Offset Tables And Lines Drawings

Discussion in 'Boatbuilding' started by BASIL J WALL, Feb 20, 2012.

  1. BASIL J WALL
    Joined: Nov 2011
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    BASIL J WALL designer

    Hi..
    I just want some feedback from builders on the various continents...
    How do you use offset tables and lines drawings from the designer, when you build a boat?
    Do you set the lofting using the tables? Or do you measure from the lines and do your own lofting from them? What size of paper do you use to start this process?
    I'm setting up a single sheet with lines and offsets on the same page which can be printed on 2' x 3' paper...it looks very busy and I personally, would rather have as large a drawing as possible on one page and have the offset tables on a separate sheet...

    Thanks

    Basil Wall
     
  2. DCockey
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    DCockey Senior Member

    Related question: How many commercial builders today build directly from paper lines drawings and tables of offsets?
     
  3. jehardiman
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    jehardiman Senior Member

    All you need is the readable table of offsets. The lines will be lofted full size on the loft/building floor. Any inconsistancies will be taken out there. Really, it dosen't matter a 1/8th or a 1/4er here or there. This is even more pronounced in steel building, were a 1/4 gap can just be brought up with the dogs on the platten. Otherwise, this is carpentry, not cabinetry.
     
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  4. DavidJ
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    DavidJ Senior Member

    As a hobby builder I use just the offset table like jehardiman said. I fair out the inconsistencies on the loft floor and use the drawing as a guide to make sure I'm on track.

    However, as David Cockey was hinting at, in my professional career I have never once seen a table of offset made for any designs. I'm a naval architect with experience in both yacht and commercial design offices. I've never made a table of offsets and I've never heard anybody ask for one. The well equipped yards CNC cut everything themselves. The smaller yards outsource the CNC work to specialty companies. The cheapo yards print full size mylar templates.

    A lines plan is a fairly archaic drawing really. Since most designers start with a 3D model it is easier to just cut sections right out of the model and send them to a cutter.
     
  5. gonzo
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    gonzo Senior Member

    I always use the table of offsets. The drawing are just a representation to make it easier to visualize the design.
     
  6. jehardiman
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    jehardiman Senior Member

    That is only true in new construction with a single hand beginning to end, not in yard work. If you have to make a part so that it fits, you are going to lift the lines and loft the moulds and templates and maybe make a CNC file to do the actual cutting, but not if a field cut has to be made. I've never seen a CNC part made from a model fit a already existing structure without some trimming to shape. Even worse is trying to mate two parts modeled by two different 3D software (like CATIA and SolidEdge).
     
  7. Wynand N
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    Wynand N Retired Steelboatbuilder

    I never trusted CNC especially building a steel hull. If you off by a few mm somewhere, everything after that will not fit. Cutting plates etc yourself, you can correct yourself as you go along and save time.

    BTW, I had lofted every boat I had built in my career as boatbuilder.
     
  8. DCockey
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    DCockey Senior Member

    I visited a tug builder in Maine last autumn. They have all their steel cut and formed from the 3D digital model, not lines and offsets.

    On the other hand I wouldn't be surprised if in the last few years in Maine a mold for a lobsterboat hull was built from a half model.
     
  9. gonzo
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    gonzo Senior Member

    The 3D model that you see on the screen is a representation of the table of offsets (points) of the design.
     
  10. DCockey
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    DCockey Senior Member

    Could you elaborate? A boat can be designed without ever creating a traditional table of offsets. Such a table wouldn't exist, even in the software.
     
    Last edited: Feb 22, 2012
  11. gonzo
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    gonzo Senior Member

    It kind of self generates because you are creating lines between points.
     
  12. DCockey
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    DCockey Senior Member

    If you are refering to a "table of offsets" as the heights and widths at intersection of waterlines, buttocks and diagonals with the sections then it does not "self generate", not even "kind of" in software which works with surfaces, for example FreeShip, Rhino and MultiSurf.
     
  13. gonzo
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    gonzo Senior Member

    They way I understand it, the user defines points, which have an XYZ coordinate. Those coordinates are the same as a table offsets.
     
  14. DCockey
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    DCockey Senior Member

    Lots of different methodes to create hull surfaces in 3D software. Only a very few result in a set of coordinates corresponding to a "table of offsets". Some methods involve putting points which the hull surface will pass through, similar to a table of offsets, though for different sections may or may not fall on the same waterlines and buttocks. Other methods use control points which the hull does not pass through. Some use curves to control the surfaces while others develop surfaces directly.
     

  15. cthippo
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    cthippo Senior Member

    I'm going to be doing this process on Friday for a couple of new kayaks I've designed. I'm thinking about putting together some sort of illustrated tutorial since this question seems to come up a lot.
     
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