20 REDUCTION GEARS FOR SHIP PROPULSION. 



ameter by 48-inch stroke, two cycle. In this ship all the main and auxiliary deck machinery 

 is driven electrically. 



The electric drive consists of one turbo-generator w^ith an auxiliary g-enerator to give 

 a speed of about six knots, and two large motors, one on each propeller shaft. The boilers 

 are the same as for the turbine drive. 



This comparison was not made out to favor any particular engine and is probably a 

 fair representation of the relative weight, space and costs of the different types of machinery 

 for these vessels. With the cheap rate for oil which it is possible to secure on the particular 

 service for which the vessels are designed it is found that the turbine machinery makes the 

 most attractive proposition, but as regards the mere cost of operation this advantage would 

 swing to the Diesel engine with an increased cost of fuel, that is, providing the Diesel en- 

 gine would operate satisfactorily on the same low grade of oil as is contemplated for firing the 

 boilers. 



It is considered that the turbine installation is the simplest to operate and will entail far 

 less repair at the end of each voyage, so that the turn around can be made in quicker time, and 

 that is of the greatest importance when special arrangements are made for loading and un- 

 loading, so that the time for this is counted in hours and not days. The turbine set has the 

 further advantage of great flexibility and can be driven up to 15 per cent over normal full 

 power when required. 



It is interesting to note that the cost of the turbine installation is somewhat less than 

 that of the reciprocating machinery, and if the boilers had been reduced to the extent war- 

 ranted by the decreased steam consumption of the turbine there would have been a still fur- 

 ther reduction in weight and cost. It was, however, considered to be an advantage to have 

 the boilers operating under easier conditions for the normal full power and to have available, 

 when required, the extra power and speed. 



The arrangement of the turbine and gears is shown on Plate 6. 



When comparing the efficiency of turbines and reciprocating engines it is usual to con- 

 sider the best steam consumption of both. The turbine having good clearances and no wear on 

 the parts affecting economy should maintain its efficiency, but the reciprocating engine falls 

 off rapidly, due to the wear on valves and piston rings, liners and cylinders. 



The question of gear efficiency has been much debated and various factors have been 

 given from time to time. The Falk Company devised a means of testing them under full 

 load, for bearings and teeth, with a motor large enough to supply the amount lost in friction 

 only. This was further extended so that they could be tested for efficiency and tests were 

 subsequently made on a number of gears, the results of which the Falk Company have kindly 

 allowed me to add to this paper. 



The first of these was on two sets of single reduction gears for one of the 35- 

 knot destroyers built by the Bethlehem Shipbuilding Corporation at Fore River. The method 

 is shown on Plate 7. The two gears, port and starboard, are placed back to back with a 

 space of 10 or 12 feet between them. The main shafts and pinions are coupled together, 

 the latter by means of torsion shafts with large coupHngs so that the twist on the shaft 

 can be varied at will. By this means it is possible to put the same load on the bearings 

 and to run the gears at the same tooth pressures and imder the same conditions as when 

 operating on board ship. The two sets are driven by a D. C. motor at the required speed 

 and the power developed by the motor represents the friction of all the gears and bearings 



