118 ELECTRIC PROPULSION OP SHIPS. 



The Diesel electric has the greatest range of application of any of the economical 

 drives (geared turbine and turbine electric not excepted). Because of the inherent merits 

 of this drive, it is very suitably applied to merchant ships, barges, river boats, lake boats, 

 ferry boats, small coastwise vessels, yachts, fishing boats, coastguard cutters, cable-laying 

 ships, and any ship within its capacity requiring refined control and economical operation 

 over a wide range of speed. 



As compared with any type of steam drive, the principal advantages of the Diesel elec- 

 tric are: Fuel consumption; weight; control; considerably more reserve power in case of 

 casualty to prime movers. 



The principal advantages of the Diesel electric drive as compared with direct Diesel 

 drive are: 



Reliability. — Cylinder parts being thinner are not subjected to such high temperature 

 strains in heads and liners as are the large slow-speed engines, and consequently there will 

 be fewer breakages of these parts. Years of application and service demonstrate beyond a 

 doubt the full reliability of electrical machinery. 



Maneuvering Ability and Control. — The control is extremely simple, easily understood, 

 and can be placed anywhere on the ship. The engines nui at constant speed, and hence the 

 engine reversing gear is eliminated. . 



Weight. — On a very conservative basis, the Diesel electric should show at least 100 

 pounds less per propeller shaft horse-power. 



Propeller Application. — Propeller speed not restricted, and in the case of large ships one 

 propeller would be used for Diesel electric, whereas, because of engine conditions, two would 

 be used with direct Diesel. 



Reserve Power in Case of Casualty. — Very much greater with Diesel electric. 



Maintenance. — For reasons under "Reliability," the maintenance should be less. Fur- 

 thermore, due to smaller parts and reserve power, repairs to Diesel electric engines can 

 usually be made on board ship while under way, providing sea conditions permit. The en- 

 gines for Diesel electric are designed and built on the same conservative basis as direct-drive 

 Diesels and are not the high-speed, short-lived submarine type. 



Less Starting Air. — Diesel electric requires starting air only during the initial start in 

 port. Subsequent engines may be started electrically. No air is used during reversing, and 

 consequently the air problem is reduced to simplest terms. 



Fuel Consumption. — There would be little difference in the net fuel oil and lubricating 

 oil consumption as the increased efficiency of screw and the reduced strutt losses, with the 

 low-speed single-propeller Diesel electric, offset the twin-screw arrangement of the direct 

 Diesel. From a standpoint of piston speed, the engines used for Diesel electric drive are no 

 different than direct-connected engines. (The former exceeds the latter only in revolutions 

 per minute.') 



Cost. — ^The cost of Diesel electric in some cases is less than the cost of direct-connected 

 Diesel drive on present-day figures and will generally ^ow a greater gap when fully de- 

 veloped along standardized lines. 



GENERAL SUMMARY FOR MERCHANT-SHIP ELECTRIC DRIVES. 



In the way of a summary relative to all types of electric propulsive equipments for mer- 

 chant ships, the following salient features may be reviewed: 



1. Electric drive is as reliable as any drive suitable for ship propulsion. 



