14 REDUCTION GEARS FOR SHIP PROPULSION. 



place the machinery with turbines of much higher revolution. This necessitated, also, chang- 

 ing the gears, although they were quite satisfactory. This new machinery was fitted and 

 put into operation November, 1915, and has been in successful operation ever since, the ship 

 having sailed over 180,000' miles since November, 1915. 



The U. S. S. Wadsworth, built by the Bath Iron Works, Ltd., was the first destroyer of 

 the U. S. Navy to be fitted with reduction gears for the main drive. She was authorized 

 in March, 1913, and completed June, 1915. The machinery is twin screw and develops 

 16,000 shaft horse-power, that is, 8,000 shaft horse-power for each set and 4,000 shaft horse- 

 power per pinion. The turbines are compound, the high pressure on one side and the low 

 pressure on the other side of the large wheel, and the revolutions are : Propellers 450 revo- 

 lutions per minute, high-pressure turbine 2,494.5 revolutions per minute, and low-pres- 

 sure turbine 1,509.8 revolutions per minute. One peculiarity of this gear is that there is 

 only one helix. The steam thrust of the turbine acts against the propeller thrust and any 

 difference between the two is taken by a Kingsbury thrust bearing. This vessel was a remark- 

 able advance on any previous destroyer of the U. S. Navy, both as regards speed and effi- 

 ciency, and during the six years of service has operated in a very satisfactory manner. 



There are now about two hundred and fifty destroyers fitted with geared-turbine drives. 

 These are all single reductions of various makes and no trouble is being experienced with 

 them. 



The double reduction gear was introduced for the turbines of the battleship Nevada. 

 They were built by the General Electric Company and were distinctly novel. There is a single 

 high-speed turbine in each set and the pinion engages two wheels which in turn are coupled 

 to the two pinions of the second reduction and engage in the large driving wheel. The 

 shaft horse-power developed by each of these cruising sets is 1,750 and the speed reduction 

 23.35 to 1. These gears were tried out November 9, 1915, and proved very satisfactory, 

 the efficiency of the vessel from 10 to 15 knots being improved some 30 per cent at 10 knots 

 to 10 per cent at 15 knots. 



The same type of double reduction was further developed and fitted on the Pacific, built 

 by the Union Iron Works, and on the Sucrosa and Mielero, built by the Fore River Shipbuild- 

 ing Company. These sets were what is known as the "two-plane" type (Fig. 5, Plate 5), 

 the first stage or high-speed gear being comparatively small and carried above the center 

 of the main drive. This allows the latter to be as large as can conveniently be housed in 

 the ship and lends itself to sturdy, short second speed pinions. 



After making a few of the two plane gears, the single-plane type of double reduction 

 (Fig. 4, Plate 5) was introduced as a means of increasing production. The change led to a 

 rather cramped design as the low speed wheel has to be contained between the centers of the 

 high-speed train and cannot be increased without increasing the latter, and this limitation 

 led to a very considerable increase of tooth pressures. The units so designed are small and 

 showed a saving in weight and, as they performed well at the outset, the manufacture of this 

 type was generally adopted. 



We have now a variety of reduction gears in service and enough running has been 

 done to show that some types are good for continuous service and to point out some of the 

 defects in design, handling or manufacture. 



Lack of knowledge of gears and their requirements on the part of the engine-room 

 staff, improper lubrication, failure to keep the oil clean and free of water, especially salt 

 water, are some of the causes of wear and complicate the task of distinguishing between 



