and draw this grid
            over it with pen & ink. I may have gone overboard with the
            Powerpoint, but I work long nights and it keeps me busy.

            Hope this helps.

            Tom Pannell
            Tulls Bay, NC


            > Hello, I have a question regarding boat lofting for stitch and tape.
            > Its slightly off topic for bolger but very relevant in boat
            building.
            >
            > Is there a mathematical method to develop the shapes for stitch n
            > glue construction of a chined boat from offsets.
            >
            > My method until this point is to model the boat from offsets and
            then
            > transfer the shapes from the model. Unfortunately this method is
            > prone to some errors as well as requiring a model to be built. I
            know
            > that there is some CAD software that can do this automatically,
            > however I would prefer a method by hand or using a spreadsheet or
            > tables.
            >
            > Thanks in advance for your help.
            >
            > I am planning a replica 'Egret' Sharpie reduced to 5.4m 18'.
            >
            > PS if anyone is interested I have created a great little
            spreadsheet
            > for converting offsets from ',",18ths to mm and reducing or
            > increasing scale and producing scaled offsets for models.
            >
            > Regards Dale
          • rlspell2000
            emmm. Gregg s hulls program, which is what i m assuming you are using, will print out a handplot file, with the offsets in it for hand measuring... ...
            Message 5 of 15 , Feb 28, 2002
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              emmm. Gregg's hulls program, which is what i'm assuming you are
              using, will print out a "handplot" file, with the offsets in it for
              hand measuring...

              --- In bolger@y..., "steelcb" <steelcb@y...> wrote:
              > Dale,
              >
              > Don't know if this is what you have in mind, but I have been using
              > the chine designer software I downloaded through the "files"
              section
              > to develop some interesting hull shapes which I modeled in
              cardboard.
              >
              >
              > I recently developed an Indian-style canoe that caught my fancy
              > enough that I'm transferring it to full size and building it at
              about
              > the 16 ft length. I am getting the full-size chine shapes by
              > printing out the chines on a laser printer at the size the software
              > generates(I don't have a plotter which prints full size I've
              read).
              >
              > After printing them out, I scanned in those images and inserted
              these
              > scanned images into Micrsoft Powerpoint slides. I adjusted these
              > inserted images to take up a whole page and superimposed a gridwork
              > of squares over this image representing 1 1/2" per square(I assumed
              > an 8' length for the image and started halving the distances to get
              > this set of grid lines). Using this gridwork, I determined the
              > coordinates for set points every foot for a 4' X 8' sheet. I have
              now
              > transferred these points to a 4' X 8' sheet of thin paneling to cut
              a
              > pattern. I did this by drawing one foot lines on the paneling and
              > transferring the calculated measurements onto these lines.
              >
              > I also had to transfer the end points of the chines(a little more
              > difficult). After these points were all transferred to the
              paneling
              > sheet, I used a 1" X 1/4" X 9' batten and some small nails to lay
              out
              > the curved chine shapes. The software prints out shapes that have
              > straight lines roughly approximating a curve, but the batten should
              > make these chines smoother and hopefully still fit.
              >
              > I am at the halfway point now, getting ready to prepare the other
              > half of the pattern(2nd 4 x 8 sheet). You only have to lay out
              half
              > of the chines, since the other side of the hull is obtained by
              > turning them over.
              >
              > I haven't finished this process yet, but it looks promising. I
              will
              > attempt to iron out any mis-matches in the chines while in the
              > pattern stage, so when I cut out the luan pieces they will fit
              > adequately. Stitch-n-glue likes a sloppy joint anyway, because
              more
              > of the epoxy gets into a rough joint.
              >
              > This method is not specifically mathematical, being more
              graphically
              > derived, but I think it will do what I plan, and has the benefit of
              > being free assuming access to a graphic program like
              > Powerpoint(except
              > for materials). Actually, if you have a few drafting skills, you
              > could just take a printout of the chine shapes and draw this grid
              > over it with pen & ink. I may have gone overboard with the
              > Powerpoint, but I work long nights and it keeps me busy.
              >
              > Hope this helps.
              >
              > Tom Pannell
              > Tulls Bay, NC
              >
              >
              > > Hello, I have a question regarding boat lofting for stitch and
              tape.
              > > Its slightly off topic for bolger but very relevant in boat
              > building.
              > >
              > > Is there a mathematical method to develop the shapes for stitch n
              > > glue construction of a chined boat from offsets.
              > >
              > > My method until this point is to model the boat from offsets and
              > then
              > > transfer the shapes from the model. Unfortunately this method is
              > > prone to some errors as well as requiring a model to be built. I
              > know
              > > that there is some CAD software that can do this automatically,
              > > however I would prefer a method by hand or using a spreadsheet or
              > > tables.
              > >
              > > Thanks in advance for your help.
              > >
              > > I am planning a replica 'Egret' Sharpie reduced to 5.4m 18'.
              > >
              > > PS if anyone is interested I have created a great little
              > spreadsheet
              > > for converting offsets from ',",18ths to mm and reducing or
              > > increasing scale and producing scaled offsets for models.
              > >
              > > Regards Dale
            • rnlocnil
              Michalak sells a book on designing plywood boats which discusses this. He also makes reference to a book by Rable which is where he got the technique. But
              Message 6 of 15 , Feb 28, 2002
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                Michalak sells a book on designing plywood boats which discusses this.
                He also makes reference to a book by Rable which is where he got the
                technique. But doesn't Hulls, or whatever it's called, do this?
                --- In bolger@y..., "rlspell2000" <richard@s...> wrote:
                > Why don't you send Jim Michalak an email? He developes his panels by
                > hand, so he should have the method down.
                >
                > --- In bolger@y..., "imduds" <dalerogers@m...> wrote:
                > > Hello, I have a question regarding boat lofting for stitch and
                tape.
                > > Its slightly off topic for bolger but very relevant in boat
                > building.
                > >
                > > Is there a mathematical method to develop the shapes for stitch n
                > > glue construction of a chined boat from offsets.
                > >
                > > My method until this point is to model the boat from offsets and
                > then
                > > transfer the shapes from the model. Unfortunately this method is
                > > prone to some errors as well as requiring a model to be built. I
                > know
                > > that there is some CAD software that can do this automatically,
                > > however I would prefer a method by hand or using a spreadsheet or
                > > tables.
                > >
                > > Thanks in advance for your help.
                > >
                > > I am planning a replica 'Egret' Sharpie reduced to 5.4m 18'.
                > >
                > > PS if anyone is interested I have created a great little
                > spreadsheet
                > > for converting offsets from ',",18ths to mm and reducing or
                > > increasing scale and producing scaled offsets for models.
                > >
                > > Regards Dale
              • pippobianco
                Dale, there are free programs like Robert Lainé s Carene which rigorously develop conical surfaces. There s also Unfold which does the same starting from
                Message 7 of 15 , Mar 1, 2002
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                  Dale, there are free programs like Robert Lainé's "Carene" which
                  rigorously develop conical surfaces. There's also "Unfold" which does
                  the same starting from a table of offsets, but it assumes that the
                  surface is developable. Gregg's "Hull Designer", while much better
                  than the others in terms of user interface, does not (yet?) perform a
                  rigorous developability check. You have to use common sense when
                  working on strongly flared sections of the boats (for example,
                  modeling the Chebacco hull is practically impossible at the bow).
                  Of course many commercial hull fairing programs do the plate
                  development.
                  The best description of the conical development method I've seen is
                  in John Teale's "How to design a boat". Also Stephen
                  Pollard's "boatbuilding with aluminum" has a good description.
                  For what I know, the most used algorithm is the Kilgore's one, first
                  described in some publication on fishing boats in the third world
                  (FAO or some similar organization).
                  Best, Pippo


                  > Is there a mathematical method to develop the shapes for stitch n
                  > glue construction of a chined boat from offsets.
                • brucehallman
                  ... I recall reading that Jim Michalak uses the method of joining triangles. I.E. A piece of curved plywood can always be reduced to a grid of ajoined
                  Message 8 of 15 , Mar 1, 2002
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                    --- In bolger@y..., "rlspell2000" <richard@s...> wrote:
                    > Why don't you send Jim Michalak an email?
                    > He developes his panels by
                    > hand, so he should have the method down.

                    I recall reading that Jim Michalak uses the method of joining
                    triangles. I.E. A piece of curved plywood can always be reduced to
                    a grid of ajoined triangles with the length of the legs determined.
                    If you flatten out the group of triangles, then you know the shape of
                    the plywood to cut.

                    In other words, draw a zig-zag line from edge to edge for the full
                    length of each plywood panel, each of the spaces between the lines
                    and plywood edge is a triangle. The length of the lines is the same
                    whether the plywood is bent or flat. You know the length of each
                    line, so you can layout your cuts.
                  • pvanderwaart
                    ... It s all based on the concept that the ply doesn t stretch, so the triangles all stay the same size and shape. Suppose you have a chine hull drawn with the
                    Message 9 of 15 , Mar 1, 2002
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                      > I recall reading that Jim Michalak uses the method of joining
                      > triangles.

                      It's all based on the concept that the ply doesn't stretch, so the
                      triangles all stay the same size and shape. Suppose you have a chine
                      hull drawn with the usual 11 stations (0-10). To lay out the
                      topsides, you could start with the triangle that has the base at the
                      chine and rail at station 5, and the peak at the rail on station 6.
                      The next triangle would have a base at the chine and rail at station
                      6 and the peak on the chine at station 5. Etc, both ways.

                      So far as I know, all the fancy software works basically the same
                      way, except they use a larger number of stations (and/or cleverly
                      chosen triangles) to cut down the error.

                      Exercise for the student: What happens when you try this process with
                      a "non-developable" hull shape? Hint: the trouble begins because the
                      straight-line length of a triangle side is not the same as the length
                      measured along the curve of the hull.

                      Peter
                    • ghartc
                      I wrote the Hulls program freeware which you can get from carlsondesign.com. You design in 3D and it develops the flat panels to cut. You can model an
                      Message 10 of 15 , Mar 1, 2002
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                        I wrote the "Hulls" program freeware which you can get from
                        carlsondesign.com. You design in 3D and it develops the flat panels
                        to cut. You can model an existing design, which you know is
                        "developable". On a scratch design, my program doesn't restrict you
                        to conical development (which means each panel lies on a cone or
                        cylinder), mainly because it doesn't know how. In Hulls, you can
                        freely bend and twist panels, so they *might* be tortured.

                        It's a little like bumblees flying - they can't fly, but since they
                        don't know that, they do anyway. Practically, what happens when you
                        really bend and twist is that your panel might want to "cup" some
                        from the straight line segments going around the bulkhead. The
                        program doesn't know any different. You might see some in short, fat
                        panels/boats with a lot of torture, though it's generally less
                        than "manufacturing" (sawing and epoxy-ing) tolerances.

                        Actually, its a lot more intuitive than it sounds - what looks
                        pleasing to the eye and streamlined to the water is not going to be
                        tortured much if at all. So, lots of hulls get built by people who
                        never heard of donical cevelopment. (Pls send your broadsides to me
                        directly.)

                        {That's the difference between engineers or "applied scientists"
                        (like me) who design to +/-10% and get it built, and scientists who
                        enjoy rigor. But, I will concede here that I will NOT be volunteering
                        for the Mars shot that makes it 90% or so of the way back to earth;-}

                        To output, you can 1.) send the hulls output to a sailmaker who has
                        one of my plotting machines and would put it on paper for you, 2.)
                        find a draftsman with a big roll paper plotter and give him the HPGL
                        or DXF output to plot, 3.) use the handplot.txt and tape meausure to
                        loft out the panels, or 4.) under the hulls nesting feature, nest the
                        panels and plot them directly, X by Y, onto the plywood as shown by
                        the program. The optical method sounds like a lot of extra work (?)

                        Gregg Carlson
                        www.carlsondesign.com

                        --- In bolger@y..., "steelcb" <steelcb@y...> wrote:
                        >Don't know if this is what you have in mind, but I have been using
                        >the chine designer software I downloaded through the "files" section
                        >to develop some interesting hull shapes which I modeled in cardboard.
                        >
                        >After printing them out, I scanned in those images and inserted
                        >scanned images into Micrsoft Powerpoint slides. I adjusted these
                        >inserted images to take up whole page and superimposed a gridwork...
                      • steelcb
                        Greg, I ve enjoyed your hulls software immensely. It provides such scope for the imagination. I don t worry about how it works, I just use it for hours on
                        Message 11 of 15 , Mar 1, 2002
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                          Greg,

                          I've enjoyed your hulls software immensely. It provides such scope
                          for the imagination. I don't worry about how it works, I just use it
                          for hours on end pulling and pushing and contemplating the new hull
                          shapes. It works well for designing decks and structures, wings, and
                          fuselages too. Thanks a million.

                          Tom Pannell
                          Tulls Bay, NC

                          --- In bolger@y..., "ghartc" <gcarlson@c...> wrote:
                          > I wrote the "Hulls" program freeware which you can get from
                          > carlsondesign.com. You design in 3D and it develops the flat panels
                          > to cut. You can model an existing design, which you know is
                          > "developable". On a scratch design, my program doesn't restrict you
                          >
                        • jhkohnen@boat-links.com
                          THE book on developing panel shapes is: Ship And Aircraft Fairing And Development for Draftsmen and Loftsmen and Sheet Metal Workers by Sam Rabl It s available
                          Message 12 of 15 , Mar 2, 2002
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                            THE book on developing panel shapes is:

                            Ship And Aircraft Fairing And Development for Draftsmen and Loftsmen and
                            Sheet Metal Workers by Sam Rabl

                            It's available for reasonable prices used (see http://www.abe.com), but
                            I've also heard that it's been reprinted recently (or maybe it never went
                            out of print?).

                            Yes, that's the same Sam Rabl who wrote Boatbuilding in Your Own Back Yard.


                            --
                            John <jkohnen@...>
                            http://www.boat-links.com/
                            Nobody ought to wear a Greek fisherman's hat unless they meet two conditions:
                            1. He is a Greek
                            2. He is a Fisherman <Roy Blount Jr.>
                          • David Romasco
                            Westie Farmer had some great tales about Sam s experience in designing a flash amphibian aircraft, worth looking up at the library ( My Old Boat Shop ). Good
                            Message 13 of 15 , Mar 2, 2002
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                              Westie Farmer had some great tales about Sam's experience in designing a
                              flash amphibian aircraft, worth looking up at the library ('My Old Boat
                              Shop'). Good book anyway, no matter what Thomas Firth Jones says..

                              David Romasco

                              -----Original Message-----
                              From: jhkohnen@... [mailto:jhkohnen@...]
                              Sent: Saturday, March 02, 2002 1:21 PM
                              To: bolger@yahoogroups.com
                              Subject: Re: [bolger] Re: Boat Offsets and Stitch n Tape

                              THE book on developing panel shapes is:

                              Ship And Aircraft Fairing And Development for Draftsmen and Loftsmen and
                              Sheet Metal Workers by Sam Rabl

                              It's available for reasonable prices used (see http://www.abe.com), but
                              I've also heard that it's been reprinted recently (or maybe it never
                              went
                              out of print?).

                              Yes, that's the same Sam Rabl who wrote Boatbuilding in Your Own Back
                              Yard.


                              --
                              John <jkohnen@...>
                              http://www.boat-links.com/
                              Nobody ought to wear a Greek fisherman's hat unless they meet two
                              conditions:
                              1. He is a Greek
                              2. He is a Fisherman <Roy Blount Jr.>






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                            • filmokentucky@aol.com
                              Please unsuscribe me
                              Message 14 of 15 , Mar 2, 2002
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                                Please unsuscribe me
                              • ravenouspi
                                ... If you are taking this group via email, simply click on the Unsubscribe link at the end of your message (it comes in every single email post you receive
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                                  --- In bolger@y..., filmokentucky@a... wrote:
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