A process which translates a set of owner's requirements into the drawings, specifications, and other technical data necessary to actually build a ship. Naval architects lead the process, but engineers and designers with many other skills contribute. These other skills include marine engineering, structural design, and production engineering. The ship design process is iterative, and is subdivided into several phases during which the design is developed in increasing degrees of detail. Typically, the owner's requirements specify the mission that the new ship must perform and define such parameters as required speed, fuel endurance, and cargo weight and capacity. Generally, the cost to build and operate a ship is constrained by the prospective owner. The ship design process involves numerous trade-off studies in order to achieve the desired capability and, at the same time, stay within the established cost. See also Naval architecture.
Mission requirements and constraints are unique to each ship being considered. For some ships, such as point-to-point cargo ships, the mission requirements can be simply stated; for example, “Transport 5000 20 ft ISO standard cargo containers at an average sea speed of 18 knots with 10,000 nautical miles between refuelings. On- and off-load the 5000 containers using shore-based cranes in less than XX hours.” For other ship types, such as industrial ships performing missions at sea, the mission requirements are more complex. The requirements for a fisheries research vessel, for example, might specify the ability to catch fish using several different techniques, radiated noise limitations, required sonar performance, and several different aspects of maneuvering and seakeeping performance, such as low-speed stationkeeping and the ability to maintain a specified track over the sea floor in the face of cross currents, winds, and seas. See also Merchant ship; Oceanographic vessels; Ship powering, maneuvering, and seakeeping.
Cost, both to design and build the ship and to operate it, is usually constrained. The two primary elements of operating cost are crew and fuel, so there is nearly always pressure on the designer to reduce crew size and fuel consumption. Physical constraints may also be imposed on the design related to construction, operational, or maintenance requirements. Weight or dimensional constraints may be imposed if the ship is to be built or maintained in a specific dry dock. Pier or harbor limitations may also impose dimensional constraints. Ship length may be limited by the requirement to tie up to a certain pier. Ship air draft (vertical distance from the water surface to the highest point on the ship) may be limited by the need to pass under bridges of a certain height. Ship navigational draft (vertical distance from the water surface to the lowest point on the ship) may be limited by the depth of a dredged channel in a particular harbor.
In addition to unique mission requirements and constraints, every ship must satisfy certain physical principles. The fundamental principles are that (1) the ship hull and superstructure must have adequate storage space, and (2) the ship must float at an acceptable waterline (draft neither too great nor too small) when it is fully loaded. Another principle is that the ship must be statically stable; that is, when it is displaced from its equilibrium condition, it must tend to return to that condition. For example, when the ship is heeled to one side by a disturbing force such as a wind gust, it must tend to return to the vertical rather than continuing to roll and capsizing. The ship's hull must have sufficient strength to withstand the forces that will act upon it over a range of loading and sea conditions. The ship must possess sufficient propulsive power to achieve the desired speed even with a fouled bottom and in adverse sea conditions. In addition, it must generate sufficient electric power to satisfy the requirements of mission systems; ship machinery; heating, ventilation, and air conditioning (HVAC) systems; hotel; and other ship services. See also Buoyancy; Hydrostatics; Marine engineering; Marine machinery.
