Modeling full/long keel hulls with Rhino

Discussion in 'Software' started by Adam Persson, Jan 31, 2014.

  1. Adam Persson
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    Adam Persson Junior Member

    Hello,

    I am trying to model a traditional full/long keeled hull from a lines plan using Rhino. My general strategy is to model the hull and keel as separate surfaces and then use MatchSrf to join them. I have been able to model the hull (except for the bow section) with no particular issues by lofting the stations, and I have also been able to join the hull/keel surfaces.

    I do however have problems creating a fair and smooth keel surface from the keel "stations" (with Loft, NetworkSrf and Sweep2Rails).

    How would you model the keel section of this boat? Would it be better to model the keel and hull as a single surface?
    Also, how would one go about modeling the bow section?
    If my approach is completely wrong, how would you model a yacht like this?

    Linked is a file with all the curves I have used, missing the transom.
    https://www.dropbox.com/s/g730d3946fyo67d/Test_4_Haven_12_2.3dm

    Best regards,
    Adam Persson
     
  2. SukiSolo
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    SukiSolo Senior Member

    Hi Adam, Welcome to the Forum.

    I haven't looked at the file - yet. Have you lofted the keel vertically?, or along the hull ie fore/aft? Vertical may be better. As usual there are most times three or four ways to get a good result. It is also possible that the original lines have an unfairness in them. Something that 3D modelling can show up!. Creating and using the correct curves is the key. When you get there you will wonder why it took so long!. In fact using maybe finding the best way is just being open to accepting that there are several ways to get at the result you want.

    As for the bow area, usually lofting from a 'Point' (the foremost stem) usually gives a good result rather than trying to use ever decreasing sections. Another trick is to create a construction surface, that the desired one must be constrained tangentally to. Best for Network Surf command. Lofting using a 'Point' at the end is good if not best for canoe sterns.

    I believe you are correct modelling the keel separate from the hull. It is the best way to create a 2.4 Meter type hull for certain.
     
  3. Adam Persson
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    Adam Persson Junior Member

    Thank you, SukiSolo, I have indeed tried lofting the keel vertically, but as you can see from the attached file (lines plan is in the file as a background bitmap) the foremost part of the keel has a very organic shape, and I do not have enough curves accurately describe the shapes and transition to the hull. I do however have a lot of stations describing each keel section. I attached a screenshot showing the cross-section curves for the keel.

    The major problem is the transition from a rather large radius on the bottom edge of the keel along the forward and midship stations to a rather small radius at the aftmost section of the keel.

    I can not get Rhino to make a smooth continous transition between these two!
    All the curves are represented with degree 5 curves with the same amount of control points which should, if I understand everything correctly, simplify the lofting.

    As for the lofting to a point method, I will try this, thank you!
     

    Attached Files:

    Last edited: Jan 31, 2014
  4. rwatson
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    rwatson Senior Member

    I had some success with putting in the waterlines, splitting them with vertical surfaces, drawing the sections on the vertical surfaces, then using 'Surface from 2-3 lines' and/or 'Surface from a Network of curves'.

    The secret seems to be the amount of detail you put into the lines , to get decent looking surface developments.


    If this dropbox link works, you can download the file I played with

    https://www.dropbox.com/s/6yxwl2gjvrjevad/Test_4_HavenTrial.3dm
     

    Attached Files:

  5. Adam Persson
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    Adam Persson Junior Member

    I managed to create a smooth and nice keel surface by separating the keel into two sections lengthwise, and then lofting two separate surfaces, followed by blending the two together. The keel does have a "sharp" break in the middle, so this method seems rather natural.

    The rear lofting works very well with the "loose" option, but when I switch to tight, the loft fails in a peculiar manner. The end of the surface "reverses". All of the curves are of the same degree (5) and have the same point count (6). I have also tried to reverse the curve direction, but this has no effect!
    The first picture show the loft with the loose option, the second one shows the failed loft.

    Does anyone of you know how to rectify this problem?

    rwatson, interesting, I will have a look at your method!
     

    Attached Files:

  6. SukiSolo
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    SukiSolo Senior Member

    On the keel 'joint' to hull, I think Blend Surfaces might work. You can constrain the conditions at each face of the surface. Check also 'Bulge' in the Help file, I have used this when trying to get tangency and a controllable bump in a surface before now.

    I'll try and have a look at the shape a bit further, I've only got Rhino 4 on this box (Win2k) so I can't read it. 5 is on a newer box - Win 7, but kept as a near standalone for security reasons.
     
  7. pyrohamish
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    pyrohamish Naval Architect

  8. Hampus
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    Hampus Junior Member

    Try running diagonals through your stations and build your hull, all at once, using "surface from network of curves" on your stations and diagonals.
     
  9. rwatson
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    rwatson Senior Member

    Thats looking pretty good, I reckon.

    Running diagonals sounds like a good idea, but it might introduce some unwanted curves.

    Maybe Hampus could demonstrate the concept in a drawing.
     
  10. Hampus
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    Hampus Junior Member

    I'll try. I'm just a poor Yacht Design student, and as for Rhino I'm pretty much self taught. This is however the best way I've found for building a full keel hull. With fin keels and centerboards you can just loft the stations and add the keel afterwards.

    This is an ongoing project and the lines are by no means perfect, there's some strange things going on around the stern (look at the waterlines) and also some strange things around the bow. Naturally, the hull surface won't be perfect either, but I hope you get the idea. you can use the file to experiment by including or excluding stations and diagonals in your "Surface from network of curves" and see what happens. The diagonals used are laid out solely for the purpose of building the surface, they don't have anything to do with the diagonals that would be shown in the lines plan.

    If someone has a better way of doing this I'm all ears and eyes! :D

    /Hampus
     

    Attached Files:

  11. Adam Persson
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    Adam Persson Junior Member

    Hampus, that is definitely an interesting option, but so far, I have not been able to get a smooth transition from the rounded mid sections of the keel to the rather sharp aft edge of the keel when using NetworkSrf. Loft will however do a very nice and smooth transition, while also respecting the curves well.

    Below are screenshots of my work so far, I am rather pleased. The hull and keel are lofted from stations as two separate surfaces, and then joined. There are still some detail work left to get the transition nice on the forward part of the hull, where the keel tapers into the stem. The surfaces that I have now is good enough for the current task at hand, hydrostatic analysis.
     

    Attached Files:

  12. Hampus
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    Hampus Junior Member

    I know this is a rather old thread but this might help someone.

    If you have a set of lines and if you can live with trimmed surfaces you can "patch" a surface over your lines and trim around the edges (auto trim usually works well).
     

    Attached Files:

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  13. rwatson
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    rwatson Senior Member

    Thanks Mr H. I have never tried the autotrim. Its a good tip.

    Edit - Duhh - no wonder I have never tried it, its the default :(

    Its been working that way forever.


    I wonder when you would *not* use autotrim ?
     
    Last edited: May 5, 2014
  14. Hampus
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    Hampus Junior Member

    I find that autotrim works well when your curves are very exact, but if they are not sometimes the surface might end up on the wrong side of one or more of your edge curves. If that is the case autotrim won't work, nor will any other trim. In that case it works well to move your edge curves away from the surface and project them back on to it. Then you use the projected curves to trim saway the excess.
     

  15. bhnautika
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    bhnautika Senior Member

    It is possible to get some of these hull/keel shapes with just one surface that is easily edited.
     

    Attached Files:

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