148 ELECTRIC PROPULSION OF SHIPS. 



Table of Detail Weights for a 3,000 S. H. P., 90 R. P. M. Drive. 



Item 



Double 



reduction 



geared 



turbine 



Turbine 

 electric 



Direct Diesel 

 (twin screw) 



Diesel 

 electric 



Prime mover 



Boilers and superheaters 



Condensers and auxiliaries 



Water in machinery 



Reserve water for machinery 



Propeller shafting 



Propeller shaft bearings 



Gratings, ladders, etc 



Control and cable 



Steam and water piping 



Independent auxiliaries 



Uptakes, air box, stack, etc 



Totals 



Lbs. per S. H. P. total machinery . 

 Ratio, geared turbine, unity 



*100, 000 



t360, 500 



50, 000 



200, 000 



250, 000 



115, 000 



15, 000 



60, 000 



100, 000 

 32, 000 

 70, 000 



*206, 000 



t360, 500 



50, 000 



200, 000 



250, 000 



115, 000 



?30, 000 



60, 000 



18, 000 



100, 000 



82, 000 



70, 000 



*1, 200, 000 

 Jll, 200 



*1, 060, 000 

 til, 200 



45, 000 



45, 000 



135, 000 



?45, 000 



50, 000 



32, 000 



130, 000 



11, 000 



115, 000 



S30, 000 



50, 000 



II 

 32, 000 

 20, 000 

 14, 000 



1, 352, 500 

 451 

 1 



1, 491, 500 

 497.5 

 1.103 



1, 659, 200 

 552.5 

 1.227 



1, 368, 200 

 452.5 

 1.003 



NoTE^Using watertube boilers, the two turbine drives would be reduced about 250,000 pounds. However, the 

 installations using such boilers are relatively very few in comparison with those using Scotch boilers. 



* 180 R. P. M. engines with exciters. t Scotch boilers. t Vertical boilers. 



§ Include thrust bearing. H Included in prime mover. 



conservatism of such an engine. This engine is available today in sizes suitable for elec- 

 tric drive. 



Another absolutely reliable Diesel engine for electric drive is available, weighing 180 

 pounds per brake horse-power for the engine alone and operating at 250 R. P. M. The com- 

 plete Diesel electric drive using this engine instead of the one used in the table is 402 pounds 

 per shaft horse-power, and the ratio of this weight to the weight of the geared turbine drive 

 is 0.892. 



Developments will undoubtedly be undertaken by some present Diesel engine manufac- 

 turers to commercially produce a lighter Diesel engine which will be suitable for electric- 

 drive units. The ultimate outcome of this development should produce a conservative engine 

 weighing not more than 125 pounds per shaft horse-power and operating at 300 R. P. M. 

 Using these engines instead of those in the table, the weight of the complete Diesel electric 

 drive would be 328 pounds per shaft horse-power, and the ratio of this figure to that for the 

 geared turbine is 0.727. 



The weight of 400 pounds per brake horse-power for the direct-drive Diesel used in the 

 table is lower than the average engine actually installed and operating today, which, accord- 

 ing to authoritative data, is 483 pounds per brake horse-power. On the 483-pound basis, 

 the weight per shaft horse-power for a complete direct Diesel drive is 635 pounds, and the 

 ratio of this figure to that for the geared turbine is 1.41. 



