# Maxsurf stability problem

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

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### sn1987Junior 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
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

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### TANSLSenior Member

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### Ad HocNaval 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.

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### NavalSArtichokeSenior 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.

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### sn1987Junior 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.

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### NavalSArtichokeSenior 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.

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### sn1987Junior Member

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

#### Attached Files:

• ###### stability.msd
File size:
78.6 KB
Views:
579
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### JSLSenior 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.

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### TANSLSenior Member

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

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### NavalSArtichokeSenior Member

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

A plot would probably answer all outstanding questions about what went wrong.

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### JSLSenior 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'.

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### sn1987Junior 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:

File size:
56.4 KB
Views:
399
File size:
40.1 KB
Views:
361
• ###### profile.pdf
File size:
42.1 KB
Views:
346
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### TANSLSenior 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.

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### sn1987Junior 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:

File size:
46.2 KB
Views:
329
• ###### Untitled.msd
File size:
18.4 KB
Views:
484

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### Don92Principal 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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