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.
