Damage Stability

Can anyone explain what it means by "tank runoff in damage stability analysis"?

 

It may refer to the loss of liquid that occurs in a tank due to the gap caused by the damage.

 

Ok. So, when i damage a fuel oil tank, then it means the tank now contains a mix of FO and SW? Which density should be take into consideration? Or Maxsurf will all do it for you?

 

I do not know how Maxsurf calculates, although in its manuals it usually explains the theoretical part on which it bases its calculations.
When calculating stability after damage by the deterministic method you can use 2 methods for the analysis:

1. Buoyancy Loss Method (or Submerged Volume)
2. Method of Weight Increase by Flood.

The latter has the advantage of considering the same shape of the submerged hull of the vessel, so that the Hydrostatic and Crossr Curves are applicable (which does not happen with the Thrust Loss Method).
If a flood has occurred and the water completely fills the compartment, for example a double bottom tank, the situation is the same as it would have been routinely filled, so it will even improve the stability by adding a 'low' weight, although consider the loss of 'buoyancy reserve'.

If the flood does not completely fill the compartment, the following phenomena will occur:

a) Weight gain due to water entry, which will cause rise or fall of G, depending on the location of the flooded liquid.
b) Ascent of G due to "free surface"
c) Variation of the position of M, due to the increase in draft (and displacement).
d) If there is Free Communication with the Sea, the additional effect of "loss of stability through Free Communication with the Sea" should be considered, which will be seen later.​

The effect is that when the ship heels towards the damage band 'water' enters which will heel the ship even more. When the heeling to the opposing band, water will flow out of the flooded compartment, which will heel more the ship. That is to say, in both bands the list will increase, which implies that the ship has 'lost' stability.

 

No...it is assumed the more dense fluid will replace the less dense fluid.

However you need to be sure how the tank is arranged and how it influences the stability...and if any progressive flooding of the tank and/or void is possible from said damage.