Developable hull

Discussion in 'Software' started by Newhill, Sep 26, 2013.

  1. Newhill
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    Newhill Junior Member

    Please, take a look at this hull, made in Freeship Plus 3.40.
    Should i be worried about the red colouring at the chine?
    By the way, has anyone made "cnc cutfiles" and successfully built a hull from freeship/delftship files?
     

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  2. lewisboats
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    lewisboats Obsessed Member

    That is the joint between panels. Naturally it can't be developed but the program tries to develop everything. Not to worry with that coloring.
     
  3. TANSL
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    TANSL Senior Member

    I have made many "cnc cutfiles" to build the structure of many boats and we can exchange all the information you want. It is a theme that I really like and would be happy to discuss with you.
    By the way, do not confuse "developable" surfaces and "ruled" surfaces. "Ruled" surfaces, which is what seems to have your boat, not always are developable.
     
  4. Newhill
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    Newhill Junior Member

    Thank you for responding. The screenshot is Freeships "developable check mode", so i guess it should be developable?
     
  5. TANSL
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    TANSL Senior Member

    Viewing the screenshot nobody can guarantee that they are, or are not, developable surfaces. But do not worry because there are procedures for developing non-developable surfaces, with sufficient accuracy. Freeship probably use one of these procedures.
     
  6. PAR
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    PAR Yacht Designer/Builder

    That's a nearly developed surface in a technical sense, but practically, it is, though there's a void in the edge tensions aft for some reason. The bow will fight you a bit, but other wise, you can "convince" panels to flow around these shapes.

    Of course, what the software doesn't tell you is if the hull shapes you've selected are very well suited to the requirements of the design brief. It'll just represent what you told it, regardless of how well or ill suited the hull form might be for the SOR.
     
  7. Jarek
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    Jarek Junior Member

    I'd say the best thing would be to read the manual. It has to state what any particular tool does.
    I do not know Freeship, I use Multisurf, in which if I want to have the surface fully developable, I use a special surface, called devsurf. It will always be 100% developable, unless the two curves used to create it are not in a proper relationship to each other. In extreme cases the surface creation will fail. I have a feeling the entity behaviour should be explained in the Help section of the particular software.
     
  8. Jarek
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    Jarek Junior Member

    Here is a possible sure solution. See if you are able to show the surface's Gaussian curvature. This should be all one colour if the surface is fully developable.
     
  9. Newhill
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    Newhill Junior Member

    Here is a picture of the gaussian mode. Same tinted edges as in developable mode.
    I have checked the help, and it says some "error" is normal.
    As Lewisboats mentioned.
    Jarek. Very nice boats on your homepage :)
     

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  10. Jarek
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    Jarek Junior Member

    Thank you.
    If they mean that the error is caused by the software not being perfect ( in general an error cannot be "normal" by definition),you are OK. It is free software.
    But if the error means (what it should mean), that the areas close to the edges of your plates are slightly non-developable (the colour coding should tell you by how much), you might want to fiddle with your chine curves until it is all light green.
    That said, I do not know how you generate your dev surfaces in Freeship. In mine a developable surface is generated between two longitudinal curves, top and bottom; because of that, it is not possible to have a non-developable area being generated in my software, along the whole edge of the surface. Do you have more control over the surface than two curves?
    If your surface is lofted through a number of transverse curves, a problem area along the edge could result. But lofting through curves is not an easy way to achieve a developable surface. Building a surface between two curves is much easier, provided it is both ruled and developable.
     
  11. TANSL
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    TANSL Senior Member

    Let me participate in this interesting discussion to ask the following question: can a developable surface be not-ruled?
     
  12. Jarek
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    Jarek Junior Member

    this one is simple: no.
     
  13. TANSL
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    TANSL Senior Member

    That's what I thought. So I missed the phrase:
    I've probably misunderstood. Thanks
     
  14. Jarek
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    Jarek Junior Member

    What I meant was that, just as a ruled surface can be developable, it is also possible to create a lofted surface that would be identical to a corresponding ruled and developable surface; but this would be very laborious.
    This comment, because, as far as I know in some NURBS programs (maybe most) you first create a surface, as an essentially generic rectangular "patch", then push and prod it so it looks like a hull side, and then ask the software to develop it. The software then offers options for doing that.
    In the software I use the only way to achieve a perfectly developable surface is to create it using ONLY two curves. This method always results in a ruled surface, and in a special case, the software can be asked to make it ruled and developable.
     

  15. TANSL
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    TANSL Senior Member

    I agree in what you say, what happens is that to say that it has been created a developable-ruled surface seems redundant. The otherwise, ruled-developable surface, is correct because a ruled surface can be non-developable.
    In most cases the program will present a surface, "patch", you have to adjust to your ship and at the end your boat looks pretty, though not equal, to what you wanted to do. So I prefer to create a body lines drawing, pass those lines to 3D and create surfaces by lofting between water lines or between frames. Although they are non-developable surfaces, do not worry, because there are procedures for developing non-developable surfaces with sufficient accuracy.
     
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