Argh. How to add bow flare?

Discussion in 'Software' started by adt2, Dec 13, 2011.

  1. adt2
    Joined: Sep 2009
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    adt2 Senior Member

    I have a very simple plan for a flat-bottom skiff I'd like to build with my son. I'd like to add a little bit of flare to the bow, but I can't seem to figure it out in Rhino. Can somebody point me in the right direction?

    The model is very simple: a sheer, a chine, a transom, and a flat bottom. I just can't quite figure how to "pinch in" the hull just aft of where the stem will eventually be.
     

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  2. Joe Petrich
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    Joe Petrich Designer

    Actually you do have straight line flare in the bow because your lower chine is inboard of your upper chine. It looks like this boat will be built of plywood, in which case that's about all the flare you can expect without splitting the topsides into two strakes.
     
  3. DCockey
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    DCockey Senior Member

    Not sure exactly what your question is.

    I assume you will use plywood for the sides in which case the surface needs to be developable, which your design is, though the. This limits the shape somewhat. These limitations can be relaxed by extending the sides the chine and/or sheer. The surface developed using the extended curves, and then the surface trimmed.

    I modified your design (see attached) by pulling in the chine aft of the bow by moving control points, then extending the chine past the bow. The ruling lines and surface now extend past the bow. The surface was trimmed back. Notice that the stem is no longer straight. This is due to the ruling lines crossing the stem. Shape of the stem can be controlled (somewhat) by the shape of the chine extension.
     

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  4. adt2
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    adt2 Senior Member

    I'll take a look when I get back to my office. Thanks for the input. In the meantime I can say that I am planning to strip-build the top sides and cross plank the bottom; no plywood. Seems like last time I tried to figure this out I needed to add another curve between the sheer and chine, but I might be imagining that.
     
  5. yipster
    Joined: Oct 2002
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    yipster designer

    hmm.. made me draw a new 5 min quicky with some more bow flair and a split forefoot in freeship
    its devellopable but should be better prepared in rite size with a stern and plate lay-out
    than -why did i?- to rhino and guess this is more what you mean, draw it the way you want it !
     

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  6. CmbtntDzgnr
    Joined: Jun 2011
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    CmbtntDzgnr Senior Member

    Wish I could help. Not sure if my own process (not related to Rhino) will offer any clues or workarounds.

    I don't think I have anything that'll import 3dm on my work computer nor my laptop with me.

    I could swear that PolyCAD imported .3dm. Maybe sketchup will. But, I want to see the bow flare.

    In my case, I created bow flare in Freeship, then exported my model to DXF and to .geo. But, once in PolyCAD, I could not easily get the flare and body curve right in a few tight areas. So, my attempt to resolve it was to add more and more and more stations. After a week or more of that, I gave up.

    Inside PolyCAD, I created bspline curves to match the dxf mesh stations paths at intersections along the waterlines and other areas as needed. Then, I dumped the surfaces and moved the model to Punch! ViaCAD (where I do my CAD detailing).


    Then, in ViaCAD I that rid of lots of control points in the polylines that made my surfaces multi rectangular. I then re-built the surfaces using the polylines converted
    to control point bsplines.

    A lot of hoops jumping.

    But, I'll eventually get around to using X-Topology as in the videos to deal with bow flare.

    I would have thoough Rhino to be capable of that.
     
  7. adt2
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    adt2 Senior Member

    Um...what?

    Maybe I need to ask a more specific question. It looks to me like what I need is a third longitudinal (fore-n-aft) curve about halfway between the sheer and the chine. I think by using the control points on that curve I could pull it in a little in the forefoot area to create the flared bow at the top (I don't want to move the existing sheer; I want to pinch in the hull below it to make it appear flared).

    So then my question becomes: How do I "split" the existing surface between sheer and chine lengthwise so I get a new curve in the middle? Or is that the wrong way to go about it?
     
  8. yipster
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    yipster designer

    think so Adt2, thought a half split in the bottom looks better and brings the bow chine up and more flair from flat panel is possible, takes some clamps but dont see a problem there
    by making a extra split in the bows side as you sggest, srry mobile typing pc off, I have to think, devellopable you wont get convex or co.ncave shapes and tryout I just did in freeship 3.2 ruvt showed no need..
    Not rhimo champ yet but try that tomorow if question is stillopen, basicly more flair shouldnt be to hard whatever prog used, just push and pull the lines and check devolapebility, srry for typos from mobil
     
  9. DCockey
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    DCockey Senior Member

    Several ways to create the side surfaces with more control of the shape of the side surfaces in Rhino when the surfaces don't have to be developable.
    1) Add a third curve between the sheer and chine. Use Loft with the Normal or Tight style option.
    2) Add section curves at the transom, stem and mid-way along the sides. Use Sweep2 with the sheer and chine as rails and the sections as sections to create the surface. Can add as many section curves as desired, but more section curves make it more difficult to get a surface with out lumps.
    3) Add section curves at the transom, stem and mid-way along the sides. Use NetworkSrf to create the surface. Can add as many section curves as desired, but more section curves make it more difficult to get a surface with out lumps.
    4) Add a curve between the sheer and chine and section curves at the transom, stem and mid-way along the sides. Use NetworkSrf to create the surface. Best if the curves intersect though a surface will usually be formed if they don't. Can add as many section curves as desired, but more section curves make it more difficult to get a surface with out lumps.

    All of these result in a single surface. In general it's best to use the fewest curves with the least number of control points which will result in the desired surface. If the surface needs modifying it's frequently better to go back, modify the curves and create new surface than to try to edit the control points of the surface.
     
  10. DCockey
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    DCockey Senior Member

    Simpliest method for your example is to use ExtractIsocurve. If the Isocurves are not running in the correct direction then use the Direction toggle in that command to swap direction.
     
  11. DCockey
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    DCockey Senior Member

    Follow-up to my earlier post.

    Simpliest way to control whether the sections are straight, convex or concave is to add sections between the chine and sheer, and then use either Sweep2 or NetworkSrf to generate the surface. For a hard-chine shape like you are designing the sections can have no more than 5 control points, and typically 3 or 4 are sufficient. Best if every section has the same number of control points.
     
  12. adt2
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    adt2 Senior Member

    Okay, maybe that wasn't what I wanted after all. I followed your advice and now have a nice new curve running fore-n-aft between the sheer and the chine. I displayed control points and nudged them in just a hair in the bow, but now I can't figure out how to get a new surface through the three curves. Grrrr.

    EDIT: Whoop, never mind. After nudging the curve in a bit, if I use Loft and select sheer+new curve+chine (instead of Sweep 2 Rails) I get the desired effect. Now it appears to be just a matter of noodling with the curve until I like the look of it. I'm attaching the new version in case anyone has further suggestion for improvement.

    Thanks for all your help.
     

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  13. Joe Petrich
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    Joe Petrich Designer

    You can try taking your single surface and rebuilding it to 3 points in the vertical direction (degree should be 2) and 5-7 points in the fore and aft direction with the degree set to between 3 and 5. Then manipulate the surface points to get the curvature you want. You must be careful in the movement of the points but you can end up with a very nice surface with reduced point count/complexity. It's just another method you may want to try.
     

  14. yipster
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    yipster designer

    thx guy's, will try your grips in rhino, exellent program yet another thought may be to try and use freeship for the skif
    delft/freeship is more specific to the job, trying out diffrent flairs a jiffy, does plating, calcs and more
    freeship is free and learned in a few days here's the old short manual
     
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