64 ENGINEERING PROGRESS IN THE U. S. NAVY. 



To further illustrate the gains made by the short direct ports, attention 

 is called to Plate 33, where the back pressures on the low-pressure pistons of 

 several vessels at varying revolutions are shown as curves, the designed revo- 

 tions being marked on each curve by a circle. Of these vessels, the Delaware 

 is the only one with the modern type of port. 



In the last ten years, the cylinder ratio of low pressure to high pressure, 

 for triple expansion engines, has been increased from about 7 : i to 10 : i, 

 including clearances. This increase in ratio had been used previously in 

 remodeling the engines of the Cincinnati and Raleigh, with most excellent 

 results. A serious mistake was made, however, in counting too much on the 

 increased expansions obtained by fitting a smaller high-pressure cylinder than 

 that originally installed, the steam pressure having been increased. The 

 new high-pressure cylinder was made 24 inches in diameter and the ratio of 

 low-pressure to high-pressure cylinder changed to about 1 1^ to i . While the 

 economy obtained with these engines was most excellent, the high-pressure 

 cylinders were entirely too small and the engines have never developed the 

 expected power. 



By the adoption of forced lubrication for the main propelling engines, 

 the engine friction has been enormously reduced. All the journals are oil 

 born so that no metal to metal contact occurs. The result has been that the 

 amount of adjustment and overhaul of the main engines has been decreased 

 to a very large extent, and the men who would have been used for this over- 

 haul work can now be used on the auxiliary machinery to good advantage. 

 This decrease in wear of the bearings, and the cushion provided by the oil, 

 has resulted in a much better maintenance of alignment of the engines, has 

 reduced shocks on the machinery and has reduced vibration due to these 

 shocks. 



In addition, there is considerable saving in oil at ordinary speeds. At 

 high speeds there still exists a heavy loss of oil, due to splashing on the cyl- 

 inder heads and also to loss by evaporation from the hot surface of the lower 

 heads. 



When first fitted, the forced lubrication gave trouble, due to oil being 

 drawn through the low-pressure piston-rod stuffing boxes. In order to 

 remedy this defect, stuffing boxes fitted with steam seals have been supplied, 

 and later reports indicate that where the steam seal is properly fitted no 

 trouble of this kind now exists. 



That the foregoing changes have produced great economy is amply 

 demonstrated by the results obtained with the machinery installations of the 

 Michigan, South Carolina, and Delaware. Plate t,t, shows curves of indicated 

 horse-power per square feet of grate surface, and curves of square feet of 



