CHAPTER XXIX. TRIPLE-EXPANSION ENGINES, S. S. "COLUMBIA," 12,000 I. H. P. (ENGLISH.) THE screws are revolved by two sets of engines, each set capable of developing 6,250 horse power. The cylinders are 40, 66 and 101 inches in diameter, stroke 66 inches. They are carried on extremely massive double-legged box columns. The bed plate and columns are unusually strong; in fact, it is not difficult to see that all the machinery is of dimensions very much in excess of that actually required. The wisdom of this was well illustrated when these enormous engines were running at full speed. Steel is freely used in the moving parts of the machinery. The reversing gear is very rapid and noiseless in its action. The shafting is of steel, and is hollow. The crank shaft is 202 inches diameter, the tunnel and propeller shafting being 191⁄2 inches and 201⁄2 inches in diameter respectively. The thrust-block is unusually large, and is of the adjustable open "horseshoe" patent. The glands in the engines are packed with metallic packing, and throughout the long trip, with the engines at full speed the whole time, all the glands not only remained tight, but the piston and slide rods were as bright as possible, and no trouble was experienced on this head whatever. The slides for the H. P. and I. P. cylinder are of the piston type, and in the L. P. cylinder the long D slide is fitted with a balance back. All the slide rods are balanced. The slide valves are worked by the ordinary link motion of the single bar type. Tail end piston rods for the cylinders are not fitted, but the shoes on the piston rod heads and the guide plate of the column are given very large surfaces. The pistons themselves are very deep. Condensers are placed at the back of the engines, and are of the usual surface pattern. The air pumps are driven by a rocking lever off the H and L cross heads. These are the only engines driven in connection with the main engines. Bilge feed and each circulating pump are driven by a pair of independent engines, made to a special design. There are two three-bladed steel propellers, their diameter being 18 feet and 32 feet pitch. The total blade area is 96 square feet, and the total disk area is 509 square feet. The bosses are of steel, and are 4 feet 6 inches in diameter. There are 9 boilers, in three groups of three each, and each group, together with its coal supply, is placed in a separate water-tight compartment. Six of these boilers are 17 feet 3 inches long, and 15 feet 4 inches diameter, and |