Materials Used in As the development of naval architecture has been largely influenced by the materials used in ship construction, brief allusion to these materials seems appropriate. The material used in the construction of ships underwent, broadly speak ing, two changes during the 19th century; a change from wood to iron, which dates approxi mately from about the middle of the century, and a change from iron to mild steel, which dates from about 1880. Wood is still used as material for shipbuilding, U many coasting ves sels, for instance, in the United States and else where being still built of wood; hut the number and importance of wooden ships as compared with those of iron and steel is diminishing yearly, and, at the present date, it may be said that the only structural material of importance for the construction of ocean-going ships is steel. Open-hearth steel, suitable for ship building purposes, with an ultimate tensile strength of about 60,000 pounds to the square inch and an elongation of an 8-inch specimen of from 20 to 25 per cent before rupture, was introduced between 1870 and 1880. It was practically unknown in the United States in 1880. The contractor for the first steel vessels of the new navy, which were contracted for in 1883, had to make special arrangements for the domestic manufacture of the steel needed in his work, and had to pay for it at that time about seven and one-half cents per pound. The growth of the manufacture of this material in the United States since that date, however, has been astonishing, mild steel of nearly the same characteristics as that used for ships being used in large quantities for bridges, houses and other structures, to that, about 1900, its price had fallen as low as one and cne-half cents per pound, as compared with seven and one-half cents per pound some 15 earlier. The qualities of the steel used in shipbuilding vary little in the different ship building countries, being prescribed, as a rule, for merchant ships, by the marine insurance societies. For men-of-war, a somewhat higher grade of material is prescribed, and the inspec tion is rather more rigid. The use of nickel steel, too expensive for commercial vessels, but very superior for armor plates and guns, gives an added strength of 30 per cent over open hearth steel. It retains its fibrous struc ture under strains and shocks where carbon steel crystallizes and crumbles. Coincident with the development of iron and steel as materials for shipbuildh4, there began to develop an in crease in the size of ships, due to the greater strength of the material of construction, and probably also to the fact that the use of steam instead of sails for propulsion made it possible to increase the propulsive steam power of the large ships when it would not have been pos sible to add correspondingly to their sail area. The tendency toward an increase in size has been very marked since 1885, until now ships have reached sizes and dimensions limited only by the draft of water and the docking and wharf facilities available in the ports to which they trade.
The urgent necessity of quickly replacing the shipping destroyed by the German sub marines, while it did not and could not alter the basic principles of naval architecture, called for adaptations which departed widely from the practices of the period preceding the Great War. The lack of shipyard facilities and of highly trained shipbuilders led the men in charge of the government program to enlist the structural iron workers of the in the great problem of producing ships. The °fabricated ship° thus came into being. designed in such fashion that its parts could be con structed by the makers of steel bridges, tanks and frames for skyscrapers. Wherever angles could take the place of familiar bends and curved surfaces the change was made, and quantity tonnage was thus expedited, although the new models were less speedy than the more scientific hulls of former years. The structural
shops were able to do nearly all the punching, shearing and bending of the plates, and only the assembling and rivetting and the expert fashioning of how and stern was done in the shipyards. Another effect of the emergency was the standardization of types of vessels to he built. When the Shipping Board began its work there were many different types of vessels under construction in the shipyards of the country. The government representatives speedily recognized that much labor was lost in this diffusion of effort and a few types were selected and all agencies concentrated on the utmost possible production of these typical ships. The standard cargo vessel was a single screw steamer of 9,600 tons deadweight, 395 feet in length, 55 feet molded beam and 34 feet molded depth; the engines, geared turbines of 2,500 horse power, and the fuel, oil. Another type was the combined passenger and cargo vessel, arranged for use as a troopship, carry ing' 2,700 troops and 7,000 tons of supplies. This type with a displacement of 20,900 tons was 522 feet in length, 62 feet beam and was equipped with twin screws driven by two sets of four cylinder triple (xpitte,ion reciprocating engines. Its speed was 14 knots which could be increased to 15 knots in emergencies. Another selected type was the 10,000-ton oil tanker, 435 feet long and 56 feet beam, equipped with a single screw, triple-expansion engines and oil-burning boilers. A revival of wooden ships resulted in the production of 3,600-ton vessels, 286 feet in length and 46 feet beam. A partic ular type of architectural design gave them the title of aFerris after their designer. While not wholly a development from war con ditions the production of the Diesel ships was stimulated by the demand for ocean tonnage, and these, too, were standardized in the interest of rapid multiplication, the selected type being of 9,600 deadweight tons with turbine engines driving twin screws. The compactness of the Diesel engines gave these vessels the advantage of 13 to 14 per cent larger carrying capacity for an equal displacement, and operated with a smaller crew and at a higher comparative speed. Another architectural development was the re inforced concrete ship, successfully built up to 3,500 tons, and with designs approved up to 7,500 tons. The fact that only $60,000 worth of steel was needed in a 5,000-ton concrete ship as compared with $300,000 worth in an all-steel ship led to earnest effort in this direction. A special form of concrete lighter than wood and impervious to water was developed by the archi tects in charge, and the completed ships were found to be unusually free from the vibration common to all-steel vessels. Composite ships of wood and steel were also planned and built to meet the emergency caused by the war.
The present state of development of naval architecture is probably best illustrated by ex amining the characteristics of some of the most recent products of shipbuilding skill in this country as exemplified in the principal char acteristics of the United States battleship Idaho, commissioned in March 1919, and the new troop ships mentioned above, which are representative of our latest American designs. Commercially, it is found that the large steamer will carry freight or passengers cheaper at the same speed, or faster for the same cost, than the small steamer. The large man-of-war, on the other hand, is able to carry a much greater weight of armor and armament and can maintain a higher sustained sea speed than is practicable in a ves sel of small displacement. See WARSHIPS.