An engineering discipline concerned with the design of ships, boats, drill rigs, submarines, and other floating or submerged craft. The naval architect creates the initial overall concept for a new ship, integrates the work of other specialists as the ship design is developed, and is specifically responsible for the hull and superstructure shape, general arrangements, structural design, weights and centers calculations, stability analysis, hydrodynamic performance assessments, propeller and rudder design, and the arrangement and outfit of all living and working spaces, other than machinery spaces. The naval architect's ally, the marine engineer, is responsible for the design of the propulsion plant, the electric plant, and other ship machinery and mechanical systems, including the so-called distributive systems: electric cabling, piping, and ventilation system ducting. The marine engineer also is responsible for ship control systems, including propulsion and electric plant controls and the steering system.