Help with ABS Spreadsheet

Discussion in 'Software' started by Willallison, Feb 16, 2007.

  1. Willallison
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    Willallison Senior Member

    I'm in the process of writing a spreadsheet to cover the ABS rules for motor pleasure craft.
    The copy of the rules that I have - which appears to be the most recent available - is a draft version written in 2000.

    In determining the bottom pressure, there are a number of factors that must be determined from figures 8.1, 8.2, 8.3 - ie Vertical acceleration factors Fv1 & Fv2, and the design area factore Fd. There may be others as well, but I don't have it in front of me at the moment, so I'm doing this by memory....

    Apart from the fact that these figures are appallingly presented in the document, I would like to know if there's a numerical way of determining them - in other words a formula I can plug into excel, rather than having to refer to the original document each time.

    Can anyone help with this?

    Thanks as always!
     
  2. riggertroy
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    riggertroy Senior Member

  3. Willallison
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    Willallison Senior Member

    thanks Riggertroy - that is in fact the same document - the corrigenda that you refer to is just a few corrections to the orginal document.... but thanks nonetheless.
     
  4. SailDesign
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    SailDesign Old Phart! Stay upwind..

    Will,
    Look in the Excel help for the "IF" statement. You can string together IF statements to allow you a simple calculation for each part of the figure. Let me know (by PM) if you have trouble with that, and I'll be motre specific, but it shouldn't be too painful (the second time...)
    Steve
     
  5. Willallison
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    Willallison Senior Member

    Thanks Steve - I'm aware of the IF function - but somehow I got thru the 1st 35+ yrs of my life without excell, so it's all a bit of a catch up game for me. I'll be sure to let you know how I get on!:D
    You can only imagine my dismay when I worked a bit further thru the ABS rules to discover that almost the entire bloody thing is based on refering to figure x, y, z.... !!:rolleyes: :(
     
  6. SailDesign
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    SailDesign Old Phart! Stay upwind..

    Will,
    Most of ABS is "look at Fig. XYZ", or else it's "interpolate from table ABC". Fun stuff if you are geek enough to admit it (did I say that out loud?)
    You will get used to it, just in time to never have to do it again coz the spreadsheet will be finished.
    Steve
     
  7. Willallison
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    Willallison Senior Member

    You know, what really surprises me is the appalling quality of the document. I mean one of the graphs (figure 8.2 I think), is not only hand-drawn and hard to read.... its got bloody white-out on it where they made a mistake and corrected it!! Ok this is supposedly only a draft document, written in 2000, but I'll be blowed if I can find the final version.....
    And to give you the graphs, but not the formulae that they're based on... well that's just crap. I would have failed every exam I ever suffered thru if I'd done that.....
     
  8. MikeJohns
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    MikeJohns Senior Member

    Will
    A curve fitting program is useful to convert the graph back to a function. If the curves are well behaved even Excel can do this. Alternatively if you send me the data points I'll give you a function that'll be useable.

    I share your angst, many standards are appalling in their document quality as low res scans incorporated into a pdf. Some that we have paid for and downloaded have bordered on illegible.

    Cheers
     
  9. fcfc
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    fcfc Senior Member

    Beware x from aft, as in ISO. not like ABS


    Fv1 = SI(x<0,55;0,25+0,75*(x/0,55);SI(x<0,9;1;1+(0,5*(0,9-x)/0,1)))

    Fv2 = SI(x < 0,5;0,5;SI(x < 0,6;0,5+(x-0,5)*0,5;SI(x < 0,95;1;1-0,5*(x-0,95)/0,05)))

    SI = IF in french excel.

    No need to curve fitting.

    You need curve fitting for Fd ( Ad / Ar). In ISO, they give you the equation, but as Ar id not the same in ISO and ABS, you cannot use it for ABS ...


    BTW, I have found although they look similar, there is a bunch of silly little differences.
    As Lhull and Bmax for ABS, Lwl and Bchine for ISO, deadrise at LCG for ABS, deadrise forward 0.4Lwl for ISO etc etc ...
     
  10. fcfc
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    fcfc Senior Member

    BTW, Fv1 and Fv2 are not vertical acceleration. They are longitudinal correction for pressure. The forward end of a boat is likely to experience bigger loard that the rear. The acceleration factor is n in ABS and ncg in ISO and is speed dependant.
     
  11. Willallison
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    Willallison Senior Member

    Thanks guys - Steve was kind enough to both send me a curve fitting program and give me the resulting equation for Fd.....
     

  12. fcfc
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    fcfc Senior Member

    If you go one step further,
    coefficient k and k1 table 9A.1 are the same in ISO.

    The equation for

    x = l/b ISO = l/s ABS

    k ABS = k2 ISO = (0.271 x² + 0.910 x - 0.554) / (x² - 0.313 x + 1.351)

    k1 ABS = k3 ISO = (0.027 x² - 0.029 x + 0.011) / (x² - 1.463 x + 1.108)

    For Fd, I have approximated with a ugly stair function. If your panel thickness happens to be 10.3157 mm, you wont have it accurately machined, you will just put 1/2' panel.

    But beware of legal issues. For me ABS compliance is for fun, the legal one is ISO. But if the exact compliance per rules is 10.3157 mm and the plaintiff expert find it to be 10.3156 mm you may be in trouble even if this was not the cause of the problem.
     
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