62 ENGINEERING PROGRESS IN THE U. S. NAVY. 



15. Improved evaporators and other auxiliaries. 



In addition to the above, the reUabiUty of the machinery plant has been 

 improved by — 



16. Adoption of high-speed, electric-driven forced-draft fans for battle- 

 ships. 



17. Turbine-driven forced-draft fans for destroyers, and the most 

 important of all — 



18. The adoption of oil fuel for both battleships and destroyers. 

 Considering the above changes in detail, the steam pressures at the main 



engines since 1895 have been increased gradually from 150 pounds per gage 

 to 265 pounds per gage in the high-pressure valve chest, resulting in decreased 

 size of engine cylinders and in decreased size of steam piping for equal units 

 of power. 



The engine framing of the vertical engines first fitted was either of cast 

 steel or built up of steel plates, as shown on Plate 37. On several vessels 

 trouble has been experienced with this type of framing, particularly when 

 made of cast steel, and, in addition, the weight was high. The Bureau of 

 Steam Engineering, in order to overcome these faults, designed and adopted 

 the style of framing shown on Plate 38 for the Kearsarge and Kentucky, and 

 this style of forged steel, built-up framing has been adhered to. 



Since the adoption of this type of framing, framing troubles are unknown 

 notwithstanding the fact that the weight of the modern framing per indicated 

 horse-power has been reduced to about 3.3 pounds against 5^ pounds for the 

 old. 



Since the design of engines for the Oregon were laid down, there has 

 been a gradual increase in piston speeds used, from 900 feet in that class to 

 1,000 feet in the Delaware class. This increase in piston speed has been fol- 

 lowed by decrease in weight of the moving parts and has aided in holding 

 down the weight and height of the engine, although the stroke has been 

 increased from 42 inches to 48 inches. 



On Plate 36 are shown lines giving the maximum and minimum 

 heights of naval engines for dififerent lengths of stroke, also the line of cross- 

 head pin centers and crank-pin centers. These curves are all for engines 

 having the bureau's standard ratio of four to one between the connecting- 

 rod length and crank-pin arm. 



In the use of superheated steam, the Bureau of Steam Engineering has 

 been rather conservative ; at present there are seven vessels in the naval ser- 

 vice fitted for superheat, the maximum degree of superheat obtained at the 

 boilers being 85° F. which reduces to about 60° F. at the engines. These 

 figures are for full-power conditions, and an increase in economy of about 



