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Thread: Computer Hindered Design: Fairing lines with Excel

  1. #1
    Join Date
    Jul 2011
    Location
    Lindstrom, MN
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    2,059

    Default Computer Hindered Design: Fairing lines with Excel

    Rather that write a book, I am throwing this out to see if anyone is interested. The details could cure insomnia or drive you to distraction, so I will try to be brief.

    While it is not to be recommended as CAD software, Excel is more available to more people than anything else. Freeship and Hulls seem to do a lot, but they seem to alter the offsets more than I like. I can't really critique Hulls and Freeship because I have too little experience to claim any level of expertise.

    The reason for trying in the first place was to see if I could generate an accurate enough set of waterlines to get the offsets for a new set of stations that were closer together than the two foot spacing in Manley's book. After 40 years, I still have the stripper and am unlikely to build another one, but now and then I fiddle with the workbook in the wee hours. After many years and versions of Excel from DOS through windows 10, poking at a table of offsets I finally got from trend lines to workable equations. The trend line feature has improved over the years, but the trend line is still far from perfect, and it doesn't always come close enough to use.

    The offsets of the Rushton guideboat Station 4 as recorded by Orvo Markkula can be approximated with an equation tweaked from the trend line in an Excel graph:
    Station 4 -0.00017815*x4 + 0.0132*x3 - 0.3429*x2 + 4*x + 1.548 From x = 3/8 to 13
    x is the height above base in inches
    It compares well with the original offsets and smooths out some of the kinks:

    half breadths
    height calculated original difference
    0.375 3.000 3.000 0.000
    0.500 3.464 3.385 0.079
    0.938 5.007 4.731 0.277
    1.688 7.384 7.038 0.345
    2 8.279 8.000 0.279
    4 12.861 13.125 -0.264
    6 15.824 16.000 -0.176
    8 17.631 17.625 0.006
    10 18.677 18.625 0.052
    12 19.286 19.750 -0.464
    13 19.510 19.500 0.010
    The graphs do not end at the shear, so the weirdness on the right side isn't part of the boat. The equations don't work well if you don't extend the heights a little.
    Guideboat offsets.jpgGuideboat offsets from equations.jpg

    EDIT:
    I doubt too many non-insomniacs will be following this one too closely.
    Point taken. Not even going to bump this one. But you need 3D to work with a hull.
    From Dassault Systemes: DraftSight is a professional-grade 2D design and drafting solution that lets you create, edit, view and markup any kind of 2D drawing.
    Last edited by MN Dave; 12-21-2017 at 10:54 PM.
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  2. #2
    Join Date
    Jan 2004
    Location
    Norwich,United Kingdom
    Posts
    5,473

    Default Re: Computer Hindered Design: Fairing lines with Excel

    Given the availability of good,free CAD software I doubt too many non-insomniacs will be following this one too closely.Take a look at what Draft Sight can do its basically a clone of Autocad LT and is free for hobbyists.None of which detracts from the work done by the OP.

  3. #3
    Join Date
    Oct 2008
    Location
    Walney, near Cumbria UK
    Posts
    39,720

    Default Re: Computer Hindered Design: Fairing lines with Excel

    That is how I prepared the input files for my Freeship coble designs. Do a rough sketch on graph paper, put the knuckle lines through Exel and export the offsetts in the format required by Freeship. From there the design/fairing process is easy.
    It really is quite difficult to build an ugly wooden boat.

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