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Ships and Shipbuilding, the types and construction of any large buoyant type 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.
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 (m ore 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 United States.
The first steam-powered vessel to cross the Atlantic Ocean was the converted coastal packet ship Savannah, which sailed from Savannah, Georgia, 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 and the Briton Francis Smith, 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.
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.
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.
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.
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.
Contributed by: Howard I. Chapelle
"Ships and Shipbuilding," Microsoft® Encarta® 97 Encyclopedia.
© 1993-1996 Microsoft Corporation. All rights reserved.
Last Revised: November 20, 2008 06:53 PM.
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