Mold from lines

Discussion in 'Boat Design' started by corkzak, Sep 24, 2013.

  1. corkzak
    Joined: Sep 2013
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    corkzak New Member

    Hello

    I have the lines for a st Lawrence skiff and the table of offset figures. The question I am asking is what lines do I use to work out the molds for the hull. Plus I have no idea what the offset figures mean as i am a complete novice. The lines have four sketches top side front and bottom view.
     
  2. DCockey
    Joined: Oct 2009
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    DCockey Senior Member

    Search for threads on "Lofting".

    Read the Chapter 16 on Lofting in The Gougeon Brothers on Boat Construction. It's available for free download at http://www.westsystem.com/ss/assets/HowTo-Publications/GougeonBook 061205.pdf

    Which St Lawrence River Skiff do you have lines and offsets for?

    Do you have any experience with building boats?

    What type of construction are you planning?
     
  3. bregalad
    Joined: Dec 2010
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    bregalad Senior Member

    You really need to find a tutorial on lofting. I believe several have been mentioned in threads here.... do a search.

    The offsets allow you to reproduce the 'lines' full size. I presume those are among the drawings you have. The idea is that as you fair the various slices of the hull (sections, waterlines, buttocks and perhaps some parts) full size you will find and correct errors that may be there in small scale drawings, where the thickness of a pencil line represents a significant fraction of an inch. In most cases computer generated lines and offsets would be more accurate.

    It should say somewhere whether the lines are to the inside or the outside of the planking. These days it's common that they would be to the outside of the planking. Not too many years ago some designers/builders drew plans to the inside of the planking. Pete Culler, for one, comes to mind.

    There is a thread on building a St. Lawrence Skiff skiff here:
    http://forum.woodenboat.com/showthread.php?123022-St-lawrence-river-skiff

    If you look at this picture http://farm6.static.flickr.com/5168/5322497305_c20991549e_z.jpg

    You want the molds to describe the shape at the juncture of the planking and the frames. The ribbands will go outside the molds and the frames will be bent to fit against the inside of the ribbands. Planking outside of that bringing you to the dimension describe by the lines and offset 'to the outside of the planking'.

    There can be some variations depending on the scheme the designer/builder had in mind. If you were to build the thing cold molded the battens/stringers around which you were planking might be outside the molds if they were going to be left in the boat, or let into the molds if you wanted to pop a clean hull off the plug. The mold dimensions would vary accordingly.
     
  4. corkzak
    Joined: Sep 2013
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    corkzak New Member

    I have no experience boat building. Have done woodwork and tech drawing. Will add some pictures of lines and skiff.
     
  5. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    It's not terribly difficult stuff, but it does take some understanding. You'd be best advised to get a few books on boat construction. The book store here is a great place to start.

    To answer your question, the stations seen the body plan would be useful, but frankly any of the primary lines can be used, such as the waterlines, diagonals or buttocks. Molds made to these dimensions (taken from the offset table) will define the hull's shapes.
     
  6. bregalad
    Joined: Dec 2010
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    bregalad Senior Member

    There's a book store here? Crap. There goes the budget.
     

  7. corkzak
    Joined: Sep 2013
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    Location: Norwich

    corkzak New Member

    Thank you for all your advice. I have downloaded the book and I am reading it now. Thank you all.
     
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