intercostal, with a rider plate on top as shown. Below the protective deck, before and abaft the machinery space, the frame is formed as shown in Fig. 28, with a 4-in. zed bar connecting on to a 10-lb. (4 in.) floor-plate. Above the protective deck the frame is formed of a 4-in. zed bar. Sloops.-A large number of small vessels, about 1000 tons displacement, called sloops, are employed on foreign stations. They carry some sail-power, and are sheathed with wood and copper for the reasons given above. COAL COAL WL A section of such a ship is given in Fig. 29. One feature of these vessels is the absence of any protective deck. In the side bunkers, however, there is a division, at about the level of the waterline. It is intended that the coal should remain in the upper part of the bunker as long as possible, in order to serve the purpose of protection, and to assist in preserving the stability if the side were pierced. FIG. 29.-Sheathed sloop. These ships are framed on the transverse system with the frames 24 in. apart. Below the watertight division in the bunkers a frame bar, 4 in. x 3 in. (Fig. 30), is worked from side to side. Between the coal-bunker bulkheads a floor-plate is worked, 10 lbs. (in.), with a reverse bar, 3 in. x 23 in., on the upper edge. A 3 in. x 2 in. reverse bar is connected to the frame bar above the bulkhead. Above the bunker division the frame consists of a 4-in. zed bar. It will be noticed that the bunker division severs the transverse frame completely, and to maintain the continuity of the transverse strength bracket plates are worked as shown. The middle line keelson (Fig. 30) is formed by an intercostal plate, 15 lbs. (in.), between each pair of frames, with staple angles, 3 in. x 3 in., connecting to the flat keel and to the floors. The intercostal plates project above the floors and connect to two continuous angles, 3 in. x 3 in. An intercostal keelson is also worked on either side. Torpedo-boat Destroyers.-The essential feature of this type of vessel is speed, and every effort is made by careful design, high quality material and careful workmanship, to keep down the weight of the hull structure to the lowest amount possible. Sections of a typical destroyer are given in Figs. 31 and 32 the first showing the transverse portions of structure, and the second those portions which give longitudinal strength. The ship is framed on the transverse system with a frame, floor, and reverse frame. Deep frames are fitted at intervals. There is a middle line intercostal keelson with continuous angles at the top and bottom. The engine and boiler bearers are so arranged as to assist materially in providing longitudinal strength to the structure. Flanging of plates is largely adopted to save the weight of connecting angle bars. The deck is of special importance, as it is severely strained if the ship is subjected to a sagging moment. In this case the deck between the beams is liable to buckle, being of thin plating, and in order to enable it to effectively stand the strains, it is well stiffened by fore-and-aft girders. Deep beams are fitted at intervals. WL CHAPTER IV. BEAMS, PILLARS, AND DECKS. Beams. The transverse framing we have been considering ends at the upper deck. To complete the transverse structure we have beams connecting the sides of the ship together at the level of the various decks and platforms. Beams not only tie the sides of the ship together, but they form the support to the decks and platforms. Beams for decks on to which water is likely to come, as the upper and main decks, are made with a round down in order that the water may run to the side scuppers. The amount of this round is 9 in. in a 75-ft. battle-ship, and 6 in. in a 40-ft. cruiser. Beams to the lower protective decks are of the same shape as the deck, usually level at the middle line and sloping down to the sides (see Fig. 12). Beams to the lower platforms and decks are level (see Fig. 19). Beams in a large ship are spaced every 4 ft. where the frame spacing is 4 ft., and every 3 ft. at the ends of the ship. For a small cruiser the beams are placed on alternate frames, i.e. every 4 ft. Beams are most commonly formed of angle bulb (c, Fig. 8). Most decks are now covered with steel plating, and the angle bulb is then a convenient beam to use. When, however, a wood deck has to be laid direct on to the beams, as is sometimes the case, it is more desirable to have the tee bulb (d, Fig. 8), in order that the deck bolts may be worked zig-zag, and not in a direct line, as would be the case with the angle bulb. The tee bulb is a convenient form to use for skid beams for supporting the boats. A zed bar (e, Fig. 8) is a convenient form of beam when the flat supported forms the crown of a magazine in which teak lining is fitted. The lining can be bolted to the inner flange of the zed. In recent ships, however, the lining to magazines has been dispensed with, so that this form of beam is not MAIN DECK TWD 15 LB THICKNESSES 00 17/% 10 MIDDLE DECK, I. BEAM 20 LB BRACKET 6 INCH ZED 15 LB BRACKET 10 INCH 4 TEAK BACKING PLATE FRAME FIG. 34. necessary. Angle bars are used as beams to flats in which the greater strength of the angle bulb is not required. The connection of beams to the transverse frames is of great importance, as this, together with the transverse bulkheads, helps to prevent the racking of the ship due to rolling. To ensure an efficient connection, the beam is connected to the frame either by a beam arm, or a bracket plate. The beam arm is used where a neat appearance is desirable, as below the upper deck. To form the beam arm, the beam is cut at the middle of the |