Maxsurf stability problem

Discussion in 'Stability' started by sn1987, Mar 19, 2016.

  1. sn1987
    Joined: Mar 2016
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    sn1987 Junior Member

    Hello to everybody,
    I'm new on the forum. I'm trying to calculate with maxsurf stability the boat's Hydrostatics but i have a problem. After I had defined the draft range the calculation start but at the lower immersion the value of KMt seem to be negative:confused:
    below are enclosed such results. Could it be associated to an incorrect trimmed surface?
    Thanks a lot guys

    Displacement t 8,548
    Heel deg 0,0
    Draft at FP m 0,500
    Draft at AP m 0,500
    Draft at LCF m 0,500
    Trim (+ve by stern) m 0,000
    WL Length m 11,491
    Beam max extents on WL m 0,542
    Wetted Area m^2 172,654
    Waterpl. Area m^2 6,429
    Prismatic coeff. (Cp) 5,051
    Block coeff. (Cb) 4,536
    Midship Sect. area coeff. (Cm) 0,898
    Waterpl. area coeff. (Cwp) 1,036
    LCB from zero pt. (+ve fwd) m 11,039
    LCF from zero pt. (+ve fwd) m 8,044
    KB m -5,648
    KG m 2,200
    BMt m 0,020
    BML m 11,910
    GMt m -7,829
    GML m 4,062
    KMt m -5,629
    KML m 6,262
     
  2. TANSL
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    TANSL Senior Member

    Have you checked if the baseline and fore and after perpendiculars are well placed?
     
  3. Ad Hoc
    Joined: Oct 2008
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    Ad Hoc Naval Architect

    None of your values make sense.

    1) WPA = 6.429m^2.
    The Lwl = 11.491, the Bmax = 0.542. So the maximum possible area is 11.491 x .542 = 6.228m^2. So your hull is basically box shaped?!

    2) Your Hull Coeff's, cannot be greater than 1.0.

    3) Your KMt is negative?!

    4) GM = KM - KG = -5.629 - 2.200 = -7.829m Yours 4.062?!

    And so on....none of your values make sense.
     
  4. NavalSArtichoke
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    NavalSArtichoke Senior Member

    KMT is negative becuz KB is way negative and BMT is tiny.

    LCB is approx. equal to LWL ?!?

    You have both block and prismatic coefficients >> 1 !!!

    If you haven't plotted this hull, you should do so immediately.
     
  5. sn1987
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    sn1987 Junior Member

    Thanks to all. Yes all the results haven't sense. But i don't know how it is possible. Could it be that the keel is not well trimmed and the software cannot establish the correct shape?anyway tomorrow I will upload the file with model.
     
  6. NavalSArtichoke
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    NavalSArtichoke Senior Member

    Who knows? You can't be sure unless you make a plot of the hull. There are too many things wrong with the output for it to be a simple mistake.
     
  7. sn1987
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    sn1987 Junior Member

    Hi,
    Herewith enclosed the maxsurf' file. let me know..thanks
     

    Attached Files:

  8. JSL
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    JSL Senior Member

    Interesting values - almost like you have inverted the coordinate system.
    any chance of posting this in a more common format (pdf, etc). so people who don't use maxsurf can offer you some help.
     
  9. TANSL
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    TANSL Senior Member

    Where is your zero point?. You should check the ship's coordinates system, "Base Line" and "Zero Point", in Maxsurf model
     
  10. NavalSArtichoke
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    NavalSArtichoke Senior Member

    Jeez, why is it so difficult just to plot your hull?

    A plot would probably answer all outstanding questions about what went wrong.
     
  11. JSL
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    JSL Senior Member

    Not I got it.
    LWL = 11.49
    LCB = 11.03
    LCF = 8.04
    Vessel is a container, taken on water and flooded in one end, sitting vertical (trim 90 deg)....... in the final stages of sinking.
    No need for maxsurf, could be done in 'etch-a-sketch'.
     
  12. sn1987
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    sn1987 Junior Member

    ok. I uploaded the body plan, profile and plane view of the boat in pdf. Anyway the base line is setted to 0 m (both vertical and longitudinal)
     

    Attached Files:

  13. TANSL
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    TANSL Senior Member

    The origin of coordinates seems fine though not know where the baseline.
    I can not open your file Maxsurf. Perhaps it corresponds to a higher version 14, which is what I have.
    For hydrostatics calculations and KN curves you do not need the superstructure. If you delete it you will get a much simpler model.
     
  14. sn1987
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    sn1987 Junior Member

    you could try with this version of file that should work with the older version of maxsurf. Anyway if you open file look the keel zone highlighted in the profile. maybe it isn't bonded correctly.
     

    Attached Files:


  15. Don92
    Joined: Feb 2015
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    Don92 Principal Naval Architect

    Hi sn1987, I took a look at the file you uploaded and the problem lies with the model you have made. Having looked at the frames Maxsurf has calculated, they appear a total mess. This is also clear from the curve of areas which doesn't look right at all. Judging from where the frames were distorted I would say your problem area is the keel. The best thing to do would be to ensure there are no gaps between surfaces here.
     
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