# Stability prediction

Discussion in 'Stability' started by Alexanov, Sep 20, 2017.

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### AlexanovSenior Member

It is may be stupid question from my side- can we say something about ship's stability if we will have a possibility to meassure dinamically heel, trim, hull motion and axeleration? Does anyone have shuch experience? It's may be similar to heeling test?

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### gonzoSenior Member

You could do that. However, it will be very difficult to evaluate the input. That is why inclination and other tests are run in controlled conditions

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### TANSLSenior Member

Interesting, yes, very interesting. What would be the procedure ?. What would be more difficult to evaluate the input or evaluate the output? By the way, what would be the input?

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### gonzoSenior Member

The procedure is to gather data, usually through sensors, and then analyzing it. This method is used extensively in field tests. For example, accelerometers are installed to measure slamming loads. In this case the input would be waves vs speed.

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### TANSLSenior Member

Of course, now I understand. The procedure is data collection, not what data are collected or/and how they are collected .
By the way the accelerometer can not collect loads, it can only measure accelerations. Or am I wrong once more?
What exactly, number of waves, height and frequency of waves, energy of waves, .... speed of boat, speed of waves, speed of boat relative to waves or respect to the coast?.
Thank you, as always, for your explanations.

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### AlexanovSenior Member

I think it is possible to filtrate regular accelerations from speed and waves. Ship's motion related to stability is not so regular I think.

Last edited: Sep 21, 2017
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### gonzoSenior Member

It is a complex analysis. For example, the accelerometer data can be used to calculate force. The problem is that if you don't know what the external forces are, you can't use that data to calculate stability. Usually those dynamic measurements are used to verify the predicted behavior of the vessel or any other system. For example, the design calculations predict that the vessel won't roll more than 6 degrees in waves of 5 meters height and winds of 40 knots. The data will either verify or not that prediction. Otherwise, you could introduce a disturbance (force) that is calibrated and then measure the reaction.

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### AlexanovSenior Member

it is interesting to see how real measurments looks on diagrams. what can it be? May be heel, trim, linear acceleration vector, rotation vector? interesting to study how it is looks in defferent stability cases. Probably this inforation possible to find in model tanks. Will try to contact ship model tank in Trondheim.

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### gonzoSenior Member

Model test tanks control the conditions, so they can analyze the responses. You can vary one or more at a time.

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