ENGINEERING PROGRESS IN THE U. S. NAVY. 67 



The improvements in evaporators consist mainly in the adoption of 

 double efifect connecting and in throwing open the gates to other than the 

 standard bureau design, although these are not the only changes from former 

 practice. Evaporator feed heaters, using the vapor from the evaporators as 

 a heating medium, have been fitted, and vapor pipes better designed for the 

 amount they have to carry are installed. 



Until the adoption of electric-driven blowers for battleships and other 

 large vessels and of turbine-driven blowers for destroyers and small vessels, 

 the successful outcome of any heavy forced-draft run was always endangered 

 by the unreliability of the blowers. Since the adoption of these types of 

 blowers this danger of breakdown has been almost entirely eliminated, and, 

 so far as the destroyers are concerned, the blowers may be classed as one of 

 the most, if not the most, reliable of the auxiliaries fitted. 



OIL FUEL FOR DESTROYERS AND BATTLESHIPS. 



In deciding to adopt oil fuel for use on battleships and destroyers, the 

 Navy Department took into account the following advantages which would 

 be gained by its adoption : — 



1. Less fuel required for any given radius of action, consequently less 

 percentage of displacement and less bunker capacity required for the fuel. 



2. Increased boiler efficiencies. 



3. Decreased fire-room force. 



4. Less deterioration of boilers due to maintenance of more even 

 temperatures. 



5. Ability to maintain high powers for indefinite periods. 



6. Less deterioration of ship's structure due to there being no water or 

 ashes in the bilges. 



7. Greater cleanliness. 



8. Greater ease in replenishing fuel supply, both in port and at sea. 



9. Less floor space required for the development of a given power. 



10. Greater ease in control of steam supply. 



In opposition to these undoubted advantages the following disadvan- 

 tages exist : — 



1. Fuel oil less widely distributed over the earth than coal. 



2. Greater unit cost than coal. 



3. Greater danger of fire than with coal. 



The reply to the first disadvantage is that in time of war a fleet operating 

 far from a base would depend upon fuel ships for replenishing her bunkers, 

 and that oil can be carried in bulk as well as coal, and bases where stores of 



