Large list time before capsizing

[naserrishehri]

Dear friends
I have seen some videos of cargo ships during capsizing. Most of them stay on large list(more than 5 deg.) For around 30 minutes then get capsized.
I guess in that list degree, the amount of GM is negative but not so much big to roll the ship by high speed. Do you agree?

 

[Lopolito]

Hi. When a ship's GM (metacentric height) is negative, it becomes unstable and prone to capsizing. I haven't watched the videos you mentioned, but if the ship is damaged, flooding may occur, and initially, the GM could still be positive. However, as flooding progresses, the GM gradually decreases until it becomes negative, at which point the ship capsizes. Additionally, you must consider the external forces, such as wind and waves, which can further impact stability.

But the point here is, when GM is negative, your vessel is going always to capsize.

 

[naserrishehri]

Hi. When a ship's GM (metacentric height) is negative, it becomes unstable and prone to capsizing. I haven't watched the videos you mentioned, but if the ship is damaged, flooding may occur, and initially, the GM could still be positive. However, as flooding progresses, the GM gradually decreases until it becomes negative, at which point the ship capsizes. Additionally, you must consider the external forces, such as wind and waves, which can further impact stability.

But the point here is, when GM is negative, your vessel is going always to capsize.

the ship capsized because of wrong loading containers in that case.
آپارات - سرویس اشتراک ویدیو https://www.aparat.com/v/r84ecvg

 

[TANSL]

@Lopolito, don't need to have a negative GM for boat to capsize.

 

[naserrishehri]

@Lopolito, don't need to have a negative GM for boat to capsize.

Thanks.
I belieave that there is a heel angle at which waterplan area is maximum and from zero heel up to that angle, heeling speed is fast and after that , heeling speed decrease but heeling continue up to capsizing.

 

[TANSL]

I believe that the speed in heeling does not depend on the GZ or DN curves but rather on the magnitude of the heeling moment, which is a variable totally independent of the hull shapes.

 

[Lopolito]

@Lopolito, don't need to have a negative GM for boat to capsize.

Didn't say that.

 

[naserrishehri]

I believe that the speed in heeling does not depend on the GZ or DN curves but rather on the magnitude of the heeling moment, which is a variable totally independent of the hull shapes.

So in this case, during loading containers KG increase and GM get zero then ship start to heel up to angle of loll (appx. 10 deg.) and stay 30 minutes in this angle then holds flooded and capsize.
below video is continue of previous :
آپارات - سرویس اشتراک ویدیو https://www.aparat.com/v/g75s3y2

 

[Lopolito]

the ship capsized because of wrong loading containers in that case.
آپارات - سرویس اشتراک ویدیو https://www.aparat.com/v/r84ecvg

In the video I see that the mooring is holding the ship, so it may have an influence on the speed of capsizing. In my opinion, there could be a bad cargo positioning inside the ship, leading to this, there was a simila problem in Valencia.

 

[TANSL]

Didn't say that.

Okay, so what did you mean by this statement? :

the GM gradually decreases until it becomes negative, at which point the ship capsizes

 

[Lopolito]

Okay, so what did you mean by this statement? :

This statement says that when GM is negative, in general terms, your vessel is likely to capsize. It does not state that having a negative GM is the only way a vessel can capsize.

 

[TANSL]

Could you show me a situation where the GM is negative? I don't doubt that such a situation exists but at the moment I can't think of what it could be. And in any case, what metacentre are you referring to because the position, both the real metacentre and the false metacentre, changes when the floatation changes.
In the second part of your last post it seems to be deduced that I have said something that I have not said.
Thank you for your time.

 

[Lopolito]

Could you show me a situation where the GM is negative? I don't doubt that such a situation exists but at the moment I can't think of what it could be. And in any case, what metacentre are you referring to because the position, both the real metacentre and the false metacentre, changes when the floatation changes.

Of course!. It depends a lot, in general terms it appears when your CDG gets too high. You can reach a negative GM for example if you don't ballast your vessel properly. Also, loding it excessively and on high decks (I have colleagues that have seen fishing vessels putting fish on the top of the bridge ). Another rare case could be ships with huge cranes.

Some ships have lolling, and the initial GM is negative, however this does not mean you’re going to capsize.

In those cases, the vessels tends to roll to one side and another.

It is evident that a negative GM is very strage, but fortunately, to see a ship sinkinkg is also very uncommon

In the second part of your last post it seems to be deduced that I have said something that I have not said.
Thank you for your time.

So sorry if there was a misunderstanding!

 

[naserrishehri]

Okay, so what did you mean by this statement? :

Do you agree with my statement?
The angle at which the ship staied for around 30 minutes (appx. 10deg.) Was angle of loll.
Am i right?

 

[TANSL]

@Lopolito, the curve you have drawn only shows us that the ship has a permanent initial inclination other than zero. It does not mean that it has a negative GM, since the tangent to the curve at the initial position is positive. When the initial inclination is zero, the tangent to the curve coincides with the initial GMt, which is not the case for your curve.
@naserrishehri, I'm sorry but I don't know what angle you are referring to.
The ship probably suffered a shift in cargo, which quickly caused it to list somewhat. From there, I suppose, water entered the holds, which created free surfaces in some of the holds and, in addition, greatly reduced the inertia of the float, with the consequent decrease in the height of the false metacentre. The speed of the list will depend, of course, on the speed of entry of the water.
Probably, if water had not entered and the holds and cargo had not moved further, the ship would have remained listed but in equilibrium in said list.