54 ENGINEERING PROGRESS IN THE U. S. NAVY. 



CONDITION OP PLATE 2 CURVES. 



Curves A, B and C. — Actual trial conditions. 



Curve D. — Using same feed temperature conditions as for Curve C. 



Curve A . — Feed heaters not in use. 



Ctirve B. — Feed heaters in use. 



Curve C. — Feed heaters in use. Feed temperature much higher than A 

 and moderately higher than B. 



As practically the same amounts of heating medium for the feed heaters 

 were available in each case, it is justifiable to correct the British thermal 

 units absorbed by the boilers in A and B, by the amount of decrease due to 

 the higher feed temperature of C. 



Boilers in all cases were of the same type, but for A and B they were 

 fitted with superheaters. 



Boilers being of the same type they can be assumed of the same effi- 

 ciency, therefore the actual efficiency may be neglected and a boiler efficiency 

 of ICO per cent be used for comparison of performances without sensible error 

 in the comparison. 



Curve B is not exactly comparable with Curves A and C, as it does not 

 include full expenditures for all purposes as do the others, and hence it has 

 not been reduced to equal feed conditions with C. 



In preparing A, B, C and D, the following formula has been used: — 



Pounds coal per knot per hour = ^^ '^ 3 .1/^ — 



^ ^ 5X14500 ' 



where 



r= Total heat in steam at boiler pressure and superheater. 



/ — 32 =Feed temperature above 32° F. 



PF = Total water evaporated per hour. 



5 = Speed of ship in knots per hour for which W pounds of water are 

 evaporated. 



14,500 = Thermal value of one pound of coal. 



On this plate is also shown a curve of excess fuel for the Utah over 

 that required for the Delaware, all the curves being drawn with effective 

 horse-powers as abscissae. 



For the effective horse-power value required for 12 knots speed of the 

 Delaware, the Utah requires, by these curves, 22 per cent more fuel. From 

 the steam logs of the two vessels, the average excess fuel consumption of the 

 Utah over that of the Delaware at 12 knots is 20 per cent, thus corroborating 

 the results obtained from Plate 2. 



