Remodeling Hull

Discussion in 'Software' started by Botho, Oct 30, 2015.

  1. Botho
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    Botho Junior Member

    Hello everybody,

    a part of my bachelor thesis is the remodeling of a fishing shooner in Maxsurf.
    So far I think it looks OK. But i just can't manage to get the transom the way it is supposed to be. I have spent days trying to figure it out, but right now I am rather frustrated. So I hope someone here has the clue.

    The problem is that the original stern was round and very wide. As you can see on the picture "transom" waterline #8 is almost straight and not as convex as mine. It is impossible(at least for me) to make this waterline as straight as in the original plan. Especially because then all other waterlines will be totaly distrorted.

    I simply modeled the transom by triming the stern. But this way the stern is no longer round and has a very pronounced corner. Maybe there is a way to keep the stern round and still model the transom?

    If anybody could help me i would be very gratefull!

    Thanks, Botho
     

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  2. TANSL
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    TANSL Senior Member

    It is not possible to see in detail in thumbnails what happens in the stern but it occurs to me that you could trim the hull surfaces by an inclined cylindrical surface. I do not know if that's what you've done.
    On the other hand, is likely that surfaces generated with MaxSurf are similar, but not identical, to the original body lines of the ship. Check all thousand times because with Maxsurf it is very difficult to get the boat you want. If you need precision, do not rely on what appears, check it out somehow.
     
  3. PAR
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    PAR Yacht Designer/Builder

    Welcome to the forum.

    That's a classic shaped "counter stern" and the waterlines in particular, show precisely what is happening. The diagonals also show to a lesser degree, what's happening to the shapes in the stern of this boat. Essentially there's a bunch of twist in these after portions of the hull, especially in the garboard and broad strakes, where they go from nearly vertically to nearly horizontally oriented. I'm not much of a MaxSurf fan, but I'll bet you can manipulate the lines to mimic these with some fiddling.

    From what I'm seeing, you've not very closely matched on other waterlines either. For example, between station 12 and 13, you've removed quite a bit of belly in the WL 5, yet just below this WL, you've added quite a bit of belly to WL 4, between stations 14 and 16. These distortions will play havoc come time to fair her up, not to mention don't represent the actual hull form, you're attempting to mimic. It's all about "in the seat" time with these types of programs, eventually, you'll learn how to manipulate them to do what you want.
     
  4. gonzo
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    gonzo Senior Member

    The other major problem is aesthetic. The sheer will show a hard corner and a hump instead of a smooth transition. It is an art form to create a shape that looks good from every perspective. That modification will not work well unless you also modify the sheer profile. In turn, that will force you to modify the rest of the hull lines to make them flow harmoniously.
     
  5. TANSL
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    TANSL Senior Member

    Rhino file shows a great hull. The only thing I would change, I repeat, is the plane with which you try to define the transom. It is very clear that the transom is not a plane, therefore, I would replace it by a cylindrical inclined surface.
    As for the deck line on the side, as you have it in Rhino is perfect. You should not change anything. And anyway, if you change, you will NOT be forced to modify the rest of the hull lines.
    Besides all this, what you may not know is to what extent the hull in Rhino is equal or similar to drawings on paper.
     
  6. gonzo
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    gonzo Senior Member

    A cylindrical shape will produce a curve on the transom that is pronounced on the center. That is the opposite of what produces sweet lines. It should be an oval of an ellipse.
     
  7. Rurudyne
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    Rurudyne Senior Member

    ^ this

    Botho,

    I've also found, in my limited experience, that if you need more control points to help define the perimeter of the transom than you start with you'll need to extend these forward along the hull as lines or else the model gets a bit unfair around the juncture to the transom otherwise.

    Another option, of course, it to either have many, many cross lines on your oval/ellipse shape and once you've tilted and intersected it with the hull get rid of all of them that don't closely align to a matching control point on the hull. You might save the transom with most of the lines as a part to better play around with what lines get the best results.
     
  8. TANSL
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    TANSL Senior Member

    Of course, you're quite right and, in my opinion, is precisely that, to get an oval. What you see in the figure is much like an oval.
    The lines will be "sweet" or not, but not because of the oval.
     

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  9. PAR
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    PAR Yacht Designer/Builder

    Knowing this particular hull pretty well, the transom is actually a conical projection, a bit wider radius at the top than the bottom. It's not the most complex set of shapes these traditional counters employed, in fact an effort was made to ease its construction, which may have been a Chapelle idea, instead of the yacht's actual lines.
     
  10. TANSL
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    TANSL Senior Member

    Indeed, seeing the body lines was easy to think that the transom was not flat.
     
  11. DCockey
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    DCockey Senior Member

    Another way to create the curved transom in 3D surface modeling software such as Rhino would be to first extend the sides and bottom slightly past the transom location to a plane. Fair the sides and bottom. Create a surface with the shape of the transom which extends beyond the sides and bottom. Then trim the extended sides and bottom surface and transom surface with each other.
     
  12. TANSL
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    TANSL Senior Member

  13. Botho
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    Botho Junior Member

    Thanks for your replys!

    I already found out that the transom is not flat. PAR is right I also think its not cylindrical but slightly conical.

    However the creation of the transom is not the main problem. The main Problem is the modeling of the stern of the hull. As i said the waterline just below the sheerline runs parallel to it with very little convexity, if you project it, it ends somewhere several meters behind the stern. The second waterline under the sheer runs almost at a right angle into the centerline.

    I dont know how to tell my surface how to generate this "twist". When I create homogene stern lines the waterline just under the sheer will also be convex just like the lower ones.

    I'm sorry for the bad resolution of the pictures, at the moment I dont have access to better ones. I will try to bring up better ones soon.

    My hull for sure is not 100% identical to the original, I wonder how exactly do I have to match my lines to the original lines to be in a position were I can say that it is a replica? And then there is the point that I need to extend the sheer about 200mm verticaly to acommodate a more comfortable interior. (So it already is not a replica anymore?...)

    I managed to create a faired hull. Of course it differs in some areas from the original, especially the stern. Now the question I am asking myself is: How much effort should I put into creating an even more similar hull? Where do I stop?

    The fact that there is not one lines plan for this ship, but several which differ, especially in the stern, makes it even more difficult!
     
  14. Botho
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    Botho Junior Member

    I think it is important to understand that the shape of the transom is completely dependent on the shape of the hull. I think the builders quite actually made the same as we did in our programmes: they just cut of a part of the stern. In this case not with a plane but with a cylindrical or conical shape
     

  15. Botho
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    Botho Junior Member

    Hello rurudyne,

    I'm sorry I'm afraid i dont understand you. Are you referring to using several surfaces and then intersecting them, or overlapping several rows of control points??

    So far I only used one surface for the hull, the keel is modeled with another one and the transom and the sheerline is trimmed.
     
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