- SHIP B (=DING. The most essential con ditions in the construction of a ship are, that it be capable of carrying its stores and its artillery or lading ; that it be moved by wind or steam with great velocity, and that it readily obey the motion of the rudder ; that it have the necessary stability, so as not to be overturned when acted upon by the wind or waves ; and finally, that its rolling or pitching be attended with as little strain as possible on the timbers. In merchant ships an ample capacity is fre quently of more importance than a great velocity in sailing. In ships of war the num ber and weight of the guns constitute the basis of the design; for from these the weight of the whole ship, or the volume of the water which it will displace, may be estimated. The draught of water (the depth to which the ship is immersed) may depend on the depth of water in the harbours and roadsteads ; but it must also be determined from experience, so that the ship may be prevented as much as possible from making leeway. Finally, the form of the body must be that which is most favouratle for velocity, by causing the least possible resistance of the water at the bows and along the sides ; which allows the greatest lateral resistance, and which will permit the rudder to act with most effect in causing the ship to be turned about a vertical axis. Ex periments have shown that when the quantity of sail is the same, the velocity of a ship is increased by increasing the ratio between its length and breadth.
It has been found that ships having the same proportions possess unequal sailing properties ; it may be perceived indeed that a small ship built according to the proportions of a large one which is know to sail well, will not possess the like good quality; so that the sailing qualities depend on something more than mere form. That a ship whose hull has been constructed according to the best rules of art does not always fulfil the conditions re quired, may depend on several causes. The blocks, ropes, &c., may be too heavy, and the sails may be badly formed; or the burden of the vessel may be unskilfully distributed.
In building an ordinary ship the draughts man draws a plan analogous to that of an architect in building :a house; the drawings re present the intended vessel in many. points of view—not only as a whole, but in respect also to the curvatures of the various timbers. Thin pieces of lath are cut and marked so as to assist in determining the proper sizes and shapes of the timbers. For a large East India man there are upwards of 100 of these mould ing pieces (as they are called) prepared. The oak and elm trunks are then cut up to the proper forms for the timbers, by sawing, the moulding pieces serving as guides. All being cut and prepared, the building of the ship commences. The keel, which is formed of elm, is scarfed together very strongly. The stem and stern-posts, of oak, are raised and fixed at the two ends of the keel; and various pieces called transoms, fashion pieces, &e., help to give form to the two ends of the ship. Stout timbers, called floor timbers, are laid athwart the keel ; and around them solid wood, called dead wood, is packed in, to form a solid foun dation. Then come the ribs of the ship, which
are the curved oak timbers bending upwards and outwards from the keel to the top ; these are formed of several pieces called fatiocks or foothooks, which are securely bolted together. These various timbers are strengthened with inner timbers, called the keelson, stemson, sternson, riders, &c. All the outside is covered with oak planking, varying from three to six inches in thickness, and arranged in parallel rows called strokes. The filling up the inter stices between these planks has been noticed under RIGGING. The beams are timbers of great strength, to support the deck, and to bind the sides of the vessel together; while the knees are immense brackets which support the ends of the beams. The decks are formed of Dantzig fir or yellow pine, laid in boards from six to ten inches in width, and from two to four in thickness. The treenails are the oak pins or bolts by which the planks are fastened to the timbers of a ship. [TuenNims.] The sheathing of ships at first consisted of a second covering of planks applied on the exterior of the first, over the bottom and sides as far as they were under water ; but this being found to impede the motion of the ship, a sheathing of milled lead (the invention of Sir Philip Howard) was subsequently em ployed. The application of plates of copper as a covering on the exterior of ships was first tried in 1760; and in 1783 all those belonging to the royal navy were ordered to be covered or sheathed with that metal. By this practice shells and sea-weeds are prevented from ad-. hering to the sides and bottoms ; the friction of the water against them is diminished, and i the damage which would be caused by worms is avoided. Owing to the great expense o copper sheathing, which has the effect o limiting its use in mercantile shipping, man; attempts have been made to substitute for i either other metals, or alloys in which it it mixed with cheaper metals, such as lead, oi with such as might increase its durability, at zinc. Iron, protected by the galvanic tidier of zinc, has been used. Sheathing of brows paper, coated with tar, and a kind of felt, int( the composition of which a considerabh quantity of cow-hair enters, have also beer tried. Copper sheathing is usually applied it sheets about 4 feet long and 14 inches wide the thickness being such that a square fool weighs from to 32 ounces, but most com monly from 20 to 28 ounces; and the mode of application does not vary materially whether the copper be laid upon the bare planking or upon an interposed layer of tarred paper, felt, or thin boarding. The sheets are pierced with holes, not onlyround the edges, but also at intervals of 3 or 4 inches over the whole sur face ; they are laid so as to overlap each other about an inch, and are secured to the ship with flat-headed copper nails. An East India. man requires re-coppering after two voyages ; and the old copper is found to have lost three or four ounces of its weight in the square foot, by the action of sea-water, friction, and other causes.