Semicircular hull shape in Freeship

Discussion in 'Software' started by Elgato, Dec 29, 2022.

  1. Elgato
    Joined: Dec 2022
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    Elgato Junior Member

    I intend to, and probably more than one model. But first I want to be able to design it, in Freeship or similar program.
     
  2. pafurijaz
    Joined: Dec 2016
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    Location: Jamestown, Saint Helena

    pafurijaz Senior Member

    I made this hull for you with FreeShip, I hope it will be useful in some way, you can inspect what I made, but the dimensions are probably wrong, but it can be useful as an example to inspect.



    Greetings
     

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  3. Elgato
    Joined: Dec 2022
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    Elgato Junior Member

    Thank you! Really appreciated. But I can't open the .fbm, it seems that my current version of Freeship (2.6) is too old. Which version do you use? There seem to be a lot of different versions available, is there any "latest"?
     
  4. pafurijaz
    Joined: Dec 2016
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    Location: Jamestown, Saint Helena

    pafurijaz Senior Member

    Hi here is a link I found a few weeks ago and it's the latest available in the internet Archive (https://web.archive.org/web/20161001193944/http://www.hydronship.net/download.htm)

    Direct link to the rar full with all applications <-- FREE!ship Plus : v3.5 - full - NEW -->

    upload_2023-1-28_15-15-4.png

    You can open also with a new version but is very buggy and many things are not complete but works yo open this file without versions problem and is the one still maintained and also available for Linux OS that I have.
    FreeShip+ 4Lazarus. Linux-x86_64, Windows-x64, 5.0.36-alpha Pre-release

    Feel free to ask a changes I can do this if you have a specif dimensions for this hull.
    Greetings!
     
  5. Elgato
    Joined: Dec 2022
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    Elgato Junior Member

    Thank you! Now I can open it. I now understand a little better I think, the points at the top half of the circle were moved horisontally to create the vertical freeboard, which can then be simplified by collapsing/deleting control points (as I did). I deconstructed your design in the front and rebuilt it with constant radius at each station using Extrude edges and then Move horisontally, and then moved those points that came to the wrong side to the midline. I guess some of those points could have been collapsed or deleted for simplicity. BUT it contains a lot of guessing and eyeballing how to position them to keep the constant radius all the way to the midline. Perhaps there exist some clever way to find the intersection with the midline in an easier way, but until then I will give up this attempt to CAD a semicurcular constant radius hull shape. I didn't bother to modify the aft of the boat and I destroyed the faces so no design hydrostatics ... it now looks terrible, sorry for that :) . Also I haven't tried yet to start from scratch with an empty sheet, but I will leave this attempt for now.
     

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  6. pafurijaz
    Joined: Dec 2016
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    Location: Jamestown, Saint Helena

    pafurijaz Senior Member

    Hi, I'm glad it was useful, I looked at your model quickly and I saw that there are some vertices that are displaced and not arranged in the middle, this creates leak zones and it is not possible to do the hydrostatic calculations.

    When simplifying you must absolutely avoid deleting vertices, because everything affects the result of surfaces and calculations. This program uses subdivision surfaces and surfaces should be whenever possible with a square topology.
    Subdivision quad topology Eg.
    [​IMG]
    [​IMG]
    With quad topology the surface are better. FreeShip use this type (subdivisions surface) at the end is mesh polygon modeller like Blender and other, it don't use NURBS, even if can export these into IGES!
    Interesting topic on hull design with SubD Surfaces:
    https://www.researchgate.net/project/Ship-hull-form-modeling-based-on-subdivision-surfaces

    I made the model following your sections as you can see from this image, and all section (station) with the same amount of vertex for a better topology, I think every was necessary.
    Station-cat.png

    I advise you if you don't know this tutorial for FreeShip, it could help you in the work.

    FREE!ship Tutorial - Forming the Hull http://www.hapby.v-nam.net/FREEship/FREEship-Tutorial0.html

    Greetings
     
  7. Elgato
    Joined: Dec 2022
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    Elgato Junior Member

    Hi, thanks, sorry, I didn't spend any time to make it leak free, but I know how to do it and I am aware of that great tutorial. Because my focus here was only to understand how to achieve a constant radius at all parts of the hull. Your model is close but not exactly what I wanted to achieve. A made a Paint sketch to illustrate: 1) at the stern, the flat horisontal section (marked light blue) is exactly horisontal, and goes to zero width at the midship station (and hence does not continue to the stem). All stations below this area should have exactly the same radius; the bottom curve in the upper yellow box should have the same curvature as the semicircular bottom = midship station curve. Whereas I think they are slightly flattened in your model. Likewise for the front part the forward station(s) (in the midship yellow box) should have exactly the same curvature as the (same!) outmost midship semicircular curve. I also notice that also your model has points (dark blue arrow) that looks manually positioned, no?
     

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  8. Elgato
    Joined: Dec 2022
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    Elgato Junior Member

    Here are Paint drawings, bottom and side view to clarify what I want to be able to create in FreeShip. Bold straight lines are completely straight, yellow and green areas have exactly the same single-bent curvature / radius (except for the longitudinal bent in the freeboard), yellow areas indicate that the curved areas sharply intersects with the flat bottom panel aft and the midline forward. Orange areas indicate the complex double-bending transition zones (that would be a challenge to build). White areas are completely flat. Easy and fast to sketch in Paint, very difficult and tedious to make in FreeShip it seems.
     

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  9. pafurijaz
    Joined: Dec 2016
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    Location: Jamestown, Saint Helena

    pafurijaz Senior Member

    This drawing helps to understand better than the previous one, try to guess how to do it, for information I will use Blender, and then I import the file into FreeShip via VRML V1, I create it with Blender because I'm used to working with that.


    Greetings.
     
  10. Elgato
    Joined: Dec 2022
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    Elgato Junior Member

    But of course, that is the way to do it! Since the shapes (except for the transition zones perhaps are simple cylindrical and rectangular blocks with intersections, creating the hull in CAD-programs such as Blender sounds like the smartest first step, and then import it to FreeShip for hydrodynamics etc. Thank you for your analysis and pointing me in the right direction!
     
  11. pafurijaz
    Joined: Dec 2016
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    Location: Jamestown, Saint Helena

    pafurijaz Senior Member

    Hi, I tried to redo the hull following your new instructions, however it's not easy to understand, because some things are confusing, such as the design of the stations.

    However I hope this new model is similar to what you have in mind and can be a starting point.

    New lines plan of new hull
    CAT-hul1_Linesplan.jpg

    The measurements are still at my discretion.
    Code:
    - Project               : CAT-hull
    - Designer              : Elgato
    - Created by            : pafurijaz
    
    - Length over all       : 3.589 m
    - Beam over all         : 0.358 m
    - Design draft          : 0.182 m
    
    I can't spend much time on this, so in the Zip file you will also find the Blender model, structured with all the reference drawings and other things that have been useful for me in designing this hull.

    Tree of the various groups in the Blender file
    Cat-hull_03.png

    Screenshot with the hull and reference images.
    Cat-hull_02.png

    Screenshot with the hull
    Cat-hull_01.png
    In case you want to try using Blender you will need a program that converts files into VRML 1 format, because this is the only way to import 3D files into FreeShip.

    I found a command line program, which allows you to convert the OBJ format (of Wavefront) exported from Blender to VRML1 and it is meshconv.
    For ease of use you must save it in the same directory where you have your OBJ files.
    This is the command I used to convert the model for FreeShip with meshconv.

    Code:
    meshconv -c wrl -vrmlver 1 CAT-hul1.obj
    
    For Windows they are the same at least I think they are, I haven't used Windows for too long and I don't remember anything,
    To export the file from Blender I set the export options with the -X Forward orientation.



    In Blender there are two export add-ons, in this case I used the older one (Wavefront (.obj) (legacy)

    These are the options used.
    OBJ-export.png

    I am experienced but for beginners it might be difficult at first, however I think a CAD type program like FreeCAD could be a solution to design but you will find other problems like using models with FreeShip.

    I hope it will be useful for you and give you a way to understand how to do what you want.




    Greetings
     

    Attached Files:

    Last edited: Feb 7, 2023
  12. pafurijaz
    Joined: Dec 2016
    Posts: 283
    Likes: 57, Points: 38, Legacy Rep: 18
    Location: Jamestown, Saint Helena

    pafurijaz Senior Member

    A better hull, with fine tweaking of control points and with my interpretation.

    CAT-hull-01.png

    CAT-hul1_Linesplan.jpg
    Greetings.
     

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  13. Elgato
    Joined: Dec 2022
    Posts: 17
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    Location: Sweden

    Elgato Junior Member

     

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  14. pafurijaz
    Joined: Dec 2016
    Posts: 283
    Likes: 57, Points: 38, Legacy Rep: 18
    Location: Jamestown, Saint Helena

    pafurijaz Senior Member

    Very well I recommend PolyCAD, which can import hulls of various formats and also in mesh, so you don't necessarily need to use FreeShip, and you are free to use other applications.
    The license is free there is a trial month but after that you have to request your personal license.
    Greetings.
     
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