Building a jig from a hullform design

Discussion in 'Boatbuilding' started by tampablendie, Apr 14, 2010.

  1. tampablendie
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    tampablendie New Member

    Hey Guys,

    I'm new to boat building and this is my first post in the forum. My question is; "How do you design the jig for a particular hull design?"

    I have obtained the designs for a Cherub Ellway 5 in a Hullform file. First off I don't see any dimensions when I open the file, just lines and sections that go 1:1, 2:2, 3:3..... and so on.

    Assuming I can get the program to show dimensions, these are the external dimensions of the hull. I then have to adjust for the thickness of the hull (carbon fiber layers and foam layer), and then for the thickness of the longitudinal planks(terminology?), before I can then build the horizontal ribs(terminology?). All of which depends on the slope of the curve of the hull for any given point on that curve.

    How do you accomplish this so the hull comes out like the design?

    Thanks in advance for any advice.
     
  2. alan white
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    alan white Senior Member

  3. tampablendie
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    tampablendie New Member

    Thanks for the reply alan,

    That is not the design I will be working with, the Cherub is an open class and there are as many designs as there are boats. I am planning on using a male plug jig, as I have read that female molds are very time consuming and only really appropriate for large production runs where many boats will be made.

    So let me clarify my question a bit. Imagine you have the designs for the external dimensions of a boat hull. Now you need to figure out the dimensions of the pieces to build a male jig that will result in the external hull shape you have.
     
  4. alan white
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    alan white Senior Member

    I wasn't familiar with the Cherub, that it was an open class. I put up the link for easy reference.

    I'm sorry but my approach would not be to use a software program. I would loft the exterior surfaces according to the plan offsets and then draw lines inside of those to the thickness of the hull and pick those up.
    If the hull isn't too thick, this would be pretty accurate. Otherwise, you might also draw the waterlines to be more precise.
     
  5. tampablendie
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    tampablendie New Member

    ok I'm following you here, so it should be accurate enough even though the hull is curved and the slope of the curve changes? I will be using the foam sandwich technique will the hull be too thick for accuracy here?

    If you could also take the example you listed above, and outline the steps to take that drawing all the way to a complete boat I would really appreciate the insight as to how someone who has done this before would proceed. The designs I have are similar to those pictures but have been numbered in sections.

    Thanks a lot and sorry for the noob questions
     

  6. alan white
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    alan white Senior Member

    The foam shouldn't be so thick that small angular changes would change the dimensions much at all. It isn't a large boat, so I imagine the hull wouldn't be more than 3/4". How exacting are you trying to be?
    Your layup alone is going to be inconsistant enough to negate any gain in accuracy. The only way to be close to perfect would be to use a female mold. I don't think the inaccuracy would exceed an eighth inch anywhere, and mostly at points of extreme curvature.
     
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