ENGINEERING PROGRESS IN THE U. S. NAVY. 55 



At the effective horse-power value required for 2 1 knots by the Delaware, 

 the Utah requires 1.015 times as much fuel as the Delaware, a difference so 

 light as to be negligible. 



From the above results, it appears justifiable to decide as follows : — 



Should the duties of a vessel be such that she be required to steam for 

 long periods and long distances at speeds much lower than her designed maxi- 

 mum speed, a less fuel expenditure per day will be required, and consequently 

 a greater cruising radius will be obtained and less frequent recoaling neces- 

 sitated should reciprocating engines be fitted rather than turbines for pro- 

 pelling purposes. 



Should, however, the vessel operate from a fixed base, only doing suffi- 

 cient cruising to insure that the machinery is kept in efficient condition in 

 readiness for forced runs to any threatened point, the value of fuel economy 

 at low speeds becomes minimized and, where the maximum speed of the 

 vessel does not exceed 21 to 22 knots, either turbines or reciprocating engines 

 may be used, the choice being dependent upon other factors than economies, 

 which are practically equal at these speeds. 



In other words, for the conditions (b) and (c) , under which the American 

 battleship fleet operates, the reciprocating engine is preferable to the turbine 

 as a propelling engine at the present stage of turbine development. 



The Navy Department is, however, thoroughly alive to the advantages 

 to be gained by adopting rotary in place of reciprocating motion in the main 

 propelling machinery of the heavy vessels of the fleet, and, while recognizing 

 the present advantages held by the reciprocating engine in the matter of 

 economy at low fractions of designed power, holds itself ready to discard the 

 reciprocating engine as soon as the turbine designers can demonstrate by 

 actual performance that their claims as to equality of economy at low powers 

 with the older machine have been realized. It was with this object in view 

 that the department decided to install impulse turbines in the Nevada, and 

 not because the engineers of the department were "wobbling," as has been 

 charged. 



Condition (d) — Ease of Up-keep of Machinery. — The claim is frequently 

 made by the turbine advocates that while the reciprocating engine, when 

 new, is undoubtedly more economical than the turbine at small fractions of 

 designed power, this advantage is soon lost in active service, due to excessive 

 wear of piston and valve rings causing large losses through heavy leakage of 

 steam. The turbines, not being subject to such frictional wear, would, on 

 the other hand, retain their original economy indefinitely. 



Practical experience with both types of engine in actual service comes 

 very far from justifying this conclusion. In fact, with intelligent super- 



