Diagonals on Body Plans

Discussion in 'Boat Design' started by welder/fitter, Jan 26, 2010.

  1. welder/fitter
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    welder/fitter Senior Member

    As I work on my CAD, I am reading through several books on design and designing a 39' CC ketch, as an "extra-curricular exercise".

    I am having some challenges in educating myself on the positioning of the diagonals, on my body plan. The only book I have which clearly discusses placement of diagonals is Chapelle's "Yacht Designing & Planning", wherein, he seems to be saying that there is no hard/fast rule regarding placement, other than the diagonals passing through the most sections possible & not interfering with buttocks lines. Have I got this right? Any suggestions on placement? Thanks, in advance, for any/all advice.
    Mike
     
  2. jehardiman
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    jehardiman Senior Member

  3. welder/fitter
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    welder/fitter Senior Member

    Perfect, thanks! I should have searched "diagonals", instead of "body plan" (thought I did but, obviously, not well enough).
    I was going to pull the post, in case some designers got the wrong idea, but I figured it'd take my instructor a couple/few days to find the e-mail among the many he receives, & respond. Not that I'm in a hurry, but when one wants to know something...
    Much appreciated!
    Mike
     
  4. gonzo
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    gonzo Senior Member

    Diagonals are used to fair the hull at other than the horizontal and veritcal planes. There is no exact rule about their placement. For example, in the bow flare the diagonal may run from the tip of the bow stem at and slight slope downward and a plane of about 75 degrees.
     
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  5. Steve W
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    Steve W Senior Member

    As others have said ,no hard and fast rules for placement,what you are trying to do with the diagonals is intersect the skin at as close to right angles as possible on as many sections as possible in the areas where the waterlines and buttocks meet the skin at too much of an angle to get accurate mesurements to develop the shape.
    Steve.
     
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  6. Scott Carter
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    Scott Carter Senior Member

    One thing to remember is that diagonals don't have to be parallel to one another. If they are then you only have to give their angle once, but if they're not then you just have to indicate each angle separately. The importance of them being as close to perpendicular to a section as possible comes in the accuracy of measuring them and then reproducing them on the loft floor. There is inherently less error in measuring a segment whose end point is very definite.
     
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  7. welder/fitter
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    welder/fitter Senior Member

    Gonzo, Steve & Scott,
    Thanks, guys, your added info. has made everything crystal clear! I understood the benefit of diagonals, from working from plans, previously, but couldn't understand how they related to a specific point or line.
    Mike
     
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