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SHIPBUILDING  ninth and the United States about one eleventh. Of our steamers about half are built in ocean-ports for ocean-trade, and about one half in lake ports for lake-shipping. Of all sailing-vessels England owns about one fourth, the United States about one fourth and Norway one eighth. There are few large sailing-vessels on the American lakes. The average size of steamers is about 1,600 tons; of sailing-vessels 580 tons. The average size of vessels has increased three and a half times in the last 30 years. Steam-vessels are constantly taking the place of sailing-ships, and steel-ships of iron and wooden ones.

The United Kingdom builds about 1,600,000 tons each year, including warships. This total is about two thirds of all the tonnage produced. The United States builds about 400,000, Germany about 300,000, and France about 100,000 each year. Of the states in the Union, in iron and steel shipbuilding Pennsylvania easily leads, with New York, Maryland and Michigan following. In building wooden ships, a much less important industry, New York leads, with Maine, New Jersey, California and Washington following. In 1909 the value of the products of shipbuilding plants in the United States was $73,360,315, to which should be added $25,872,033 as the value of the product of the Federal government's establishments.

As regards material, the advantage of steel and iron over wood is, first, in weight; iron saves 30 to 40% in weight compared with wood, and steel nearly 15% compared with iron. Second, as regards safety, steel-ships are far safer than iron or wooden ships, largely because injuries from collisions etc. do not spread so extensively. As regards convenience in manufacture, steel is easier to work when cold than iron, and can be cast or rolled in larger sizes, for many parts of the ship. Both these materials enable a machine to manufacture and substitute one piece in many portions of the ship, where, in a wooden vessel, the carpenter must carefully fit together many pieces. The single disadvantage of the metal ship is its greater tendency to become covered with sea weed etc.—that is, to “foul.” In consequence it must resort much more often to the docks for cleaning.

Shipbuilding once was a trade and an art. It now is an industry in which many trades are combined, from boiler-making to electric-wiring and from the calculation of the strains to which the several parts will be submitted to the decoration of the splendid furniture of the finished ocean-liner. Again, it is a science rather than an art, inasmuch as the builder is guided, not so much by the image and the actual sight of the ship, as by a system of rules and by pages of calculations.

The best ships are built double-bottomed. The keel is laid, and then the bottom is built of a number of cells or steel-boxes. One or more longitudinal bulkheads run the length of the ship. Steel frames take the place of the old wooden ribs, and are so shaped as to connect readily with the other parts of the ship. Plates of the required sizes and shapes are then brought, riveted and calked. The rivets are brought red-hot, placed through holes bored in the plates, and then hammered out so as to stay. As they cool, their grip fastens. Calking is done by hammering a chisel-shaped tool against one plate where it overlaps the next one. The great length of our modern ships is made possible by a truss-construction, not unlike that employed in many steel-bridges. The best ships are divided into many watertight compartments, such that two or more may be filled without causing the ship to sink. These compartments naturally add still more to the strength of the ship. It is common to use the double-bottom to admit water as ballast, where the ship has a light cargo. In simpler ships the frame or rib joins directly to the keel.

Vessels are usually launched when the hull is sufficiently advanced to assure its floating, so as to diminish the weight to be handled in launching. A cradle is commonly built around the ship, which is of wood, and rests on smooth, wooden “ways” which are lubricated with soap etc. These support the vessel beneath and at the sides. The keel rests on blocks, which also support the ship out towards the sides. When these blocks are knocked away, the weight of the ship is transferred to the cradle and to the ways. As these have a slope of about five eighths of an inch to a foot and are well-greased, the ship has only to be released from restraint to start with increasing velocity towards the water. It is at the moment when the restraints have been removed, after the blocks have been knocked away that the ceremony of “christening” the ship commonly takes place. Once the vessel is afloat, the machinery and, if it is a warship, the armament are put in, and the furnishings of the ship are completed. In the case of a modern ocean-liner the rooms are decorated as in the richest hotels.

Many enormous cargo-ships have been built, of which The Oceanic of 28,000 tons is an example. These ships have steam or electrical hoisting-engines on their decks, and the masts serve as derricks in port and as signal-posts at sea. Sails they never bear. Oil is shipped in tank-steamers, and wheat-ships have special forms of construction to make the unloading and loading easier.

Most large vessels are now built with two and even more screws. This enables the 