190 THE APPLICABILITY OF ELECTRICAL PROPULSION TO 



this slightly increases the turning circle, but does not increase the space necessary 

 to turn in, as the inboard screw can always be stopped or backed. 



Before taking up the work of the Jupiter's engines, a brief description will 

 be given of the ship and her propelling machinery. The Jupiter is of the twin- 

 screw, single-deck type. She was designed for a speed of 14 knots, developing 5,500 

 shaft horse-power, with a load displacement of 19,300 tons, at a draught of 27 feet 

 8}4 inches. The general dimensions of the ship are as follows : — 



Length over all 542 ft. 2^ ins. 



Beam, extreme 65 ft. 3 ins. 



Draught, mean designed 27 ft. 85^ ins. 



Coefficient of fineness, block 7215 



There are three double-ended, retiirn-tubular, marine type Scotch boilers, and 

 one upright donkey boiler. The main boilers have the following dimensions : — 



Length over all 23 ft. % in. 



Diameter 16 ft. 3 ins. 



Diameter of furnace (inside) 3 ft. 4 ins. 



Number of furnaces, per boiler 8 



Length of grates 5 ft. 7^ ins. 



Grate surface per boiler 150 sq. ft. 



Heating surface per boiler 6,460 sq. ft. 



These boilers are designed for a working pressure of 190 pounds per square 

 inch, but safety valves were set for 200 pounds per square inch for the preliminary 

 trial. Howden's forced draught system is used. The incoming air to the blowers, 

 which are of the Sturtevant type, passes through the motors and generator, thus 

 giving a certain amount of preheating to the air which is used for combustion. 



There are two solid, manganese-bronze propellers. They have a taper fit on 

 the tail shaft, and they are keyed and held in place by a bronze nut. They have the 

 following dimensions : — 



Diameter 15 ft. 1 1/^ ins. 



Pitch 14 ft. S^ i^s. 



Expanded area 70.5 sq. ft. 



Projected area 60.53 sq. ft. 



Disc area 198-97 sq. ft. 



Weight, one propeller 13,900 lbs. 



These propellers were designed by Captain C. W. Dyson, U. S. Navy, and show a 

 remarkable efficiency, giving the same speed as her sister ships on from 300 to 800 

 less horse-power. 



