Cruisers 12 and 13* of 1,000 Tons, and Naval Academy Practice Vessel. The machinery of these vessels is similar in all details. They will be propelled by twinscrew, vertical, triple-expansion engines, placed in a common water-tight compartment. The two sets of engines are independent, except that there is only one condenser for both. An auxiliary condenser with a capacity equal to all the auxiliary machinery, except the main air and circulating pumps, is to be supplied. This will have an independent, combined air and circulating pump. The main condenser will have airpumps and a circulating pump similiar in general features to those for the Monadnock. The valves for the H. P. and I. P. cylinders will be plug pistons grooved, one for the H. P. and two of the same size for the I. P., while the L. P. cylinders will have double ported slide valves, all worked by Stephenson double-bar links. The boilers will be of the low cylindrical type, all in one water-tight compartment. Evaporators, distillers, auxiliary machinery, etc., are provided as in the larger ships. Provision is made for heating the feed water. The following are the dimensions of the machinery: For cruisers 12 and 13, cylinders, * See drawings. Figs. 73, 74, 75, 76. 154, 222, and 35 inches diameter by 24 inches stroke. I. H. P. 1,600 at 200 revolutions per minute and 160 pounds working pressure. Piston-valves for H. P. and I. P. cylinders, 7% inches diameter. Diameter of crank-shaft journals and crank-pins, 7 inches, with 31⁄2-inch axial holes. Cranks at 120°, and sections of shafts interchangeable. The line, thrust, and propeller shafts will be about 7 inches diameter, with 31⁄2-inch axial holes. Cooling surface in main condenser about 2,246 square feet. Diameter of air-pumps 131⁄2 inches, stroke 12 inches. Capacity of circulating pump 3,000 gallons per minute. There will be two boilers 9 feet 9 inches in diameter by about 16 feet 10 inches long, with three corrugated furnaces of 36 inches diameter in each. Thickness of boiler shells seveneighths inch. Total grate surface, 100 square feet; total heating surface, 3,630 square feet. Forced draft will be by closed fire-room. The following are the dimensions of the machinery of the practice vessel: Cylinders 132, 21, and 31 inches in diameter, by 20 inches stroke. I. H. P. 1,300 at 240 revolutions per minute and 160 pounds working pressure. Piston-valves for H. P. and I. P. cylinders 6 inches in diameter. Crank-shaft journals and pins 6 inches diameter with 3-inch axial holes. Cranks at 120°, and sections of shaft interchangeable. |