getting the shape based on existing flat panels?

Discussion in 'Boat Design' started by rnlock, Aug 2, 2016.

  1. rnlock
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    rnlock Senior Member

    I found a design for a simple one sheet boat, but I only have the panels, not the developed shape. Usually people are going the other way, but in this case I want to know what happens if you cut out these shapes and put them together. Including displacement and stuff like that. I suppose I could make a balsa model and measure, but considering that I have Solidworks and some other software, there must be a more accurate way. This would also be good if I was designing something to fit on plywood sheets. Or if I wanted to figure out the displacement and other properties of one of Bolger's Instant Boats. Not looking to spend dough on this. Not averse to a manual or spreadsheet method if it's moderately easy and quick.



    P.S. For those of you not familiar with one sheet boats, they can be an interesting problem. Here are a couple of sites with designs. Some of them displace more than you'd expect. aka Hannu's boat yard
    There's also a Yahoo group called One Sheet Wonders
    I think, for me, I'd need to use a bigger sheet of plywood!
  2. TANSL
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    TANSL Senior Member

    Would it be possible to have a look at the information you have to see if it is viable to do what you want with sufficient accuracy?
  3. bajansailor
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    bajansailor Marine Surveyor

  4. rnlock
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    rnlock Senior Member

    bajansailor's post contains a design which is fairly close to one design I want to check out like this. The one I was thinking about, at least at first, was the Shamrock one sheet boat by Philip McCracken:
    Note that it is very similar to the one bajansailor linked to, except that it uses the plywood much more efficiently and so has a larger displacement.

    I realize, since there is only one mold between the bow and the transom, that the geometry probably varies from boat to boat, but I think it should be possible to get close.
  5. Petros
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    Petros Senior Member

    you can spend many hours messing with computer programs and not be satisfied. I have found it is more fun, faster and give you a better feel for it if you just lay out the pattern on heavy paper, or cardboard, at a convenient scale (perhaps 2" to the foot), cut it out and tape it together. balsa is too expensive and too hard to join accurately at small scale. stiff paper or cardboard is much better, and cheaper.

    It will actually teach you about how the panels will have to be bent or tortured to fit together. and give you a nice physical model to look at, play with, hold in your hands, etc.

    If you have kids, scale to fit a barbie or a GI joe, use waxed cardboard and duct tape, and let them have fun with it after you are done playing with it.

    As one of my engineering professors used to say: One simple test build like this is worth a thousand expert opinions, and I have found worth 1000 hours of trying to model it on a computer.

    Do not over think it: Get away from your desk and go out and built it already. You are only taking about one sheet of plywood.
  6. rnlock
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    rnlock Senior Member

    Actually, I did make a card stock model. Very squishy. I now have a vague idea what it would look like, though I have more faith in the photos.

    I find balsa far more precise, actually. And I'm comfortable working with it.

    In any case, in part I'm looking for qualitative answers to qualitative problems. I suppose if I made a REALLY careful balsa model, I could see how much displacement it has at a reasonable waterline.

    I am used to designing stuff on a computer and getting good results. I've also designed and built a pram to hold a friend, his wife, and some groceries, that he could fit between the rails on the ramp at Marblehead. The displacement number came out about right, keeping the transom and the bow out of the water. I finished up two other people's boat projects as well.

    In the past, people have told me to take a less technical approach, but in that case, I lose a lot of the fun of it.
  7. SukiSolo
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    SukiSolo Senior Member

    Exactly right, what's a few minutes or even hours fiddling with a test mockup to prove it is right or wrong, fixable etc compared to the hours in the end product?
    Manys the time a bit of cardboard wood or whatever, a few pins etc etc has saved hours and proved principles early on in a project. Even with all the excellent CAD tools available I still see some basic errors in stuff. Maybe 'old school' but I find prototypes etc invaluable. With the best will in the world there is nearly always some minor detail not quite so, nice to catch it as early as possible.

    Good luck with your project, btw I think Rhino can fit the developed panels into the shape they were derived from.
  8. rnlock
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    rnlock Senior Member

    Sadly, my CAD budget has been exhausted by purchasing Solidworks! I'm sure there's a way, possibly even without spending more money, but I haven't been clever enough to figure it out yet. I'm pretty sure a more expensive version of Solidworks can do it. There's some function for surfaces called "flatten".
  9. DCockey
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    DCockey Senior Member

    Starting with a collection of flat panels and "rolling" them into a hull shape is mathematically a much, much more difficult problem then unrolling the panels flat a developable hull shape.

    Each of the flat panels can be rolled into an infinite variety of shapes. The challenge is to find the shape for each panel which has the edges meeting.
    1 person likes this.
  10. SukiSolo
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    SukiSolo Senior Member

    Note David's correct comments, rnlock. Solidwoks will give you developed surfaces but for reversing it you need diferent tools. That's where curve control especially length constraint and measurement is key, along with editing tools allow you to find the original shape. It's a bit tedious but I have refited developed panels manually inside a program to within 0.5mm before now. You also have to have enough of a feel for where the shape should go, otherwise it's like blind mans buff.

    Only worth doing on simple forms otherwise you will have great difficulty resolving where the edges are in space. If you have the advantage of photographs or renderings you may be able to use these as backgrounds to help fit the curves.

    Not sure about current Solidworks but the flatten function may be a Sheet metal biased tool. I have taken SW IGES surfaces for real aircraft wings and turned them into correct developed surfaces in Rhino before now. These were in aluminium and the analysis tools also showed exactly where the material required minor stretch to fit.
  11. rnlock
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    rnlock Senior Member

    Yow. That sounds like an awful lot of work! I looked at the sheet metal stuff for Solidworks, but I don't see anything that would do this. Sheet metal seems to require simple curves. Maybe just cylindrical radii type. I'm not sure.
  12. PAR
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    PAR Yacht Designer/Builder

    A simple solution might be just to 3D scan (photogrammetry) an assembled model, of a reasonable scale. You'll get a point cloud that can be manipulated in Rhino or SolidWorks, or whatever. My software has a "scan to mesh" option which makes this a pretty simple deal. I don't use SolidWorks, but would imagine it too can handle a point cloud or vectored model. I do know AutoDesk has some software that can do this easily.
  13. Doug Halsey
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    Doug Halsey Senior Member

    You need more than just the flat-panel shapes (and the requirement that the edges match) to determine what the shape of the boat will be. So there is no unique solution.

    In stitch & glue construction, the builder can change the shape a lot, depending on the angles at which he forces the panels to meet & the overall beam that he bends it into.

    A few minutes playing with paper cutouts should convince you of that.

  14. rwatson
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    rwatson Senior Member

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