Unsinkability

of a vessel, the ability of a vessel to remain afloat and not capsize when its hull is damaged and one or more compartments are flooded; the most important element in the survivability of a vessel.

In practice, the unsinkability of a vessel is its ability to meet the standards for buoyancy and stability set forth by a classification society for the given type of damage. The most rigorous requirements apply with regard to the unsinkability of passenger vessels. The unsinkability of a vessel is enhanced by the internal division of the hull into watertight compartments both vertically (by decks) and horizontally (by partitions); other measures include connecting compartments located on opposite sides of the ship and constructing a double bottom. A damaged vessel can be kept afloat if vessel list and trim are prevented by flooding compartments that are symmetric to the damaged compartments and if stability is restored by the intake of ballast in the lower compartments.

The concept of unsinkability was first introduced by the Russian scientist and naval commander Admiral S. O. Makarov. The theory of unsinkability was formulated by Academician A. N. Krylov and supplemented and developed by I. G. Bubnov, R. A. Matrosov, and V. G. Vlasov, among others.