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Thread: lofting offsets, planking thickness reductions.

  1. #1
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    Default lofting offsets, planking thickness reductions.

    I've lofted a few boats at 1.5"=1' and I'm doing my second at full size.

    i have previously lofted the lines to the outside of the planking (the numbers as they show in the offsets) and then gone back to and marked the planking thickness and draw in a second Line at the framing edge

    this is is how I have understood it is supposed to be done. but my question is -

    could I subtract the thicknesses before I lay down my lines??

    ... it would seemingly save me some time and the headache of differentiating between tiny, crossed up pen lines. I can't imagine why this wouldn't work but I figured I should ask before I make a headache for myself

  2. #2
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    Default Re: lofting offsets, planking thickness reductions.

    You could subtract the thickness before laying down your lines... but you'd first have to know the thickness. And you must first do the lofting to determine that. Sort of a Catch 22.

    Jeff

  3. #3
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    Default Re: lofting offsets, planking thickness reductions.

    That's what I did. I took off an inch and a quarter from the lines on the floor, and built the molds.
    Later, the planking showed up, was inch and a half.
    My boat is quarter inch bigger EVERYWHERE.
    The world did not end.

  4. #4
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    Rockland Maine USA and Woodbridge, Suffolk, England
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    Default Re: lofting offsets, planking thickness reductions.

    Planking thickness on sections (like frames) is measured normal to (square to) the line of the outside of the hull that you lay off. So it's not a constant amount when measured horizontally (like on waterlines) or vertically (like on buttocks). So you can't easily deduct it before laying off.

    Cheers -- George
    To be truly free to live, one must be free to think and speak.

    A C Grayling

  5. #5
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    Default Re: lofting offsets, planking thickness reductions.

    Quote Originally Posted by telenorth View Post
    I've lofted a few boats at 1.5"=1' and I'm doing my second at full size.

    i have previously lofted the lines to the outside of the planking (the numbers as they show in the offsets) and then gone back to and marked the planking thickness and draw in a second Line at the framing edge

    this is is how I have understood it is supposed to be done. but my question is -

    could I subtract the thicknesses before I lay down my lines??

    ... it would seemingly save me some time and the headache of differentiating between tiny, crossed up pen lines. I can't imagine why this wouldn't work but I figured I should ask before I make a headache for myself

    what is the hull?

    I've got the feeling John Gardner has most of his offsets to the inside of the planking, on his dories anyway.


  6. #6
    Join Date
    Nov 2011
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    5,232

    Default Re: lofting offsets, planking thickness reductions.

    What will happen is you'll be changing the beam the same amount at each section perpendicular to the center line rather than perpendicular to the outer face of the hull at each point. Where the planking is vertical or close to it it won't make a noticeable difference, but down by the keel where the planking is closer to horizontal on a round bottomed hull it can make for some pretty big changes. Your traditional method is more accurate, tho still not absolutely perfect, and not all that much more work.

    I think you'll find that marking the second set of lines in a different color will be helpful. Another way to deal with it is to fair with a batten the same thickness as the planking and mark to the inside of the batten.

    If you're doing a straight sided or nearly straight sided dory like Daniel's where you have a flat bottom and constant deadrise you can deduct from the offsets and be just fine, tho once again, not perfect. Even then you will save time by using a straight edge the same thickness as the planking and marking to the inside of the straight edge.

    So, what are you considering building?

  7. #7
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    Default Re: lofting offsets, planking thickness reductions.

    Quote Originally Posted by wizbang 13 View Post
    That's what I did. I took off an inch and a quarter from the lines on the floor, and built the molds.
    Later, the planking showed up, was inch and a half.
    My boat is quarter inch bigger EVERYWHERE.
    The world did not end.
    That's what happened to me too (also by about a quarter inch)... but she hasn't quite hit the water yet so whether or not the world ends remains to be seen.

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