It is important that a ship should be capable of sustaining at least a moderate degree of damage without sinking or capsizing. Ships are usually subdivided internally into watertight compartments to limit the extent of flooding that follows structural damage due to collision, grounding or stress of weather. During the design of the ship calculations are carried out to enable the naval architect to define a satisfactory disposition of major bulkheads to meet suitable safety standards and to examine the consequences of flooding certain spaces, or combinations of spaces, within a ship. With certain classes of ship, principally those carrying passengers, there are legal requirements to meet certain standards of subdivision. For other ships there is no legal necessity to meet such requirements, but the ships are allowed to load to a deeper draught if they do. Naval vessels must obviously meet very high standards of subdivision in order to fulfil their military role. Leisure craft are a special case in that foam-filled buoyancy spaces are frequently used to ensure the craft survives damage. Nevertheless calculations are still needed to obtain an adequate disposition of such buoyancy.