Ship is the general term for any type of large buoyant vessel in which people travel or transport goods over the surface of the water. The term boat usually denotes smaller vessels, but no criterion of differentiation is generally accepted. The term shipbuilding is applied to the construction of large vessels. See also BOATS AND BOATBUILDING..

EARLY TYPES OF VESSELS

Early societies used rafts, skin- or bark-covered canoes, and dugout canoes for water travel. In the most advanced type of early vessel a wooden framework of ribs and longitudinal pieces was covered with a skin of thin wooden planks. Modern types of ships used in Europe have developed for the most part from the early boats used by the Egyptians and other Mediterranean peoples.

Egyptian Vessels.

The earliest known Egyptian ships employed a wood framework covered with wood planking and were large enough to accommodate at least 20 oarsmen and to carry a cargo of several head of cattle or an equivalent weight of goods. The first pictorial records of these galleys date from as early as 3000 bc, and ships of this type were probably in use for some time before that date. Ships illustrated in early Egyptian paintings were equipped with a double mast, joined at the top, from which sails were hung. In later types, a single mast was used and the sails were hoisted by means of rollers at the top of the mast. Steering, in all the early Egyptian vessels, was accomplished by means of one or more steering oars or sweeps that projected over the stern of the vessel. When more than one oar was used in steering, the steering oars were attached to each other and were directed by means of a single steering arm or tiller.

Phoenician Vessels.

The most able shipbuilders of ancient times were the Phoenicians (2000 bc), who constructed not only merchant vessels capable of carrying large cargoes, but also warships larger and more effective than any built by their contemporaries, the Egyptians and the Aegeans. The Phoenicians' most significant contribution was the “round boat”—a broad-beamed ship that depended principally on sails rather than oars and provided a much larger cargo space than the narrow galleys. Phoenician round ships traveled the Mediterranean and beyond: to Britain (for trade in tin), and probably far south along the African coast.

Phoenician shipbuilders are also credited with developing bireme and trireme galleys in which the oars were arranged in two or three banks. Multibanked galleys are a matter of scholarly dispute. Some authorities, who doubt that the quinquiremes of the Greeks and Romans actually had five banks of oars, suggest that the term means merely that five rowers were assigned to an oar.

Greek Ships.

Although no evidence remains, the framework of the Greek galleys supposedly was made of naturally curved timber, or crooks, in a manner similar to that used in present-day shipbuilding. A superstructure was built at the after end of the deck to house and protect the captain and officers, and at the forward end of the ship the deck was also raised to form a structure called a forecastle. Other features of the Greek galley included a series of rope girdles that were strung around the sides of the ship in a fore-and-aft direction and arranged so that they could be tightened by levers at the rear of the vessel. These girdles served a double purpose: They strengthened the ship against the shock attendant upon ramming another ship in battle and also functioned as a longitudinal truss. The galleys were also equipped with one or two masts for sailing, but sails were not used when a galley was engaged in battle. The crew of a Greek warship was made up of approximately 220 men, most of whom were oarsmen.

Roman Ships.

The Romans developed many different kinds of warships over their long period of Mediterranean dominance, notably galleys that employed bridges for boarding enemy ships and some that carried catapult artillery. For commerce the Romans built ships of up to 53.4 m (up to 175 ft) in length and about 14 m (about 45 ft) in breadth and depth. Even larger ships are believed to have been built for transporting obelisks from Egypt to Rome. These large cargo ships were rigged with square sails on three masts and may have carried a topsail above the mainsail on the mainmast.

The final development of the Roman warship was the dromond, a swift galley with one or two banks of oars, which was used in the 5th century ad. During this period and later, warships were improved by the addition of various forms of protective coverings, such as leather and vinegar-soaked cloth, to guard against the incendiary and explosive missiles that had become a part of naval armament.

Norse Ships.

Concurrent with the improved Roman galleys were the highly efficient long ships, which were oceangoing vessels propelled by both oars and sails, developed by the Vikings and Danes in Scandinavia. The smallest class of these ships, called snekkja, had about 30 oars, and larger classes had 64 or even more. The remains of a snekkja, found in a burial mound in Norway during the latter part of the 19th century, was 23.8 m (78 ft) in length, 5 m (16.5 ft) in width, and slightly under 1.8 m (under 6 ft) in depth. The round ship, or skuta, which was primarily a sailing vessel that could also be rowed, was used in Viking expeditions to Greenland and Iceland, and also by the various Scandinavian kings who invaded the British Isles. This type was adapted by the Saxons, notably under Alfred the Great, for defense against raiders.

The Chinese Junk.

At about the same time the Chinese developed one of the strongest and most seaworthy vessels in existence: the junk, which is still used by the peoples of Southeast Asia. Essentially a large, light flat-bottomed box, the junk lacks three components elsewhere regarded as fundamental to ships: keel, and stem- sternposts (upright members at bow and stern). Its hull is partitioned off by solid bulkheads running lengthwise and crosswise to divide it into watertight compartments. Such bulkheads, which were not adopted by the West until the 19th century, not only make the ship structurally rigid, but also protect it against sinking. The lack of a keel is compensated for by a heavy steering oar or rudder, mounted on the centerline through a watertight housing in the bottom. The rudder can be raised or lowered. The sails are made up of narrow horizontal linen or matting panels, each secured by its own line or sheet, so that each sail can be quickly spread or closed.

By the 9th century ad, Chinese junks were carrying merchants to Indonesia and India. In his Travels, written in 1298, the Italian traveler Marco Polo praised the bulkhead system that kept the vessel from sinking “if she springs a leak by running against a rock, or on being hit by a hungry whale.” By the 15th century junks were sailing to East Africa.

LATER VESSELS

The ships of medieval Europe were, in general, developments of the Roman galleys, but they used much longer oars, or sweeps. These oars frequently were as long as 15 m (50 ft) and were powered by as many as seven rowers at each oar. The inboard portions of the oars were counterbalanced and equipped with handles; the rowers were arranged in tiers on ramps. To provide greater leverage for the long oars, the tholes, or pins, against which the oars were pulled, were mounted outside the hull of the ship on a wooden framework, called an apostis, running parallel to the centerline of the ship. First used on ancient galleys and reintroduced on medieval ships, the apostis had the same purpose as the outriggers used on modern racing shells. Use of the apostis also facilitated the arranging of the oars in two or more banks on each side of the vessel.

Other improvements introduced in the Middle Ages included the use of a permanent rudder hung from the sternpost of the ship in place of the steering oars used by the Romans. In addition, the ships of later medieval times were made with a greater freeboard (higher sides above the waterline) to make them more suitable for use in rough or stormy seas.

The typical warship of the Middle Ages was the medieval galley, which was brought to perfection by shipbuilders of the Mediterranean area, particularly by the builders of Genoa and Venice. Galleys varied in length from 30 to 60 m (100 to 200 ft) and were commonly propelled by 20 oars on each side together with sails rigged on two or three masts. Beginning with the 15th century, galleys were armed with cannon on the forecastle deck and on the high poop deck at the stern. In later models of the galleys, guns were also mounted to fire broadside over the bulwarks of the ship and, still later, to fire through openings or ports in the bulwarks. The larger galleys carried as many as 1200 men.

Until the end of the Middle Ages no clear distinction was made between naval and merchant sailing ships; vessels with sails were used both as warships and as merchantships, although oared ships were restricted largely to military purposes. At about the beginning of the 15th century, however, various nations began to develop distinctive types of vessels for fighting and trade. A typical merchant ship of the late Middle Ages was the carrack, a strongly built, three-masted vessel, carrying two courses of square sails on the foremast and mainmast and a lateen sail (a triangular sail attached to both a mast and a yard) on the short mizzenmast. Such ships were equipped with only a limited amount of armament and were designed primarily for carrying cargo.

Sailing Ships.

Near the end of the Middle Ages the use of oars for propulsion began to give way to the exclusive employment of sails, particularly in vessels built in northern Europe for use in the Atlantic Ocean. The Mediterranean nations, particularly Italy, continued to build galleys, and as late as 1571 the Christian fleet that fought the Turks at the Battle of Lepanto was composed almost exclusively of galleys. Subsequently, various classes of rowing-and-sailing warships, such as the galleon, were developed by the Mediterranean nations; these types replaced the galley ships by the late 1700s.

Early European types.

European nations developed many types of sailing ships. The caravel, typical of Portugal and Spain, was a comparatively small vessel, usually of about 113 metric tons burden (cargo capacity), but sometimes larger or smaller. The caravel had a broad bow and a high, narrow poop deck. It was rigged with three or four masts, of which only the foremast carried a square sail, while the others carried lateen sails. The ships in which Christopher Columbus sailed on his voyages of discovery were caravels.

The typical European warship of the 16th and 17th centuries was the so-called great ship, with four or five masts, high forecastle and poop decks, and two or more tiers of guns. These ships reached displacements of 900 metric tons or more and carried at least 60 guns. Later, armaments were increased, particularly in the British navy, so that ships of 100 guns were not uncommon. The flagship of the British admiral Horatio Nelson, the HMS Victory, built in the middle of the 18th century, typified the large man-of-war style of the period. The Victory was 56.7 m (186 ft) in length, 15.9 m (52 ft) in beam or width, and had a displacement of 2197 metric tons. Lighter types of warship were the frigate and sloop, or corvette, full-rigged ships, carrying 36 or fewer guns, usually all mounted on deck rather than below decks as in the great ships. Other small naval vessels of the 18th and 19th centuries included brigs, brigantines, schooners, cutters, and luggers. For present-day naval ships, see NAVAL VESSELS,.

American types.

Though gradually increasing in size and with minor improvements in detail, sailing ships remained unchanged in their essentials for the three centuries following Columbus's voyages. The renowned clipper ship, which brought a remarkable advance in speed, was introduced only near the end of the sailing-ship era in the mid-19th century. Its predecessor, the Baltimore clipper, which was developed around the time of the American Revolution, established an international reputation for swiftness and was particularly successful in blockade running and privateering during the War of 1812. Slightly modified and enlarged to accommodate up to approximately 450 metric tons burden, Baltimore clippers were used as fast mail and passenger packet ships in the transatlantic trade after the war.

The true clipper ships, which replaced the Baltimore clippers, were the highest development of the commercial sailing ship, combining speed and seaworthiness. Long, slender, and sharp-bowed, clippers excelled in long-distance commerce, such as the U.S.-China trade and the Britain-India trade. The trade between the west and east coasts, brought on by the California gold rush of 1849, accelerated the need for fast-moving ships. As a result, during this time numerous speed records were set.

The largest clipper ever built was the Great Republic, built in 1853 by Boston naval architect Donald McKay (1810–80), whose clippers set many of the records for transatlantic, New York-to-San Francisco, and around-the-world voyages.

Close of the Sailing-Ship Era.

American wooden ships, particularly the clippers, dominated all ocean trade until the depression of 1857, when the British took the lead in the construction of so-called composite ships, which were planked with wood over iron frames, and in the construction of iron ships. Ships of the composite type, such as the British Cutty Sark, carried a major portion of the ocean freight of the world until approximately 1900, but they were unable to compete with steamships for the premium rates offered for fast freight service. In the Australian grain trade with Great Britain, sailing ships were used as late as the 1920s. These sailing ships were often made of steel and were usually rigged as barques, because this rig could be sailed with a smaller crew than the ship-rigged vessels. For the American coastal trade, many large schooners were constructed and were used until shortly after World War I. These schooners had four or more masts, could carry large quantities of cargo because of their fore-and-aft rigs, and could be handled by a comparatively small crew. The largest of these schooners was the seven-masted Thomas W. Lawson, built in 1902, which was a steel vessel with a tonnage of well over 5000. See SAIL,; SAILING,.

STEAMSHIPS

The earliest recorded use of steam power in a boat was in 1786, when the American inventor John Fitch launched a small steamboat on the Delaware River. He obtained a speed of more than 10 km/hr (more than 6 mph) in his second steamboat, built in 1788. The American inventor Robert Fulton built his first successful paddle-wheel boat in 1807, and within a few years boats of this type were in extensive use on inland and coastal waters in both Great Britain and the U.S.

Early Developments.

The first steam-powered vessel to cross the Atlantic Ocean was the converted coastal packet ship Savannah, which sailed from Savannah, Ga., on May 24, 1819, and reached Liverpool on June 20. Various other boats subsequently made the Atlantic crossing, but regular service was not instituted until 1840, when the newly formed Cunard Line began and maintained regular service between Great Britain and the U.S. The ships used were wooden, paddle-wheel steamers that also carried masts and a barque rig for use when the wind was fair. Their two engines delivered a total of about 1500 hp and propelled the ships at about 9 knots. The first U.S. steamers to maintain a regular schedule across the Atlantic were the Hermann and the Washington, which went into service in 1847. Among the early attempts to apply the screw-propeller principle to the propulsion of boats was the construction in 1804 by the American inventor John Stevens of a twin-screw steam-powered boat. Although it had several successful trials, difficulties in manufacturing the engine discouraged Stevens from further experimentation. Introduced independently in 1836 by the Swede John Ericsson (1803–89) and the Briton Francis Smith (1808–74), the screw propeller was tried out in a number of vessels, notably the British vessel Great Britain, which was completed in 1844. The ship was 98.2 m (322 ft) in length and had a cargo capacity of almost 3550 metric tons. The single 2000 hp engine drove the ship at the rate of 12 knots. The Great Britain was wrecked on the coast of Ireland but withstood severe winds and seas for an entire winter and was later refloated without damage. This success removed much of the conservative prejudice against the use of iron as a shipbuilding material.

Evolution and Steamship Engines.

Further improvements in the propulsive mechanism of steamships included the introduction of the multiple-expansion engine. Early marine steam engines employed the single-expansion principle, in which steam from the boiler was introduced into the cylinders in which it expanded and was then exhausted. With improvements in boilers and an increase in steam pressure, engine designers found that they could use the steam exhausted from one cylinder to power another low-pressure cylinder, thereby increasing the overall efficiency of the power plant. Engines of this type, known as double-expansion engines, were later supplanted by triple-expansion engines that were still more efficient. The first double-expansion engine was used in 1854 and the first triple-expansion engine in 1873. The use of engines of this type removed one of the great obstacles to the further development of the steamship: the need for carrying an extremely large supply of coal for fuel or for refueling frequently during long voyages.

Other developments included the introduction of twin, and later triple and quadruple, screw propellers to minimize the danger of having a ship left helpless if a propeller or a propeller shaft broke.

Beginning in the 1890s experiments were made in replacing reciprocating steam engines with steam turbines. The disadvantage of the turbine was that it was inherently a high-speed mechanism, but this was overcome by installing a reduction gear between the turbine and the propeller shaft, thereby permitting the turbine to drive the propeller at an efficient slow speed. Turbine installations are standard in most modern steamers and are sometimes combined with reciprocating engines that operate on the same shaft. In many modern vessels, and particularly in warships, turboelectric drive systems have supplanted systems using mechanical drivers. A turboelectric power plant consists of a steam turbine driving a dynamo that, in turn, operates motors that turn the ship's propellers. Turboelectric drive is extremely flexible in operation and eliminates many of the mechanical difficulties of turning propellers through long heavy shafts.

By the late 1950s nuclear power plants had been developed to provide steam for the propulsion of both naval and merchant ships. The nuclear-powered merchant ship Savannah, built by the U.S. government, made a number of technically successful experimental voyages. Operating costs, however, remained higher than those of conventionally powered competitors.

MOTOR SHIPS

The development of the internal-combustion engine in the latter part of the 19th century, and particularly the development of diesel engines, made possible the design of power plants for ships that are far more efficient than any conventional steam plant. The use of efficient engines is especially important in shipbuilding, because engines of high efficiency permit the ship to carry less fuel and more cargo. The first motor ships, the general term for ships using diesel power, were constructed in the early years of the 20th century; they were comparatively small, but in the years following World War I a number of large motor-powered passenger liners were built and were operated with great success. Motor ships make up 76 percent of the world fleet of more than 43,000 vessels of 90,720 metric tons and over; slightly less than 75 percent of the fleet is diesel powered.

Surface-Effect, Captured-Air-Bubble, and Hydrofoil Ships.

In recent years a number of novel types of ships have been developed, all resulting from a constant search for faster transportation. The conventional ship is a displacement vehicle; it goes through rather than over the water when moving, thereby creating waves. Power is needed to overcome this wave-making effect and to overcome the friction between the skin of the ship and the water. At high speeds the power needed is enormous; for example, a 54,431 metric ton aircraft carrier must have 280,000 hp to drive it at 35 knots.

If a ship is lifted clear of the water, no waves are made and the ship is free of the frictional resistance of the water. Most recent shipbuilding developments try to free the vehicle from the surface of the water.

The surface-effect ship rides on an air cushion (see AIR-CUSHION VEHICLE,). Air is pumped under the ship by large blowers. The ship is actually lifted by this cushion of air and rides on it instead of in water. Skirts extend down into the water to keep the air cushion intact. Wave making is eliminated, and frictional resistance to the water is very small, so that it is possible to attain high over-water speeds with relatively small propulsive power. Ships of this type as large as 145 metric tons in weight have been built, and speeds higher than 100 knots have been reached by smaller craft. The true surface-effect ship is also capable of “flying” over smooth ground.

The captured-air-bubble ship is a variation of the surface-effect ship. It rides partly on air and partly in water. Air is pumped in at the bow and “captured” by a hinged skirt. As the ship moves through the water, part of the weight of the ship is supported by the bubble of air and the rest by water. This device helps to reduce both frictional and wave-making resistance and thus to increase the speed. The captured-air-bubble principle has been used successfully in small craft.

The hydrokeel is somewhat similar to an air-supported ship. A relatively small fan is used to keep a thin sheet of air under the ship. The sheet of air acts as a lubricant and decreases the frictional resistance of the water. This principle has proved practical in small craft with flat bottoms, but no tests have so far been made with larger ships.

The hydrofoil ship operates on principles altogether different from the air-supported group. In these ships, underwater planes, or foils, are connected to the ship by struts and, working exactly like airplane wings, lift the hull from the water. As the ship increases its speed, it moves free of the water surface, supported by the underwater foils. The foils may be partly above and partly below the water surface; consequently they are called surface-piercing foils. The faster the ship moves, the smaller the amount of foil that is underwater. The surface-piercing foil is the simplest kind of hydrofoil; it is extensively used on passenger boats and small ships plying the rivers and canals of Europe. The lifting foils may be entirely underwater, in which case they are called submerged foils. The lift they provide is controlled by the angle of the foils and the speed of the ship. Speeds of 100 knots and more have been reached with hydrofoil ships.

Container Ships and Tankers.

Two recent innovations in ship types have greatly influenced commerce, although the ships themselves are not technically remarkable. Container ships carry standard-size (6 m by 2.4 m by 2.4 m, or 20 ft by 8 ft by 8 ft) aluminum-alloy containers into which a wide variety of cargo can be packed. Economies include smaller dock labor costs, quicker turnaround time, reduced pilferage, and more efficient transfer to land transportation.

Tankers, built to carry the enormous petroleum traffic of the post–World War II era, are extremely simple in design. Machinery is concentrated at the stern and virtually the entire hull forward of it is devoted to compartments for liquid cargo. Because tankers move simply from oil source to receiving terminal, usually repeating the same voyage many times, crews are small, and much of the ship's machinery is subject to automatic control. The ease of tanker construction has led to a great increase in size; many tankers of several hundred thousand metric tons now ply the oceans, dwarfing the largest ocean liners.

SHIPBUILDING PRACTICE

Structurally, a ship is a hollow beam subjected to severe bending and twisting as it moves through waves and as its own load changes. The principles of ship structure and the nomenclature of its parts have long been established and are essentially the same whether the ship is a wooden sailing ship or a large modern tanker. The backbone of all ships is the keel, a longitudinal beam or girder located at the very bottom of the vessel and extending from bow to stern. At the forward end of the keel is attached the upright or nearly upright stem that forms the front of the vessel. A similar sternpost is usually set at the after end of the keel. The ship is given its shape by a series of symmetrically curved ribs or frames that run transversely and that are fastened to the keel at their centers. At and near their centers on the bottom of the ship the frames are made considerably larger than at the sides and are known as floors. The ribs are held in position by longitudinal stringers, or clamps, that run the full length of the ship and that are curved to conform with the shape of the hull. Additional bracing is provided by beams extending across the width of the ship and fastened at either end to the opposite sides of the ribs. In very small vessels only one set of beams, set at the ends of the ribs, is used, and these beams serve as supports for the deck. In larger vessels, several series of beams are employed, the number corresponding to the number of decks with which the ship is provided.

The skin of the vessel is mounted outside the frame. In steel vessels the skin consists of a number of metal plates riveted or welded to the frame, and in wooden vessels it consists of a number of horizontal planks called strakes. The term strakes is also sometimes applied to individual rows of steel plate in a metal hull. Transverse walls of wood or metal plate, depending upon the type of vessel, run from one side of the ship to the other at several places in the length of the hull. These walls, called bulkheads, stiffen the frame and often are used to break the hull up into watertight compartments as a safety measure, so that a leak in the hull will flood only part of the ship and sufficient buoyancy will be maintained by the other compartments to keep the ship afloat.

A number of modifications of the standard method of ship framing have been devised, particularly for use in tankers. Many tankers use a system of longitudinal framing in which a comparatively small number of large transverse frames is employed and the chief framing members are longitudinal and run the full length of the ship. The interior of the tankers built on this system is divided into a number of compartments by a longitudinal bulkhead running the length of the ship at the centerline and by a number of transverse bulkheads. The longitudinal system of construction has been applied to other forms of cargo vessels as well as tankers.

Construction.

The actual construction of any type of ship, whether made of wood or metal, is complicated by the various curves of the hull, the compound angles formed by the joints between the various structural members, and the necessity of producing a hull that is absolutely symmetrical and “fair” (having regular curves and surfaces that are smooth). Because of these requirements, it is almost impossible to build any form of ship directly from small-scale plans, as is done in the case of other kinds of structures. Instead the shipbuilder, before beginning work, must resort to the practice of lofting, or laying down, the lines of the ship.

Lofting consists essentially of preparing in full size an exact skeleton plan of the hull to be built. From this plan the builder determines the dimensions and forms of the frames and plates, which, when assembled, make up the ship structure. The entire plan of the ship structure is laid down on the flat floor of a special room or building known as the mold loft. Paper or wooden patterns, called templates, of the pieces of the hull are then constructed from this plan and are used in the building shops to cut and form the plates and frames to the required configuration. The more complex the ship, the more detailed are the loft templates. Although the principles of lofting have remained unchanged for centuries, specific techniques have been improved in recent decades. The skeleton plan, instead of being laid down full size, is prepared with great precision to small scale, typically one-tenth of full size. Templates are taken from this plan and photographed, resulting in transparencies less than one-hundredth of full size. The transparencies are either projected onto an uncut piece of construction material and the piece marked off, or the transparencies are used directly by automatic cutting machines. For many parts of the hull, computers may be used to describe the space of the part and the description may be used to control the cutting machine directly.

Building Wooden Ships.

As mentioned earlier, the general structural details of wooden ships are the same as those of steel or iron ships, but the methods of construction differ somewhat because of the difference in the nature of the material.

The method of wooden shipbuilding called sawed-frame construction is essentially similar to the construction of steel ships. Wooden frames pieced together of a number of sawed pieces of wood are mounted on a heavy keel timber, are suitably braced, and are then covered with the hull planking. In bent-frame construction, the frames are set in place after the shape of the hull has been formed in the following manner. A number of heavy molds are set up at regular intervals along the keel, representing the cross section of the ship at those particular points. A number of comparatively light planks or strips of wood running in a longitudinal direction are then bent around the outsides of the molds to form a kind of outer skeleton of the hull. These “ribbands” are then used as a form inside which the wooden frames are bent into shape. The frame timbers are steamed or soaked in hot water until pliable, and then they are bent to fit the curves that are formed by the ribbands.

The outside of a wooden ship hull is finished by planking that, like framing, is done by several different systems. In carvel planking the separate boards, or strakes, are laid edge to edge to form a smooth surface, and the seams between them are caulked to make them watertight. In lapstrake, or clinker-built, planking the boards of the hull are arranged so that the edge of each board slightly overlaps the one below it, like the siding of a clapboard house. In most forms of planking the boards run horizontally from the stem to the stern, but in hulls that are double-planked for extra strength it is common practice to run the planking of the inner skin diagonally and that of the outer skin horizontally.

Building Steel Ships.

For many years the processes of ship construction were essentially the same throughout the world. The flat plate forming the keel was laid on blocks, and a longitudinal girder was attached along its centerline. This girder serves to make a space between the outer shell of the ship and the inner plating of the hold, thus providing a double bottom that adds strength and serves as a storage tank for fuel oil or for water used as ballast to trim the ship. The plates and beams that form the individual frames were then cut and bent to shape according to the mold-loft templates. The frames extended from either side of the keel and vertical girder to the top of the sides or the gunwales of the ship. The deck beams that reach from gunwale to gunwale and hold the tops of the frames together were erected, and the steel plating that covers the sides and decks was fastened in place. Then the inner structural members of the hull were set in place and fastened.

In recent years major changes in shipbuilding processes have been made possible by welding instead of riveting parts together and by using cranes that can lift, transfer, and place very heavy weights, as much as 725 metric tons. The parts of the ship remain the same, but they are assembled into large subsections or blocks in the shop, not on the building ways or the erection dock. The size of the sections is determined according to the best use of shipyard equipment. Often they are built upside down to facilitate the fastening of the parts together. Often the machinery and piping for each subsection are fitted in place during shop assembly. The subsections are then moved to the building ways or the erection dock and fitted together. Thus, much of the work on the ship can be done in several locations at the same time. The ship may be assembled on building ways or in a dock. In the latter case, when the hull is completed, the dock is flooded and the ship floated out. Docks are used in the assembly of all very large ships. Most other ships are assembled on building ways. The ways are on ground above the edge of the water and slant toward the water. When the ways are at right angles to the edge of the water, the ship is “end-launched.” When the water is narrow, the ways may be parallel to it; in that case the ship is “side-launched.” The ways consist of two sets of heavy timbers: the fixed ways, which extend on either side of the ship from the point of building to below the high-water mark, and the movable ways, which slide on the fixed ways and support the weight of the ship by means of an elaborate wooden cradle. The fixed and movable ways are firmly fastened together so that the ship will not move on the ways until the moment for launching arrives.

When the ship is ready for launching, the cradle is set in position, the keel blocks used during building are removed, and the surfaces of both the fixed and movable ways are heavily lubricated. At that time the spikes or other fastenings holding the ways are released and the ship slides down into the water of its own weight. The construction of ways and the launching of ships, particularly large ones, are precise and delicate operations. After the ship has been launched, its construction is finished while it is moored at a pier. The final processes before launching depend on the extent to which the ship is completed; a ship can be complete in all respects except testing before it is launched. Usually, however, after launching, the final equipment is installed, the equipment is tested, and the ship is delivered to the owner.

SHIPBUILDING STATISTICS

In 1990 the total gross tonnage on order or being built throughout the world amounted to about 41.6 million. Over 36 percent of the world tonnage was to be built in Japanese yards. After Japan, in order of percentage, were South Korea, Germany, Denmark, Yugoslavia, Italy, Spain, Brazil, and Poland. Construction of merchant vessels in the U.S. declined drastically during the 1980s. By the end of the decade, the value of work performed at private U.S. yards was about $8.5 billion annually; naval vessels accounted for virtually all new construction.        H.I.C., HOWARD I. CHAPELLE

For further information on this topic, see the Bibliography, sections 557. Ships–558. Boats, 561. Naval vessels.