Damage stability of a ship is its capacity to resist damage situations caused by flooding due to the water overflows into bilges while ship stability is all about ship’s performance on still water and waves. Centre of gravity and centre of buoyancy of ship is the main factors taken into account in ship stability.
Damage stability and its after effects
Considering the stability of a ship during its damaged condition is very much necessary. The loss of stability is often seen due to the flooding caused by certain reasons. The water accumulation in hulls normally reduces the centre of gravity increasing the maetacentric height. What actually happens during the flood is that, water overflows into bilges making the ship erect and stationary. Loss of stability also occurs when an empty tank is holed and is filled with water causing to the loss of buoyancy of ship.
Damage Stability Calculation is probabilistic in nature
As far as calculation of damage stability is concerned, it is of probabilistic nature especially for merchant vessels. It deals with the probability of occurrence and that of survival i.e. the damages are combined with consequences producing a damage stability index number which abides by certain regulations. This probabilistic concept took its existence in 1973 and was adopted by relation A.265 (VIII) after a detailed study of data on collisions gathered by IMO.
The detailed study by IMO displayed a collection of accidents; the analysis of which it was found that the front part of the ships suffered the most during the accidents. Later the same was taken into account to improve the designs of ships and to avoid such accidents in future. The probabilistic concept based on the ship, its conditions, weather conditions, sea state, damages caused is preferred far beyond the deterministic method based on theories. Probabilistic approach brings about a set of regulations which includes a standard method of calculating the stability. This concept or approach was established in 1978 in SOLAS regulations for passenger ships while the same for cargo ships in 1990.