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ACR-10 Tennessee / CA-10 Memphis - Propelling Machinery

The propelling engines were of the vertical, twin screw, four-cylinder, triple-expansion type, of a combined I. H. P. of 23,000. The steam pressure was 250 pounds, and the stroke four feet. A speed of the main engines of 120 revolutions per minute was requisite to a speed of 22 knots. The diameters of the high pressure and low pressure cylinders were in the ratio of i to 7.3. The engines were located in two separate watertight compartments. Steam, at a working pressure of 250 pounds, was supplied by sixteen boilers of the straight water-tube type, placed in eight water-tight compartments, having combined grate surface of at least 1590 square feet, and heating surface of at least 68,000 square feet.

Forced draft was on the closed fire-room system. There were four funnels on each vessel, each about 100 feet high above the keel line. The firerooms of the Tennessee consisted of eight symmetrically arranged compartments with forced draft on the closed fireroom system. Each compartment is capable of being converted into an air-tight space. The air is forced in by fans 5 feet in diameter making 500 revolutions per minute, raising the inside atmospheric pressure about 1 to 2 inches (water manometer), and by this compression of the air the temperature is slightly elevated (5 for every inch of pressure). Three times the usual amount of coal is consumed in forced draft, necessitating nearly treble the amount of work for the firemen.

The stokers stand directly under the blowers, with air of 116 to 140 F. and 8 to 50 per cent R.H., and velocity of 3,000 to 4,000 feet per minute blowing over their sweating bodies. Every one to three minutes they open the furnace doors and expose themselves, for a few seconds while stoking, to a temperature of 166 to 179 F., and then again assume a position of rest under the blowers. This muscular labor and change of temperature every few minutes causes free perspiration, which is rapidly evaporated by the powerful blast of hot, dry air, thus producing an extremely artificial condition seldom simulated by nature. Notwithstanding this high temperature it is by no means unpleasant under the blowers, as thermolysis seems equally increased as therniogenesis, hence causing thermotaxis to remain normal.

But above the blowers we have a different meteorological condition; this has been termed the area of "superheated air." The warm air rises, accumulates there, and can find no exit, thereby causing an air temperature of 170 to 195 F. with no appreciable drafts to ameliorate the heat. Oilers and others worked there 10 to 15 minutes at a time. The temperature was so high that, in repairing one of the blowers, it was necessary to keep the implements in cold water to permit use by bare hands.

Feed water was carried in the double bottoms. The vessels were heated by steam throughout. There was a refrigerating plant of the Dense Air type, with a cooling effect equal to a daily output of three tons of ice. There was an evaporating plant of not less than four units, having a total capacity of 25,000 gallons of potable water per day, and a distilling apparatus capable of distilling at least 10,000 gallons of water per day.

Special attention was given to the coaling of these vessels. It was the intention to hoist the coal over all, and to lower it directly through large hatches to the gun deck, where it can be handled on trucks to the various scuttles, thus avoiding the fitting of a large number of scuttles on the gun and main decks, and the fitting of portable coal chutes.

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Page last modified: 22-07-2011 17:36:12 ZULU