Software for tortured ply hull panels?

Discussion in 'Software' started by jamez, Feb 11, 2008.

  1. jamez
    Joined: Feb 2007
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    jamez Senior Member

    Hi, Just wondering if anyone knows of software that enables a round bilge hull form to be designed that will also plot the correct shape of the side panels on the flat (a bit like plyboats and others do for chine hulls)?
     
  2. Landlubber
    Joined: Jun 2007
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    Landlubber Senior Member

    jamez,

    Basically plywood can only be bent in one direction, the use of situations, as you have correctly called them, tortured, is actually very limited, and should be avoided as much as possible. This is not saying do not do it, but be aware that the stresses involved are not necessarily removed because it is fastened. It is better to design so that tortured (meaning forced into shape for those that are not aware) sections are at a minimim. I would not ever suggest that we should try to design a boat actually using tortured ply as a means, it is only to be used in specific sections that have " no other way".

    Now let the laminators have a go........they are right of course, you can do a small laminated section where tortured ply would have been used.
     
  3. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    You can build a round bilge hull form with sheet goods, like plywood. The trick is to rip the sheets into smaller widths, such as 6", but this depends on the amount of compound in the hull area being planked. The strips are then placed on the hull at an angle to the centerline, usually about 30 degrees or so, again depending on the amount of compound and radius conformation required for that section.

    The several molded building methods and Ashcroft planking use this concept.

    You can also reliably torture plywood into specific shapes, though I only have general radius guides, not compound curves. Much of it is a "feel" thing. After you've broken a number of panels you get an idea as to how much you can ask, before trouble bites your butt.

    PlyBoats used cylindrical and conically developed panels, which is a different animal all together. With "developed" panels you can ask a computer to "un-fold" the hull shape to flat panels, often with the ability to generate a "cut file" for CNC efforts. With a combination of developed panels and radiused "soft" chines, you can have much the same appearance of a round bilge boat, which is commonly done on metal boats, to make them appear round.
     
  4. ludesign
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    ludesign Senior Member

    As mentioned, plywood only allows one bending direction at the time. TouchCAD allows you to "laminate" strips of material in layers and in crossing directions, all to generate something close to a true compound surface.
     
  5. elliott
    Joined: Jan 2008
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    elliott Junior Member

    Hi Jamez ~ I am looking for the same type of program ~ and have had no success so far. My use is different from yours in that I am trying to get a computer generated multi-chined surface for a male mould made of flat sheets (following the layup of the inner skin and foam sandwich filler, the chines would be sanded round to give a double curvature on the outside).

    But thats another story.

    In theory there should be no problem in writing a program that allows you to model a flat unstretchable surface into a truncated cone (which is what you are after) but the big software programs have ignored this basic requirement due to them having their eye on the big bucks and not bothering with the small boat fraternity.

    Their excuse is that they have a system of 'developable surfaces' which does this but it is longwinded and clunky and ends up with approximations. I shall continue my search and will let you know if I find one. I have come close recently.

    In the meantime, I would play about with a half-hull model and bits of either cardboard or very thin ply (1.5mm). You should get a feel of what you can do and see where to go. Good luck.

    Cheers
    Elliott
     
  6. elliott
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    elliott Junior Member

    hi Jamez
    ref my last para, delete the bit about half model and substitute: cut out two identical sides with a keel profile that looks about right, lace them together along the keel line and then jam in some transverse bulkheads to get the shape you need. You will soon see just what you can achieve.
    cheers
    elliott
     

  7. jamez
    Joined: Feb 2007
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    jamez Senior Member

    Thanks all, for the various responses. Elliot, I've read the Gougeon book on the subject but was hoping to get away from the scale model system if possible......Not to worry, they don't call it eyball boatbuilding for nothing:).

    Its not just for Tornados either. Here is a picture of a 32 foot Malcolm Tennant designed tortured ply cat.
     

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