The measure of the ability of a ship to survive flooding accidents caused by collision or grounding.
- Attained Subdivision Index “A” – The probability of survival of a vessel after collision or grounding. “A” is taken as the sum of the products of probability p x s x v for each compartment or group of compartments where ‘p’ accounts for the damage position along the ship length, ‘s’ the probability of not capsizing or sinking after such fl ooding, and ‘v’ the assumed vertical extent of damage.
Recognising that the actual loading condition at the time of any damage may vary, the calculations are to be carried out for the ship loaded to the deepest subdivision load line and also at a partial loadline. The contribution to the total Attained Subdivision Index “A” for the calculations at each of these draughts is 0.5A at the deepest load line plus 0.5A at the partial load line.
- Required Subdivision Index “R” – A required probability of survival in flooded condition. For general cargo ships and container ships the required subdivision index depends on the ship length, for passenger vessels it depends on the ship length and the number of persons onboard.