# Calculating kn values with maxsurf and AutoCAD

Discussion in 'Software' started by Siddarth Amaravathi, Apr 14, 2021.

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1. Joined: Apr 2021
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### Siddarth AmaravathiJunior Member

Gz = kn-kg*sin theta
Where,
Gz= gm sin theta
Gm= km-kg
Km= kb + bm.
Kb is center of buoyancy
Is this what you're asking sir?

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### TANSLSenior Member

No, is not that.
Those formulas are of little use to calculate the KN, if you don't know the position of the CoG and metacenter.
The value of the KN depends exclusively on the shapes of the ship and has nothing to do with the CoG nor with metacenter.
Could you make a drawing, and show it here, with the position of the CoB and what is the KN?

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### Siddarth AmaravathiJunior Member

sir since its a rectangular one, I've considered cob at the center of the area underwater and I heeled the vessel to 10 degrees about the cog which is center of the whole vessel. hope this satisfies the question you asked

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### TANSLSenior Member

Before trying to calculate the KN you should find out what that is.
Forget CoF and CoG and center yourself in CoB and what we know as KN.

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• ###### KN-2.jpg
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### Siddarth AmaravathiJunior Member

woah. I'm perplexed right now. Could you explain me stuff please

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### TANSLSenior Member

Frankly, I don't know what else you need me to explain. Should I clarify that instead of an inclination of 10º, in my picture of post # 19, I have considered an inclination of 30º to make it more evident, clearer, what each point is.
Once the position of the center of buoyancy is known (and AutoCAD will give it with complete accuracy), trigonometry will allow you to obtain the value of the KN. If this is not enough, please look at the formula in the picture to the right of post #19.

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### Siddarth AmaravathiJunior Member

I was actually wondering, about what point did you heel the ship to 30°. how are you titling it. Please explain stepwise what did you do in cad. I'm really sorry I'm asking you too many questions but then you're a gem teacher I could get.

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### TANSLSenior Member

Do you know how to create a solid model of your barge in AutoCAD?

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### Siddarth AmaravathiJunior Member

Yes

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### TANSLSenior Member

You must cut the solid through successive 10-degree inclined planes until you get a sectioned piece with a volume of 976 m3 (equivalent to 1000 tons). Get closer little by little until you get more or less that volume. Once achieved, the AutoCAD command "_massprop" will provide all the properties of the solid, including the position of the center of gravity of its volume, which is the center of buoyancy sought. With that data you can now use the previous formulas to calculate the value of the KN.

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### Siddarth AmaravathiJunior Member

ok now I get it

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