Delftship station spacing and chine plot

Discussion in 'Software' started by stevee, Jan 3, 2015.

  1. stevee
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    stevee Junior Member

    This must be a common question. Is it possible to place stations for the SURFACES of a chine boat at predetermined points. The control curve positions can be fixed externally, but what about the recovered station XYZ values. And is there any way to force the control curves of a chine boat to lie on the surface. There seems little point in entering the offset table if it generates the control curves and not the actual hull, nor can I see any way to see the HULL values in real time. All you get is the control curve. And for a round hull, is there any way of seeing the hull values in real time? Or am I missing something. Many Thanks
     
  2. TANSL
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    TANSL Senior Member

    It occurs in many programs, it is almost impossible to pass the surfaces exactly by points defined on the table of offsets. They create control points and a fit points and you can not make both sets of points coincide. So, after much work you get a surface that resembles the hull but that is not the hull. When it comes to a new project that perhaps does not matter. But when it comes to reproduce the shapes of an existing ship, it is a very serious problem. Because besides, it is not possible to know the degree of inaccuracy of the created surface.
    I offer you the possibility of using my ARQN software, which does not have these problems, to create surfaces that exported in DXF or igs format, could be used with the program that you like the better. Only need to see your table of offsets to know what colud be done.
     
  3. DCockey
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    DCockey Senior Member

    The ability to create a 3D model of a hull which matches a table of offsets or other specified points depends on the software. Rhino, for example has the ability to easily create curves which pass through a set of specified points. Surfaces can be created from those curves. It is also possible in Rhino, though not quite as easy, to directly create a surface which passes though a set of specified points. Also Rhino has a simple command which calculates the deviation between a set of points and a curve or surface.

    It has been a while since I tried DelftShip. My recollection, possibly incorrect, is there was not a way to have a surface pass through specified points.
     
  4. stevee
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    stevee Junior Member

    Rhino

    Thanks fot the above. Do you know if Rhino fairs curves and surfaces, and if it will tell you if a surface is developable? Also, a thought. On a chine hull, does fairing a critical curve, ie sheer, chine, and fairbody, automatically align the surface with the control curve? After all, fairing the control curve on hull line which is a simple concave curve may make hull and control coincident if there is no other deviation required by an inflection point?
     
    Last edited: Jan 4, 2015
  5. DCockey
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    DCockey Senior Member

    Rhino has tools for fairing and smoothing curves and surfaces including commands which will attempt to fair a curve or smooth a curve or surface "automaticially". Frequently the best way to fair a curve or surface in Rhino is to look at he corresponding curvature comb(s), surface zebra pattern or "fluorescent lamp" reflection, and move control points as needed. Rhino has also has tools to evaluate if a surface is developable including display of Gaussian curvature and area change when a surface is unrolled. Rhino should be thought of as a set of powerful tools and a work environment for designing 3D objects. It is not a program which will guide a novice in the "design" of a boat.

    Rhino can be downloaded free for 90 days use with no restrictions. http://www.rhino3d.com/download Plan to spend time learning to use Rhino before it becomes an efficient tool for boat design.
     
  6. DCockey
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    DCockey Senior Member

    Control points in general do not coincide with a curve or surface, whether the curve or surface is "fair" or not. There are special cases where they do such as at the ends of curves or where a curve is straight or a surface is planar.
     
  7. lewisboats
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    lewisboats Obsessed Member

    To see the surface values in real time export the offsets. File, export, offsets. This will give you the values at the stations you select under Calculations, Intersections and will also give you coordinates for the control curves. If the boat has chines, the chine intersections will be "Knuckles". The way to read it is from bottom centerline, up and around to the shear or the highest point the station crosses.

    Here is a picture of a single station at midships of MJ:

    [​IMG]

    When I export offsets {seen here}:

    [​IMG]

    You get a number of points. Some of these are for hidden layers, so ignore them. The one I want is highlighted. This is the Keel/Garboard Strake intersecting line or the Beard line. The position of the station is at 9.35 ft forward of the aft perpendicular (which is the 0 in this design) and the segment showing the straight keel is segment 3. The first knuckle is the centerline of the keel at the lowest point above the baseline. Next knuckle is the outer edge of the keel at the same height, then the highlighted one is the Beard line. The next is the intersection of the Garboard and the first side strake... etc.
     
  8. lewisboats
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    lewisboats Obsessed Member

    For a round hull things are similar except there are no knuckles except for sharp corners such as the keel area. Here is a picture of the same station with the chines uncreased, creating a round hull.

    [​IMG]

    and here are the offsets for the station:

    [​IMG] [​IMG]

    As you can see... the keel is still Knuckles but the rounded hull is simply offsets at a number of points along the curve of the side surface. They are read the same: Length from perpendicular, Width from centerline and then Height above baseline. What determines the spacing I don't know. None of them correspond to the same lines in the chined version except the shear which is a hard line and shows up as a knuckle.
     
  9. TANSL
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    TANSL Senior Member

    Steve, I probably have not understood anything but let me ask you, how can all this be related to the question asked by stevee in post #1?
     
  10. lewisboats
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    lewisboats Obsessed Member

    I though I was telling him how to see things in "real time" or as close as possible as far as the chines and round hull points. Having no experience importing offsets, I don't know if they generate control lines directly or generate points on the hull which then are used to extrapolate the control lines. Perhaps I misinterpreted or misread his post which had to me, multiple questions. While unable to answer all of them, I essayed to supply some information on some of them.
     
  11. TANSL
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    TANSL Senior Member

    Probably you are right and I have not understood. I thought that as the control points do not coincide with the points of the surface, stevee wanted to know how to view real-time points of the hull (surface) no control points of the surface, which are different things.
    My apologies if I'm wrong.
     
  12. lewisboats
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    lewisboats Obsessed Member

    I showed him how to get the real time points on the surface. The control points are something different. The output of the export offsets function is to give the points where the various intersections (Stations, waterlines, Buttocks or Diagonals) meet with the hull surface. In addition...it also provides offsets for the control curve. Each one of the points shown in the above txt file excerpts in "section 3" are coordinates for a point on the surface of the model, not the control point or the control line. Plotting those points on a lofting floor and either using a straight edge for the chined version or springing a batten on the round version will give you a section of the actual hull. However... it could be the inside or the outside surface because the model does not provide a thickness for the surface. You would have to decide to which surface you are designing to and extrapolate the other surface using your scantlings... which would have a small effect on the displacement of the hull if you choose to use the surface as the inner. However... it makes it fairly easy to design bulkheads or frames without having to subtract hull thickness when determining the outer dimensions of these items.
     
  13. TANSL
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    TANSL Senior Member

    I think, humbly, to show the points of (on) the surface is not possible.
    Another question, since you raised it : for ships, allways, body lines and therefore forms surfaces are inside the hull. You can put them where you want but if you do as I say, you will avoid a lot of problems.

    Mold Construction: when the hull is constructed by female mold, the lines are drawn on the outside of the hull (inside the mold).
     
    Last edited: Jan 5, 2015
  14. lewisboats
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    lewisboats Obsessed Member

    How would the program be able to unfold the flat panels of a chined boat if it could not represent the surface? If it can represent the surface, then why not be able to calculate a point on that surface that is the intersection of certain defined planes. I can pick a point defined in the .txt and place my cursor on that point on the surface of the model in the program. My only limiting factor in getting the point spot on is how fine in definition I can move my mouse. Zooming in on the model I can get it pretty much dead on as the mouse movements are incrementally smaller in relation to the surface. I note that my cursor is nowhere near any control lines but apparently dead on the surface of the model. As I am building an almost 19 foot boat using this program as the sole designing engine... I sure hope I can trust the mathematics that can produce a .0001 of a foot or 12/1000 of an inch increment of movement on the model.
     

  15. TANSL
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    TANSL Senior Member

    I did not say anywhere that it can not represent the surface. What I said and I repeat is that the points on the surface can not be represented. Can represent the intersection points of the lines used to generate the surfaces.
    I think you are exaggerating when working with such precision. From my experience I can tell you that there's no need much accuracy. Are you wasting time and energy. And another tip, if you can not point your mouse the exact point you want, you are taking a major problem.
    But I think all this the OP will care a damn, so I'll finish, for my part in this discussion. It was a nice experience sharing.
    Cheers.
     
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