# Searching a VERY basic GZ curve creation software based on hydros and KN

Discussion in 'Stability' started by Pascal Warin, Jun 25, 2014.

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### Pascal WarinJunior Member

Hello everybody
From time to time (say.. every 10 months) a user of VeriSTAR Stability comes to request me how to perform simple GZ curve calculation based on interpolation of hydrostatic and cross-curves entered manually.
Can any of you suggest any such tool whether free or at low price (say <1000 US\$) ?

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### TANSLSenior Member

I think that program, as I understand what you say, does not exist but it would be very easy to do.
The most laborious is calculate hydrostatics, transverse stability curves, the position of the center of gravity, equilibrium waterplane. If you already have that, why do you need a program to do the easiest part of the whole process?.
So I think not to quite understand you. Could you, please, be more specific about what data you really want to start from?

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### athvasSenior Member

I think you can do it with Excel.

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### NavalSArtichokeSenior Member

If the KN curves have already been calculated, then you just need to read the values of KN for the range of angles at a constant displacement.

The formula: GZ = KN - KG sin (theta) can be calculated using a spreadsheet, for each angle theta. This is a trivial calculation.

Are you also interested in evaluating the area under the GZ curve as well, to see if the vessel satisfies some stability criteria? That is a more interesting proposition.

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### TeddyDiverGollywobbler

+1
Excel or OpenOffice..

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### Pascal WarinJunior Member

Thanks to all but I know that I can do it with Excel but if we want to be able to enter many KN and hydros on various trim and do the interpolation it will need development.
Also we had bad experience with Excel specially when changing version or language.

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### TANSLSenior Member

Pascal, looks like you have everything well controlled. Really, I do think this would have not required consultation, because, apparently, you already knew the answer.
Allow me a question, of many that are in the air, how do you calculate the equilibrium waterline in each load condition?. If you do not know this information, it is difficult to determine what KN curve should be used.
Excel, you're quite right, can create a problem if you do not know how to use it.

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### Pascal WarinJunior Member

Longit equilibrium is calculated as manually from the position of LCG and LCB with rotation around LCF.
Now excuse me but this is outside the scope of this topic.
I know how to do the job but I am looking a "from the shelf" solution.

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### TANSLSenior Member

If, as it seems, you know everything except the GZ, the formula given by NavalSArtichoke is correct, and then only, to calculate this parameter. A calculator is enough, unless you want to use a spreadsheet.

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### Pascal WarinJunior Member

My concern is NOT TO HAVE to prepare anything.

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### TANSLSenior Member

When you know what you need, tell me because I'm sure I can help. I can even make an application, just for you, to carry out that which you WANT NOT HAVE TO PREPARE.
Like I said earlier, you need to know what you want to do, what data you want to start from and what results you want to get. Think about it and we´ll talk.
Cheers

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### jarmo.hakkinenJunior Member

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### TANSLSenior Member

Our friend Pacal apparently works in the Bureau Veritas, Paris, and one must assume that he has access to the software of this company. VeriSTAR Stabilithy is a great program developed by BV and for that, I just do not understand what the problem is and how Pascal wants to solve it.

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### Pascal WarinJunior Member

I need just an interpolation program based on hydros and cross-curves tables entered by user. similar to what you do when calculating things manually on board from the T&S booklet data.

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### TANSLSenior Member

Do not give more turns to the problem. In post # 4 NavalSArtichoke said GZ = KN - KG sin (theta).
In booklets of stability, among other procedures for the KG, that is the formula that is proposed to the captain of the ship. As much as we try, there is no other formula and a simple handheld calculator, even with mobile phone, you can get the values.
Attached are some tables that are usually included in the stability booklet to assist the Captain in his calculations, as it might help you in something.
Like I said previously, if you indicate me the data starting from and where you want to go, I'm sure I can help more accurately.

#### Attached Files:

• ###### Tablas Cuadernillo.doc
File size:
244 KB
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