Offsets

Discussion in 'Software' started by wrabbit, Apr 14, 2006.

  1. wrabbit
    Joined: Apr 2006
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    wrabbit New Member

    Hi,
    I am using freeship as design software (www.freeship.org). I don't really understand how to use offsets to define a hull. Is there any beginners information on offsets?

    Thanks
     
  2. DanishBagger
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    DanishBagger Never Again

    Offsets are halfwidths from the centerline, and heights on those hlafwidths from a baseline.

    Chapelle's "Boatbuilding" has some good info on lofting (i.e. using offsets to define a hull, although not with a computer), there's a couple of other good books on the subject out there, "Lofting", but I can't remember the name of the author on that one (Valdez?).

    Edit: It's sort of an X/Y diagramme, where the x (horisontal) is the baseline, and y (vertical) is the center line.


    Andre
     
  3. DanishBagger
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    DanishBagger Never Again

    Ouch, I think I forgot to mention something rather important:

    Each station (a station is just a defined distance from the stem or transom of the boat), has it's own offsets, naturally, unless it's a pipe, and by defining the distance from the end, and then the distance from respectively the base line and the centerline you get a series of points you can then connect.

    I did it the analogue way, with bendable sticks, but it's the same idea.

    You have to subtract the thickness (scantlings) of the planks/glassfibre and so forth, though.
     
  4. Chris Ostlind

    Chris Ostlind Previous Member

    Here's the book to which the Bagger referred:
    http://tinyurl.com/rkwzr

    It's called: Lofting by Allan H. Vaitses

    Chris Ostlind
    Lunada Design
     

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  5. lewisboats
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    lewisboats Obsessed Member

    Offsets define the hull thru an X,Y,Z coordinate system. X is defined as your station points from the bow or stern along the DWL. Y is the height coordinate when looking at the profile and Z is the beam coordinate. The beam is expressed as a half width...it assumes that the hull is symmetrical along the centerline. You can also use this system for plotting the lines of a developed panel...tho usually you only use X and Y as the panel is assumed to by 2 dimensional. Stitch and glue uses this method extensively, as the panels are pre-shaped to give the correct shape to the hull.

    Steve
    Chris, you must type faster than me :D
     
  6. DanishBagger
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    DanishBagger Never Again


    Yup, that's the one :cool:
     
  7. wrabbit
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    wrabbit New Member

    thank you

    thank you all for your help in such a short time frame!!!!
     

  8. DanishBagger
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    DanishBagger Never Again

    You're welcome.

    As a p.s. I found it really funny lofting in real size. It's amazing. No "black art" to it as some will have you think, it's just a matter of being precise. To see the lines take shape from a few numbers is amazing. I think I could build another (simple) boat, just to have my fun with laying down the lines. I really enjoyed that part :)

    Good luck.
     
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