The following text may have been generated by Optical Character Recognition, with varying degrees of accuracy. Reader beware!

MARINE REVIEKW. 15 rators are of the Davidson pattern; all the others are of Blake design ex- cept the air and circulatiug pumps on auxiliary condensers, which are Knowles. The screw propellers are of the modified Griffith design, true screw, three bladed, with adjustable pitch ranging from 19 feet 6 inches to 22 feet. The material is manganese bronze, and the diameter of the hubs is about one-third the diameter of the wheel. The center and starboard screws are right hand and the port screw is left hand. The center screw is 14 feet in diameter, while the wing ones are one foot greater, although the helicoidal area is kept about equal by widening the blades of the for- mer. Wing Screws. Senter Screw. Diameter of propeller, feet.........ccsscceceseceee 15 14 Diameter of hub, feet and inches............... 4-11% Pitch as set, feet and inches..................00- 22-0 21-6 Helicoidal area one propeller, square feet... 53-7 53 28 Disc area one propeller, square feet............. 176.7 153-9 Ratio pitch to diameter (as set)............0c0e0 1.46 to I 1.55 to 1 Immersion of upper edge of blade (normal draught), feet and inches 5-5 9-I have but two furnaces each. All the furnaces are of corrugated steel. The main boiler shells are in three lapped courses, with three sheets in each course, butted, and strapped inside and out. There is one quadruple safety valve (each valve four inches in diam- eter), on each main boiler, and these, as well as the stop valves, can be operatnd from the berth deck. All the material is mild steel, including the tubes. The latter were rolled by the Reading Iron Co. from open- hearth steel especially made for the purpose by the Pottstown Iron Co., and are most excellent in finish and quality. Data for one boiler follows: Shell, length, 20 feet; diameter, 15 feet g inches; thickness, 1}; inches; number courses, 3; sheets in course, 3; furnaces, number, 8; diameter (least inside), 4o inches; diameter (greatest inside), 42% treneet thickness, ;°; inches; length of grates, 84 inches; number of grate hare each furnace, 7; tubes, number of ordinary No, 12, B. W. G., 948; tube heating surface, square feet, 5,539.89. Totals for main boilers are: Heating surface, 48,104.54 square feet; grate surface, 1,456.2 square feet; area through tubes, 209.8 square feet ; volume steam space, 6,806.6; area water surface, 2,060.6 square feet; net ~ area two main smoke pipes, 196 square feet; aggregate length (exposed) of all tubes, 12.7 miles. SS ae Sh ee area ee rcep TANK a a 4 > | __-- MAIN DENSER "Ei oxa| FRO AOILGE ° sine WOILEK eure o ° FELO TANNA AIR PuMP MAIN insects 1ON bean § THE THREE ENGINE ROOMS Each blade weighs about 3,900 pounds, or 11,700 pounds for the blades of each screw, and each hub about 7,200 pounds. making nearly 19,000 pounds for each propeller complete. There are eight main and two auxiliary cylindrical boilers. The six after main boilers are the largest of modern marine types, being 15 feet 9 inches in diameter and 20 feet long--two feet longer than the largest boilers in the Columbia, though of the same diameter. The other boilers are sim- ilar to the Columbia's, but by reason of the increased size of the above six the total heating surface of the main boilers is 48,194.54 square feet, and the total grate surface 1,456,2 square feet, against 43,268.13 and 1,344 square feet respectively for the Columbia. This greater boiler power is the only important difference in the machinery of the two ships. Each of these larger main boilers weighs about 72 tons empty and without fittings, and contains about 4o tons of water at steaming level. All the main boilers have flat ends, but the auxiliary boilers have the ends curved back at the top toa radius of 2 feet 2% inches. The latter boilers are in separate open fire rooms on the protective deck. The Cone patent rocking grate is used in all thefurnaces. The main boilers are double ended with four furnaces ateach end. The two adjacent furnaces on each side of each end have a common combustion chamber. The auxiliary boilers are single ended and = : ee alee a ALN STEAM AUS EXHAUST AVA, STEAM AUK. CONDENSER Avr. CONDENSER AUK, STEAM. AVA Ext AUST AN Convensen © FILTER C€tiveny our FECD Tann OF THE MINNEAPOLIS. Sixteen 60-inch Sturtevant blowers are used for forced draft, two blow- ers being placed in front of each end of each main boiler overhead, draw- ing air through air ducts from above decks, and -each blower having a capacity of 10,200 cubic feet of air per minute, with an air pressure of one inch of water in the fire rooms. . The electric plant of the Minneapolis consists of three 24 'kil- lowatt direct connected generating sets, having the generators di- rectly connected to a double cylinder simple vertical engine. The capacity of each generator is 300 amperes at 80 volts. These sets are built by the General Electric Company especially for marine ser- vice, and, of course, are constructed to meet requirements of the gov- ernment specifications. The controliing and measuring instrumcnts are mounted on a navy standard slate switchboard placed near the genera- tors. Every appliance is of standard type. The porcelain used is man- ufactnred at the General Electric Company's own porcelain factory, and is of the hard white vitrified variety which has been found to satisfy the government insulation requirements as no other has heretofore done. The vessel is lighted by 500 incandescent lights placed in regular gov- ernment standard fixtures. In addition there are two search lights one having a reflector twenty-four inches in diameter, the other with athirty-