Any approved Naval Architecture software?

Discussion in 'Stability' started by Guillermo, Apr 26, 2008.

  1. MikeJohns
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    MikeJohns Senior Member

    I'm interested whether you get the discrepancies with tanks full and half full.
    ie is it a free surface calculation failure?

    Could replace the tanks with the equivalent heeled tank content as a fixed mass in the CG input and re-run and compare with the free surface in the same package. If there is a discrepancy then the software is out slightly with the free surface. You might want to ask whether the free surface is free to trim in both dimensions or just one.

    I suppose +-1 degree is accurate enough for most purposes. particularly when you know the boat will never be exactly to it's lines or COG. Just the bureaucrats get involved and them you cannot say.. "well that is reasonable enough".
     
    Last edited: May 2, 2008
  2. water addict
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    water addict Naval Architect

    Guillermo,
    regarding standards and stamping of approval, I don't think there is an official governing organization that has the power to grant any software as officially approved. There is no "Nav. Arch. Software Bureau" or some such that has the power to do that.

    I do know that if shcp stability computations are submitted to the U.S. Coast Guard, ABS, or the Navy and properly reviewed, the results will be taken to illustrate either adequate or inadequate hydrostatic properties.
     
  3. Javaid Hosany
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    Javaid Hosany Junior Member

  4. Guillermo
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    Guillermo Ingeniero Naval

    Mike,
    Not a problem of freesurfaces, I usually check that.

    Complying with the 25º exigency is mainly a matter of available freeboard. Trying to add ballast weight to solve the problem diminishes freeboard, so it's needed an extraordinary amount of it (because of the lost of freeboard with the increasing weight) just to correct some tenths of a degree, as said. Sometimes it's even necessary to rise the deck in combination with the adding of ballast, which is a major and expensive work.

    You're right on the bureaucrats thing: nowadays problem around here is we have had several stability related FV accidents in these last years, with the lost of many lives, so authorities have adopted a 'zero tolerance' policy (what is funny is if you work out GZ curves by hand you can easily make the curve to have its maximum at 25º -if difference is small- but you cannot do that if you use the computer's graphics and outputs. But they are insensitive to such reasons :rolleyes: ).

    Although these kind of problems are not new and have happened before, these days we are having an extraordinary amount of boatowners coming to the NAs offices asking to solve their boats' stability problems, because of the rigorous inspections that are being carried on.

    And when you play in the limits and you're trying to look for 'unpainful' solutions for the boatowner, then it's when you realize not all softwares are the same nor give same results.


    water addict,
    what I would like is that "Nav. Arch. Software Bureau" you mention to exist. In my opinion the professional tools we use in our work should comply with some mandatory standards, for our peace of mind.

    Cheers.
     
  5. fcfc
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    fcfc Senior Member

    I think you are searching the wrong thing.

    Approved software does not exist. For information, the most used design programs for cars and airline planes (near 100% of the market for big planes) is CATIA. And it does not carry any certification or approbation at all.

    If you look at aviation world, where certification is older and stricter, the only allowed measure is the real measure in real condition on the real thing. Any computer generated figure is just trash.

    Although Airbus has a bunch of megacomputers, and army of engineers, they had to break real wings of a A380 for certification test. See http://iagblog.blogspot.com/2006/02/airbus-a380-test-wing-breaks.html .It showed their FEM programs had a 3% error. Expect the same from Boeing http://blog.seattlepi.nwsource.com/aerospace/archives/115826.asp or even small kit aircraft manufacturers http://www.vansaircraft.com/public/rv-10int3.htm . None rely on computers figures.

    So, just build the boat, and measure the real stability of the boat, even if computer figures agree. Costly ? Yes. That is the price of certification/approbation.
    It will help solve the overfishing problem.
     
  6. Guillermo
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    Guillermo Ingeniero Naval

    How? Doing an stab test and then performing calculations the old way and drawing curves by hand? Is that more accurate than running a computer software?
    Or do you mean inclining each manufactured boat all the way down to 180º for every load condition, taking measures of the RMs at all angles?

    And this it's not a matter about FV only, but any kind of vessels.

    You're kidding, for sure. :)
     
  7. fcfc
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    fcfc Senior Member

    Unfortunately, I am not kidding.

    You have not looked carefully at the aviation certification process. They do a real wing test load for every load condition asked by the certification process. But they do it only on the prototype. Then they use certified materials, certified building technics, in a certified organization to ensure following production planes are as strictly as possible identical to the prototype which has passed real tests. This inludes also small private/club planes. That s why Cessna production falled from 17000 planes/year 40 years ago, before certification, to now 200 planes/year.

    For boating, it will be the same within a few years. I think you heard of a small polish built sailboat, that was CE marked by an Austrian company if I remember, that capsized in UK with fatalities, and when the actual boat which capsized was restested to CE/iso rules, the boat was found NOT compliant.

    So, if for stability, liability is real, the only real thing to do is a real inclining test with all load cases asked by the rule. It is not a joke, it is future.

    BTW, Open 60 sailboats, or recue boat do rerighting test in real life, not on computer simulation.

    Just doing a computer basic weigth estimation is hard to be correct, how can you imagine doing a computer stability curve for liability issues.

    What ensure you the hullform is as per plan. Speak of a mathematical NURB surface to a welder/grinder. With what tolerance on material. When you specify 6mm plate thickness, and the yard used or was delivered 6.35mm (1/4), you are already more than 5% off.

    The other very big point is the liability transfer.

    For now, the liable guy is the surveyor (or notified body) if his measure or computation is wrong.

    If there were "approved" software, the liability would be also on the software company. Then there should exists legal written rules to code software. That do exist for aircraft autopilot, instruments or engine control unit. You have skyrocketing price for software.

    Most common software, including windows or excel, are sold without ANY liability beyond software price for ANY purpose at all. Next thing would be the hardware on which the computer run. Remember of the Pentium division bug.
    If you need "approved" software, it can only run with "approved" operating system on "approved" hardware. You cannot have "approved" software that can run anywhere, in any conditions.

    If you try to find "approved" software, running with "approved" operating system, on "approved" hardware, you will see that the real inclining test for all load cases is cheaper.
     
  8. water addict
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    water addict Naval Architect

    Guillermo,
    It's not that computations or real tests are better or worse. For basic nav. arch. stability booklet type stuff, they go hand in hand.
    The static stability computations, as I'm sure you know, are pretty basic. Some center of gravity summations, volume, and inertia of the waterplane- pretty straightforward.
    So, you have a computer estimate of stability that gets verified by an inclining test.
    Most static stability software will come up with numbers that are damn close. The biggest thing to watch out for is input errors (user making a mistake), not software problems.

    The structural analysis verification that others have referred to is a bit more tricky. Inherent in the structural software (FEM approach) are assumptions on structural behavior which can be in error in real life. Further, the model maker has a much greater chance of really screwing something up, because there is so much more there to mess up.

    But for both, as always it's garbage in garbage out.

    Also wanted to mention regarding some governing body getting into software certification- this creates a set of real-world issues that can be unpalatable. If a government is doing this certification, then there are obvious political consequences that come along with it. "My software is better, and I'll give you $x.00 toward your campaign fund to have you certify it". And if history is any guide, this most assuredly would happen.
     
  9. Guillermo
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    Guillermo Ingeniero Naval

    That's precisely the point!
    May I add: "....and even if it is a software inaccuracy?"

    Perhaps most, but not all. As said, I've checked four and got four different results.

    Thanks to both of you for your posting.
    Cheers.
     
  10. SheetWise
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    SheetWise All Beach -- No Water.

    Guillermo --

    The government is not the answer -- you we're a lot closer to the correct path when you started. One way to take the liability issues out is to use the software developers own files. Each program comes with several sample design files -- if you take one sample from each program developer, you should get the same results on all programs. It will certainly point to the weak link -- and then you only have to publish the results.

    Edit - Reports from a test like this would have the added advantage of everyone developing sophisticated models that only their software could correctly calculate -- forcing competitors to revise features. It would raise the standards of all software.
     
  11. Guillermo
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    Guillermo Ingeniero Naval

    Thanks, sheetwise. Interesting idea.
    As probably hydrostatics will be the same, or very close one to the other, what is needed is to check KN curves for the different softwares. Also their results for lightship KG determination after an stability test (this last cannot be done with just the files from the software developers, as they are only simple hull forms. We need the real thing to this purpose).

    Cheers.
     
  12. NeiNastran
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    NeiNastran Junior Member

    The company I work for sells finite element analysis and design software for ship builders. My co-worker, Dave Buckman is a wealth of information on this subject matter. Feel free to contact him:

    Maritime/Offshore Industries
    Contact: Dave Buckman
    Phone: (714) 899-1220 x205
    Email: dave.buckman@noraneng.com
     
  13. Guillermo
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    Guillermo Ingeniero Naval

    But your company (Noran Engineering?) seems to have not any stability related software...:confused:

    I appreciate your kind offering, but I think it would be even more nice if Dave Buckman could post here by himself.

    All the best.
     
  14. SheetWise
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    SheetWise All Beach -- No Water.

    It seems to me this is an independent third-party offer. There is nothing of value to be gained from those in the business...
     

  15. Guillermo
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    Guillermo Ingeniero Naval

    Yeap. No one of them have showed up in this thread in spite of several stability software developing companies' people having showed around at the Software threads in many other ocasions. I wonder why....:)

    Cheers.
     
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