Damage Stability(Lost Buoyancy)

Discussion in 'Stability' started by 91SARATH, Jul 13, 2016.

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91SARATHJunior Member

As per the Lost Buoyancy concept,which ever tanks get damaged, it will be subtracted from the hull and it will give rise to new Hydrostatics.

And new drafts will be found out resulting from the new displacement[Old Displacement - Outflow (if any)], new LCB,LCF etc.

Here where is the role of water ingress into those damaged tanks,how does it effect the calculation ??when all of these tanks are entirely subtracted from the hull to form a new Hydros.

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HeimfriedSenior Member

Hi, 91SARATH,
you speak about a "damaged tank". Does this mean the same as a "compartment" or "watertight subdivision" of the ships hull?

Means "damaged" open to the sea?

What is "it" you do subtract: the displaced volume of the tank?

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91SARATHJunior Member

Yes by tank, I meant water tight compartment.By 'Subtracting it' I meant what ever Compartment is damaged it will be excluded from the actual intact hull,to obtain a new Hydros & Kn.

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HeimfriedSenior Member

In the Lost Buoyancy concept this water is not a part of calculation. The effect of water inside an "open to sea" compartment is physically the same as the water outside the hull.

If the compartment is a tank filled with liquid the weight of the liquid is after damage no longer a part of the displacement mass (force). No matter if there is an outflow or not.

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RabahSenior Member

Hi 91SARATH,
The method of the lost buoyancy has also other name: "Constant displacement method". That is when you write about difference in displacement, you make a mistake. It will be better if you have well studied the Theory of unsinkability of the ships. It is very important to understand physical sense of the phenomenon:
The Displacement of the ship remains unchanged, there being a change only in shape of the immersed portion.
Coordinates of the ship's centre of gravity are not changed.
The draft, the trim, the heel /if deluging is asymmetric/, the coordinates of the centre of buoyancy and the coordinates of the centroid of square of the damaged water-line are changed.
When all this becomes understandable to you then and it is possible to start calculations on unsinkability on the constant displacement method as all Classification organizations require.
_____________________
NA Razmik Baharyan

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91SARATHJunior Member

Hi Razmik Baharyan,

Yes I agree there will be no change in Displacement in Lost Buoyancy method, but it is just one of the conventions(I hope,it is not widely observed too).

In most cases I have seen the total content of so called damaged compartments will be considered out flown if they are filled in Intact condition( especially Oil tanks or other liquid contents).But solid content and hull weight remain same.

Thus final displacement will be Intact displacement - Outflow.

7. Joined: Mar 2014
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Location: Bulgaria

RabahSenior Member

Hi 91SARATH,
The method of constant displacement is unique which Classification organizations suppose for calculation damage stability.
If you want to help you, I ask to straighten out and precisely to formulate with precise engineering terms substance of your problem.
From till now written by you it is not clear what you want also what help for you is necessary.
_________________________
NA Razmik Baharyan

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