how to design in 3D

Discussion in 'Software' started by 1gerry, Jul 27, 2013.

  1. 1gerry
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    1gerry Junior Member

    So after some tweaking I think I am getting the gist of it.
    This is what it's looking like so far.

    Still has a bit of curve in the bow, but it's better.

    I wanted to make an all flat bottom, but since I'll be making this boat with plywood I am not sure I'll be able to do it nicely flat and tangent all the way to the bow.

    How this looking so far?
    Thanks
     

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  2. DCockey
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    DCockey Senior Member

    Plywood won't bend enough for the forefoot as drawn. Consider rounding the base of the stem and lifting the chine forward.

    How did you create the surfaces?
     
  3. 1gerry
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    1gerry Junior Member

    Hi,

    I created a surface with network surfaces, and then just moved the control points.

    I'll keep on working on the surfaces. I am concerned about the plywood not bending enough. I'll see what I can do.
    Would a shape like this be easier to make with plywood? Seems to me that it's be even harder.
     

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  4. DCockey
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    DCockey Senior Member

    Two limitations on bending plywood.

    First, plywood likes to bend in only one direction, no compound curvature, so the surfaces need to be what's called developable if the boat is to be built from large pieces of plywood. Lots of shapes are developable but shapes like spheres are not. Find a piece of thin cardboard or thick paper and experiment bending it to see what shapes are possible. Rhino has two good tools for designing developable shapes; Loft and DevSrf. Loft is a built-in command; set the style to "Developable". DevSrf needs to be downloaded and installed from the RhinoLab page on the Rhino website. http://wiki.mcneel.com/labs/devsrf I prefer DevSrf but Loft is simpler to start with.

    Second, plywood is limited in how sharp a radius it can be bent. Thinner plywood can be bent to a tighter radius.
     
  5. HakimKlunker
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    HakimKlunker Andreas der Juengere

    A boat of your size will be sensitive to weight trim. How about looking into a variety of trim situations and find out how the curve alters?
    A hollow waterline may not be that significant, when it allows a nice buttock line. I think, that boats are 4-dimensional in this respect.

    You will have a certain concept or major idea for your design.
    What I normally do, is to specify lines that I want on the boat under all circumstances; this may be a special frame section, or the DWL, or a sheer line.
    To start there, I often begin with 'curve from 2 views' and see what I can do all around it. If possible I will not alter my 'favourate features' until I find out that they do not correspond with the rest of the shape.

    I am not best friends with automatic functions. The program must not rule over the user (I avoid here to say 'designer).
     
  6. rwatson
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    rwatson Senior Member

    Well, heck - every boat is sensitive to trim. The bigger the boat the more weight you have to distribute.

    How a 'designer' can start talking about hull shapes before even doing the basic hydrostatics puzzles me no end.
     
  7. TANSL
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    TANSL Senior Member

    Perhaps I did not understand, but my question is this:
    How can a designer start talking about hydrostatic values ​​without a preliminary idea of hull shapes?.
    My opinión is that you need to have, by comparison with similar vessels, an idea of the main dimensions and hull coefficients for some displacement, but nothing more. From there, you have to raise preliminary shapes and then compute the hydrostatic values ​​to go properly fitting the puzzle pieces.
    Here everyone could comment on what would be the first steps to design a boat, once a specification is available or sufficient definition of what the boat should do.
    However, it seems to me that the creator of this thread is not interested at all in this discussion.
     
  8. rwatson
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    rwatson Senior Member

    " an idea of the main dimensions and hull coefficients for some displacement"

    That's hydrostatics, is it not ? By way of explanation, the first thing that I would consider is the weight table.


    For example, on a dinghy, you may have from 1 to 3 bodies, of certain weight ranges.

    Take a one man dinghy, your displacement will only need to be sufficient to float that body, at various places along the hull. ( eg Laser or Sabre)

    A three man dinghy will have to have considerably different hydrostatics. ( say Taser or Pacer ) and need more displacement.

    This thread starts as a 'shape', with no reference to the number of crew, for starters.
     
  9. DCockey
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    DCockey Senior Member

  10. TANSL
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    TANSL Senior Member

    I do not think that knowing the initial parameters of a hull has much to do with hydrostatic values​​. But it's my opinion, maybe it's a matter of semantics.
    Admittedly, these are topics for other thread that 1gerry has open.
     
  11. DCockey
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    DCockey Senior Member

    This thread is in the Software section, and the original question was specific to methods used to "draw" a new hull shape, not the overall design process.
     
  12. TANSL
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    TANSL Senior Member

    The initial question was: "how to design in 3D."
    Perhaps the first part of the answer is that for 3D design, first you need to make 2D work, doing calculations by hand, using a hand calculator or using the computer as "computer", not as a drawing tool.
     
  13. HakimKlunker
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    HakimKlunker Andreas der Juengere

    I have the impression that at this size of boat the overall expectable weight is relatively clear.
    What was unclear perhaps, was my previous statement - weight trim:
    I had crew weight on a dinghy in mind, because this is what we talk about - in this thread.
    Further, if one has two friends to sail with, and they differ in weight by 15 kg at on overall sailing weight (crew, boat, equipment) of say 250 kg, then a too 'accurate' weight design approach would be spoilt if this man/woman does not exactly position his/herself where the design placed her. That only worked on Roman galleys;)
     
  14. rwatson
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    rwatson Senior Member

    With a dinghy, it will be almost essential to move the weight around to trim - exactly, and the slightest inaccuracy will have substantial performance issues..

    It is part of the art of sailing dinghys - sometimes there will be two bodies close to the stern, with a strong stern wind. other times there will be two bodies hanging way out one side - because the wind is a such a major component of the sailing.

    The thing is, that you have to plan on having sufficient bouyancy to cope with all types of bodies locations, not just in their optimal positions.

    I can tell you now, that the designer of the 12ft Mirror dinghy made absolutely no allowance for 115 kilo person standing on the bow, slightly off centre, I admit.
     

  15. DavidJ
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    DavidJ Senior Member

    Initial parameters and weight estimate are very important, but they are NOT hydrostatics.

    I make hulls very much like the other David described.

    Hull fairing is an art although it is an art that can be learned. Practice practice practice. Nudging control points. Build and rebuilt surfaces. Inspect the curvature graph of your curves for unwanted direction changes. Use the environment map and/or zebra to spot surface irregularities. Pay close attention to your isocurves when you create a surface. And of course use the smallest number of control points in your curves and surfaces that get the shape you want. Then practice practice practice.
     
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