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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.
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.
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.
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 (now divided into Croatia, Slovenia, Bosnia and Herzegovina, the Former Yugoslav Republic of Macedonia, and the Federal Republic of 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 $8.5 billion annually; naval vessels accounted for virtually all new construction.
Contributed by: Howard I. Chapelle
"Ships and Shipbuilding," Microsoft® Encarta® 97 Encyclopedia.
© 1993-1996 Microsoft Corporation. All rights reserved.
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Last Revised: November 20, 2008 06:57 PM.
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