# How to find GG1 without the lenght of vessel

Discussion in 'Boat Design' started by Adeyele, Oct 7, 2012.

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A vessel with a displacement of 100000 tonne has two tanks, one 'x' metres aft of the ship centre of gravity, the other 'y' metres forward of the ships centre of gravity.

When 120 tonne of fuel is moved from the aft tank to the forward tank, the centre of gravity moves 0.9m forward. 500 tonne of fuel are now consumed from the forward tank causing the ship centre of gravity to move 0.5m aft of the original centre of gravity.

Calculate the distance 'x' and 'y'.

Any help is welcomed.

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### gonzoSenior Member

It depends on the shape of the hull. If it was a regular shape, that is a prism with square or rectangular section, it would be possible to calculate that somewhat easier. However, it would also depend on the shape of the tanks.

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This has nothing to do with shape of hull or shape of tanks. Nonsense, it is just a simple moment calculation. The moments of moving the weights must balance and thus be equal.

For the first movement:

The GG = (distance)/ weight

so

0.9 = (x + y)/100,000

The second is

0.5 = 500y/99,500

So, you can now calculate y, and then using that value insert into the first equation.

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### gonzoSenior Member

Irregular shaped tanks have their center of gravity change in a direction other than vertical. Also, the attitude of the hull changes the position of the center of gravity. Where is the nonsense in that?

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Read the question from the OP. What data is given and what data is required.
It is simple for any NA, but not a student learning. Shape of hulls/tanks etc bears no relevance to the question.

It is just moments, nothing else.

If you wish to read more into it, that's your prerogative, but it does not alter the result nor the method or calculation. It is an unfortunate misdirection which shall only confuse the OP.

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### gonzoSenior Member

It is the typical word question that doesn't have all the relevant information. I know it is possible to learn how to answer them to pass a test, but it is a method that leads to failures in real life.

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tnks to all for all the reply. The question has nothing to do with the shape of the tank, its just abt changes in the centre of gravity of a vessel due to shifting weight. tnks to Ad Hoc for some little advice, but in the first one, u didn't include the weight 120tonnes? can u explain this ommision?

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