Rhino: make a curved bow on a developable plank

Discussion in 'Software' started by Renaud Chile, Jul 2, 2019.

  1. Renaud Chile
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    Renaud Chile New Member

    Hello, I'm working on the plan of a simple hard chine plywood canoe with Rhino (3.0). Whenever I do this type of plan, I can never get a curved bow.
    [​IMG]
    I have already seen professional designers get curved bow with Rhino; I do not know how they do it :(

    I manage to get a curved bow by adding control points to the bow, but this makes the plank undevelopable ... And my goal is to unroll the planks to be able to draw the planks on the plywood plate.
    [​IMG]
    How to succeed (elegantly) to get the drawing of a curved bow on the flat plywood plate ...

    Thank you in advance !

    Renaud (I am French and sorry for my low level of English).
     

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  2. Mr Efficiency
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    Mr Efficiency Senior Member

    You want it to look, in profile, like a conventional canoe ? Well, that curved canoe bow comes from the conjunction of curved sides, whereas with ply they are more or less straight sides. Hence little curve to the bow profile. Why are you averse to what the developable shape gives you, as a bow profile ? It doesn't "look right" ??? I think you just have to put that prejudice aside, and proceed with what is practicably obtainable.
     
  3. jehardiman
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    jehardiman Senior Member

  4. bhnautika
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    bhnautika Senior Member

    Renaud Chile Here is a method you may like to try. The trick here is to put the curve in the side of the sheet not in the end. If you look at the quick model I set up, you see I have put the stem curve in the bottom/keel (blue line) with a small end line (red). So as not to add to many points in order to get a clean curve I used the “edit weight” command and ajusted the weighting of the first point (to 2) and dragged it to where I wanted. Then made a surface, un-rolled it stem curve.png
     
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  5. jehardiman
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    jehardiman Senior Member

    Yeah, that forces a quasi-conic development if I recall how Rhino works correctly (i.e. the very small last panel is actually tortured/undevelopable). The only issue is if there is an exact curve you are trying to fit...but good enough is mostly better than perfect for developed plates.
     
  6. Mr Efficiency
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    Mr Efficiency Senior Member

    I was assuming he wanted the part above the chine to form a curved bow profile, but if not, disregard what I said !
     
  7. jehardiman
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    jehardiman Senior Member

    Same difference, it could be conically developed...just Renaud's shortcut wouldn't work...you'd have to develop each section and then stich them together (shades of AeroHydro MultiSurf).

    Edit to add; This is not really new, a lot of the poly-conically developed planeing hulls and aircraft fuselages from the 1930's and '40's where done this way by hand.
     
  8. Mr Efficiency
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    Mr Efficiency Senior Member

    The drawing isn't clear to me, is there a flat bottom as well ? Anyway, it appears to me his concern is the "forefoot", which is what he has the arrow pointed toward.
     
  9. rwatson
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    rwatson Senior Member

    Often, it's easier to just experiment with the different bow and keel arrangements that "look" developable.

    I have found, that if you use the "Sweep 2 Rails Command when putting a Surface on a Hard Chine design, it tends to split the Surface into two Developable Surfaces when the turns are too tight.
    Sweep2.png

    In this example, the Surface for the Bottom part of the Hull actually split itself into two Surfaces, that Unroll fine with little deviation. The Red Line on this illustration shows where the "break" occurred.
    Develop.png

    I haven't experimented with an idea I had a while ago, that instead of using the whole Chine and Keel line when creating a Surface, if you carefully ruled transverse "station" lines, and made sure they followed the "Ruled" development (to get Conical Sections) - you could then use Sweep2Rails on sections of the hull, instead of the whole bottom of the hull.
    In other words, the Yellow Lines in this diagram could be created by the designer, and each section would be created individually. In practice, you would use a lot less "station" lines than Rhino created in this example.

    I found careful attention to the "Curve Graph" results is a big influence too.
    CurveGraph.png
    You will notice that the "jump" in the Curve Graph is where the Sweep2Rails Command "broke" the hull surface.

    This Curve Graph was obtained after the Fair command was used on the Keel Line.

    Then, by deleting a few Control Points on the Keel line, and using Fair, the Curve Graph was vastly improved, and Sweep2Rails produced a complete hull section.

    CurveGraph2.png
     
  10. Renaud Chile
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    Renaud Chile New Member

    I'm not opposed to that, it's just Rhino who does not want to develop my plank later !
     
  11. DCockey
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    DCockey Senior Member

    Extend the edge curves (sheer curve and chine curve) beyond the stem, create a developable surface between the edge curves, and then trim the surface using a plane on the center of the hull. The stem of a hull made of developable surfaces should be curved unless the stem coincides with a ruling line.

    The Loft command prior to Rhino 6 had a Developable option which created a developable surface between two edge curves. It does have the disadvantage of creating a triangular conical sections at the ends when the corresponding ends of the edge curves do not lie on a untwisted ruling line.

    The DevSrf command is available for Rhino 4 and later versions. It creates a developable surface between edges curves. The Rhino 6 version of DevSrf is available at DevSrf https://www.food4rhino.com/app/devsrf The Rhino 4 and Rhino 5 versions of DevSrf are available at Developable Surface Construction [McNeel Wiki] https://wiki.mcneel.com/labs/devsrf

    Rhino 6 has the DevLoft command. In some ways DevLoft is an improvement over DevSrf but it has the disadvantage of deviating from an exact developable surface when the corresponding ends of the edge curves do not lie on a untwisted ruling line. One way to use DevLoft is to extend the edge curves, determine an untwisted ruling line near the ends of the edge curves, trim/split the edged curves using the untwisted ruling line, and then use DevLoft with the revised edge curves. A method for determining exact untwisted ruling lines from edge curves is described at Developable surface - exact ruling lines from edge curves https://discourse.mcneel.com/t/developable-surface-exact-ruling-lines-from-edge-curves/73928

    Conical surfaces are developable, but not all developable surfaces are conical surfaces. The method shown in the link in the quote will create a series of conical surfaces based on the subdivision of the two edge curves. However the curvature of the individual conical surfaces will go to infinity at the apex, and there will be kinks between the adjoining conical surfaces. That method "works" in practice to obtain an approximate unrolled surface which may or may not be "close enough" for a given construction method and boatbuilder skill.
     
  12. Renaud Chile
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    Renaud Chile New Member

    That's right, there is a flat bottom and it complicates a bit but the idea of Bhnautika helps me a lot. Ideally I would like to do all the bow more or less curved. But I see that it's not easy.

    Bhnautika: do you generate the surface "by sections" or "sweeping on two rails"? Because with my version of Rhino (3.0 :(), your technique does not allow me to make a suitable developable surface (by sections), I must be satisfied with a simple surface ... but Rhino still develops it and I get this that I want...


    David :
    I understand : my old version of Rhino limits me a lot. The algorithms for generating developable surfaces and unfolding had to be improved during successive versions ...
     
  13. bhnautika
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    bhnautika Senior Member

    Renaud Chile I fired up an old computer and found rhino 2 so the results should be ok for R3 . used the two rail method for first chine, I added some extra straight intermediate lines down the hull between the small lines at bow and stern to hold the shape. Then the bottom was trimmed off to get the flat. All un-rolled in rhino 2, in fact better than R5.
     

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  14. Renaud Chile
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    Renaud Chile New Member

    Bhnautika, I do not know how to thank you! I did not understand the interest of the intermediate lines in the function "scan on two rails". I will back to Rhino's textbooks to see if other subtleties would have escaped me. I do not understand the difference between creating "sectional" surface and "two-rail" surface. Even if the mechanism is different, I have the impression that the result is the same ...
    Otherwise, you told me that Rhino 2 was better to unroll than R5? Surprising (Oulala!:rolleyes:)
    Anyway thank you, I think my problem is solved. :)
    Merci
    Renaud
     

  15. bhnautika
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    bhnautika Senior Member

    De rien
     
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