naval architecture, the science of designing ships, submarines, floating docks, yachts, oil rigs for the offshore oil and gas industry, and any craft for use on water. Those qualified to work in this area are known as naval architects.

Until the late 16th century, when plans for constructing new ships began to be drawn on paper, the shipwright's trade was a closely guarded mystique. The necessary expertise was handed down by word of mouth from father to son, as ships were built solely ‘by eye’ using traditional ‘rule-of-thumb’ methods. As a result, improvements in ship construction were introduced only slowly against deep-rooted suspicion and dogmatism.

The work of early naval architects was unscientific and generally followed specifications of shape and scantlings which had been in use for generations. A more scientific approach was attempted by the Swedish naval architect Frederik af Chapman (1721–1808) and others. Chapman wrote a well-regarded treatise on the subject. But it was not until the British engineer William Froude (1810–79) began to study hydrodynamics and ship behaviour in the late 1860s, by undertaking more sophisticated tank testing, that any advance of importance occurred.

Modern naval architecture by Fred M. Walker

Nowadays, naval architects must handle a wide variety of tasks including economic viability studies, conceptual design, strength and stability calculations, as well as supplying the final working drawings for a ship. They may be asked to superintend ships under construction, to make the calculations for launching, and oversee the tests and trials required by a new vessel. The naval architect is also responsible for ensuring that the new ship meets Classification Society regulations as well as the Statutes of International Law as defined by the International Maritime Organization and other authorities. With the increase in complex technology there is now a much greater overlap with marine engineering, to the extent that most universities now offer combined degrees in Naval Architecture and Marine Engineering.

To design a ship, a series of calculations must take place, each defining one aspect of the ship, and in turn absorbing the results of previous calculations. The process has to be repeated several times—a process known as iteration—until the optimum ship design has been achieved. This is known as the design spiral (see illustration overleaf), and owing to the intense ‘number crunching’ required, is aided greatly by computers.

Basic Design.

This incorporates the main dimensions of a ship, with estimates of displacement tonnage and cargo-carrying capacity. In this part of the investigation, matters like depth of water in anticipated ports, air draft (maximum height allowable under bridges on the ship's anticipated route) and the owners' requirements for earning ability have to be incorporated into the calculations, and then a preliminary arrangement plan is drawn. The larger a ship, the more efficient is its capacity. For example, by doubling the dimensions of a ship, the cargo capacity increases eightfold, while the fuel consumption is unlikely to be more than double.

Amongst the plans of a ship, which may amount to hundreds, one should find: General arrangement (the internal layout) Lines plan (showing the complex contouring of the hull) Midship section (showing the structural strength at midsection) Structural profile (showing bulkheads and strength members) Rigging plan (giving external fittings and profile) Machinery arrangement Propellers (including bow and stern thrusters, propulsion pods) Stabilizers Electrical layout Cargo capacity or passenger plan Paint linesAs a matter of principle, all plans are drawn with the ship ‘steaming’ to the right-hand side of the paper, so that a rigging plan shows its starboard side. This international convention is vital, as information on the ship may be sent anywhere in the world, and all shipyards and ship repair establishments accept these conventions.

In the past few years the widespread introduction of computers has led to simplified ship plans, with in many cases the final drawings (where needed) being printed on paper as small as A3 size.

Selection of Machinery.

To ensure decisions are made correctly, the naval architect must know the routes the ship will work, its range of operation, and the availability of fuel. The vast bulk of modern ships have two-stroke or medium-speed diesel engines, and in these cases the weight, power, fuel consumption, and other matters can be predicted with great accuracy.

The availability of machinery spares must not be overlooked, although with modern air communications this seldom poses a problem. The options are immense, and the choice of machinery is endless.

In the final analysis an efficient design is one that uses material and local skills to produce a ship that is optimum for the trade envisaged. For example, the modern cruise liner has a need for maximum passenger capacity and quick turnaround in port. The current answer is a ship with underslung or podded propulsors energized by electric propulsion. The beauty of this configuration is that the alternators can be placed anywhere on the ship, whilst the main machinery is either within the propulsor or situated just above it, taking up little of the ship's vital earning capacity.

Once the ship has overall dimensions, machinery, and fuel capacity settled, the naval architect can compute capacity for passengers, crew, and cargo. Now the dimensions can be finalized and the final stages of the design spiral completed.

Tank Testing.

To ensure that the ship has an efficient and sea-kindly hull form, an accurate scale model, usually about 3 metres (10 ft) long, is built and taken through a series of controlled experiments from which the ship's performance can be predicted with accuracy. This form of ship model experimentation has been carried out for nearly 130 years, following the 19th-century pioneering work of William Froude. Tank simulations allow for model testing of rudders, thrusters, and, for passenger ships, the ubiquitous stabilizer fins. Ships carrying passengers may have wind tunnel tests carried out on their funnels and superstructures to ensure all soot and noxious exhaust fumes are blown clear of the decks.

With most decisions settled, the structure of the ship is designed to ensure the ship is strong enough for a long and arduous life. The key drawing is the Midship section which gives many technical particulars and the scantlings of all steelwork parts at a point of significant stress. From this the weights and centres of gravity of the ship in various conditions including unladen, ballasted, fully laden, and so on can be analysed and stability checked out. Now the design spiral is complete, although it must be rechecked for every small change in the basic design before the final plans are drawn up and sent to the shipbuilding yard responsible for the ship's construction.

For naval architecture terms not cross-referenced or mentioned in this entry see afterbody; block coefficient; body plan; buttock lines; centre of effort; centre of lateral resistance; heeling moment; prismatic coefficient; sections; simpson's rules; wetted surface.

See also yachtbuilding.

naval architecture science of designing ships. A naval architect must consider especially the following factors: floatability, i.e., the ability of the ship to remain afloat while meeting the requirements of the vessel's service under normal and abnormal weather and water conditions or after being damaged by collision or grounding; strength sufficient to withstand loads for which the vessel is intended; stability, i.e., the capability of the vessel to return to an upright position after being inclined by wind, sea, or conditions of loading; speed, which is affected by the outline of the hull and the type of engines, boilers, and propellers; steering, i.e., the design of the rudder and the hull structure to effect efficient turning; living conditions, including adequate ventilation and other health and safety considerations; and the arrangement of the structure and equipment to facilitate handling of cargoes. Additional problems are faced in the design of warships. Heavy, concentrated loads in the form of gun turrets, the protective armor, and other factors make warship design a field in itself. The three principal plans made for the construction of a ship are the sheer plan, a profile of the ship, showing the outline of the intersection of a series of vertical longitudinal planes with the shell of the ship and including the location of the transverse bulkheads, decks, and main structures; the body plan, a view showing sections made by vertical transverse planes; and the half-breadth plan, indicating the outline of a series of horizontal longitudinal planes. In addition, innumerable general and detail drawings are made, which include all the internal and external equipment.

Bibliography: See J. P. Comstock, ed., Principles of Naval Architecture (1967); R. Munro-Smith, Applied Naval Architecture (1967); T. C. Gillmer, Modern Ship Design (1970); B. Baxter, Naval Architecture: Examples and Theory (1977).

naval architecture the designing of ships.