66 ENGINEERING PROGRESS IN THE U. S. NAVY. 



The improvements in design of feed heaters, steam pipes and feed pipes 

 naturally followed on the measurements of water consumptions of the 

 machinery taken during the acceptance trials of the vessels. These measure- 

 ments placed in the hands of the Bureau of Steam Engineering data of great 

 value, and that bureau has attempted to use the full value of it in propor- 

 tioning these important items. 



For instance, the feed heaters of the Delaware were, for lack of data, 

 proportioned on the basis of so many indicated horse-power per square foot 

 of heating surface, and the two heaters combined have a total heating surface 

 of 2,100 square feet. In her sister ship, the Utah, the same degree of feed 

 heating is obtained with heaters having a total surface of only 512 square 

 feet. 



In the search for economy, the Bureau of Steam Engineering has adhered 

 strenuously to the use of feed heaters with auxiliary exhaust steam as the heat- 

 ing medium, using any excess of exhaust in the low-pressure turbines or the 

 second receivers of triple expansion reciprocating engines. This utilization 

 of the auxiliary exhaust has not been to the taste of the turbine manufacturers 

 who prefer to use all of this steam in the turbines, depending for feed heat 

 upon that derived from steam drains discharging into the feed tanks. 



That the bureau's contention that greater economy of fuel is obtained 

 by the utilization of the auxiliary exhaust in the feed heaters is correct 

 is shown by the curves given on Plate 33. The boilers of the vessels from 

 which these results were obtained were so similar that the efficiencies may 

 be taken equal, and the comparison can then be made on an assumption 

 of 100 per cent efficiency without much error. The fuel oil per knot is 

 obtained from the heat units per knot absorbed by the boilers for the different 

 speeds, and dividing these different heat unit values by an assumed British 

 thermal unit value per pound of fuel. At 29 knots it will be seen that the 

 vessel making full use of her feed heaters required only 84.2 per cent as much 

 fuel as the vessel putting all the auxiliary exhaust into the turbines (closed 

 exhaust), and only 92 per cent as much as the vessel using the feed heaters to 

 a limited extent. 



The same comparison is shown on Plate 34, where are also shown the 

 shaft horse-power curves for two vessels of similar hull but one being fitted 

 with two shafts and the other with three. Here at 29 knots, the three-shaft 

 vessel, though having a poorer propulsive coefficient than the two-shaft one, 

 only requires 90.4 per cent as much fuel per knot. The shaft horse-power of 

 the two shaft vessel is only 98.44 per cent of that for the three-shaft one. 

 Had they been equal the fuel for the three-shaft arrangement would have 

 been still lower as compared with the other vessel. 



