first question hull curve

Discussion in 'Boatbuilding' started by umahunter, May 24, 2012.

  1. umahunter
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    umahunter Junior Member

    well ive been googling to no avail so i figured ided ask building a 14 40 jon boat and im wanting to know is there a formula or some technique to figure the curve on the front of the boat where the gunnel comes toward the center line so its identical on both sides do most just get something bendable bend it and draw a line or make some sort of template :?:
     
  2. PAR
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    PAR Yacht Designer/Builder

    I'm not sure I understand your question. If attempting to make a part fit the space, such as a casting platform or fore deck, then a template will do and is the wise way to go. In a perfect world you could template one side and flip it for the other side, but in reality, nothing is ever perfect, so you template both sides and the hole area, to insure a perfect fit. Maybe a better description of what you're trying to do/make and some photos.

    And Welcome Aboard . . .
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    Think he wants a lend of one of those splines NA's use to draw curves.
     
  4. PAR
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    PAR Yacht Designer/Builder

    Well a batten is easy enough to make . . .
     
  5. daiquiri
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    daiquiri Engineering and Design

    This is how I understand the question - Umahunter is trying to figure out how to draw the developed shape of the plates forming the hull walls, in particular towards the bow, where they bend inwards and upwards:

    [​IMG]

    Is that correct, umahunter?
     
  6. PAR
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    PAR Yacht Designer/Builder

    That's the problem Slavi, the question is undefined.
     
  7. umahunter
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    umahunter Junior Member

    correct the curve of the side wall to the bow in your example there is slight curve in toward the center line narrowing the bow from the transom so what im wondering is how to form the curve on the bottom of the hull that the sidewalls will follow i included a crude drawing sorry my paint skills are nill my boat will have a much skinnier bow for tight trails etc and also a pic of another boat simmaler to the shape im going for [​IMG] [​IMG]
     
  8. umahunter
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    umahunter Junior Member

    hmm

    anyone ???
     
  9. PAR
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    PAR Yacht Designer/Builder

    It would be more helpful if you told us what you're trying to do, rather than attempt to get specifics about things you're not describing very well.

    To get a curve on what, the computer screen, wood, aluminum, making a template of an existing part, what? If you want to draw a curve full size, say on a boat, a batten is the usual choice. If you want a duplicate of this curve in reverse or mirrored, then you'll need to template this battened shape, then flip it. There are other methods too, such as a joggle stick. What are you trying to do?
     
  10. umahunter
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    umahunter Junior Member

    im sorry im not a seasoned boat builder and dont know all the proper building terms so please bear with me im trying to describe the best i can. if you look at the examples ive provideed i am building a 14 ft long 40inch wide hull from 5052 aluminum it will be made from one sheet im trying to figure the best way to cut the curve on the front of the boat then after the sheet is broke will form the side walls and bottom of the hull this pic is what im trying to achive to equal curves that form the front of the boat [​IMG] im just wondering how to get two exact curve so it symetrical do people use bender board or some math formula etc ???
     
  11. PAR
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    PAR Yacht Designer/Builder

    We would use a batten then draw the curve through plotted points, per the plans or offsets table. With this in hand, you can do it directly on the work (not very easy) or make a template in stiff paper or light plywood (chip board, Masonite, what ever), which is then transferred to the work. As far as making the hull "fold" together in one piece, well now you're getting into "developed" panel shapes, which will require some software, so you can plot out the points or print out templates. I don't know of any hunting boats, garveys or other pointed end jon boats that are folded up from a single piece, particularly along curved forward sections. They are welded or riveted along a seam from developed shapes.
     
  12. Tungsten
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    Tungsten Senior Member

    draw a centerline mark out 1' increments then measure from centerline on each side

    just a guess as i don't understand your question.
     
  13. Gump
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    Gump Junior Member

    Assuming you don't have the aid of a CAD program, I would do it similar to sewing a fabric pattern shape.

    A flat boat like you have pictured should be thought of as 5 distinct patterns. Back, Bottom hull, side hull (left and right mirror) and top edge.

    Bottom and top are simple, mostly parallel flat patterns, each will describe the size and shape of the boat sides. The side patterns are then more complex patterns that must match the lengths of the top and bottom pattern edges. back pattern is usually a simple trapezoid defined by the top and bottom patterns and the boats height.

    My advice would be to lay out your top and bottom patterns in the shape you want, then measure the exact length of the edges where the side pattern will mate to. Lay out your side pattern in the shape you desire and adjust it so that its edges are the same length as the respective top and bottom pattern. There is no magic formula that will tell you how the actual flat shapes will look. You just have to approximate and adjust to the actual lengths.

    Get some kraft paper and make a small model.

    Did that help ?
     
  14. PAR
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    PAR Yacht Designer/Builder

    Gump, you're kidding right? You think we just guess at this stuff? These boats were designed long before CAD was available. I guess will just muddled through some how.
     

  15. Gump
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    Gump Junior Member

    Perhaps I should have included "or sliderule" in the sentence? I'm obviously a beginner to the boat building game as well. I would love a quick explanation how you would go about it?

    Just as an example in this case where you have a defined upper shape tapering to a lower shape. How would you go about designing the curved side panel that would fit?
     
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