Submarine Hull - Pressure Hull

Pressure Hull

Inside the outer hull there is a strong hull, or pressure hull, which actually withstands the outside pressure and has normal atmospheric pressure inside. The pressure hull is generally constructed of thick high-strength steel with a complex structure and high strength reserve, and is separated with watertight bulkheads into several compartments. The pressure and light hulls aren't separated, and form a three-dimensional structure with increased strength. The interhull space is used for some of the equipment which doesn't require constant pressure to operate. The list significantly differs between submarines, and generally includes different water/air tanks. In case of a single-hull submarine, the light hull and the pressure hull are the same except for the bow and stern.

The task of building a pressure hull is very difficult. No matter how large the submarine is, its hull must be constructed with high precision. Inevitable minor deviations are resisted by the stiffener rings, but even a one inch (25 mm) deviation from roundness results in over 30 percent decrease of hydrostatic load. The total pressure force of several million tons must be distributed evenly over the hull and be oriented longitudinally, as no material could resist such force by bending. A submarine hull has to use expensive transversal construction, with the stiffeners rings located more frequently than the longitudinals. All hull parts must be welded without defects, and all joints are checked several times with different methods.