SHIPBUILDING. The development of shipbuilding is represented in its main stages by the evolution of the hull and the introduction of the machinery of pro pulsion. The first carries us back almost to the prehistoric period and to an idea as simple as the floating log. The line of development through the raft, the hollowed-out trunk, the boat of skins stretched on frames, and the vessel of planks tied together brings us finally to the wooden and iron ship of modern times. From very early times the idea of the oars and the sail had already been evolved. Early Egyptian drawings show vessels of sawn planks with sails and oars. The Greeks and Romans enlarged the size of their vessels, but they still remained dependent on man-power. In medie=val times Irish mariners sailed in vessels propelled by sails and oars to the Faroe Islands and Iceland, which they discovered, and Columcille at Iona com manded fleets of vessels which passed constantly between Iona, Derry, and other Irish ports. Ships remained dependent on sails and man-power for propulsion down to modern times, but the arrival of steam engines resulted in a general awakening of the possibilities that lay in natural forces and shipbuilding, like other mechanical arts, took an upward bound. The general shape of vessels had to be modified to the new methods of pro pulsion, and gradual perfection was reached. Attention was given in the changed circumstances to greater stabil ity and speed, simplicity was sought in the mechanical apparatus, and the struc tural arrangement was developed to se cure greater habitability. The substitu tion of iron for wood and of steel for iron had reference not merely to increased resistance and durability and safety from combustion but also to the reduction of weight of hull in proportion to weight of lading. The investigation of the effect
of the shape on buoyancy, speed, range of stability, and righting ability resulted in a certain standardization which has elim inated former dangers, so that safety at sea is now as procurable as on land. The naval architect drafts his plans on paper, and embodies parts of the vessel in wooden models. Molds are then laid by the constructive force. When these are completed actual construction begins with the preparation of the building way along keel blocks. On these the keel is laid, in sections, riveted together and fastened to the stern and stern posts. The midship frames are then set up, being held by a vertical internal keel till the forged stern and stern posts and the com plementary plating are put in and the form of the ship is completed.
Affer the launching the machinery is put in and the interior supplementary fittings are added. The reciprocating engine long held the field, but in recent years the development of turbine engines displaced the older type while the use of oil and the Diesel engine has produced motor vessels of the largest displacement as the latest type of all. The enormous expansion in shipbuilding has now also entailed the introduction of an immense variety of auxiliary machinery and ap pointments so that a modern transatlan tic liner has come to partake of the char acter of a floating city. The building of naval vessels is, of course, differentiated from the building of passenger and cargo ships in many essential ways, but the actual ship is fundamentally the same, and the differences lie in the purposes of the parts, such as machinery, guns, and armament, added to it. See SHIPPING.