SUPERHEATED STEAM IN MARINE PRACTICE. 175 



and prevented the development of apparatus which could be cheaply constructed, 

 efficiently operated, and easily maintained at a minimum of cost. 



10. Another factor, which should not be overlooked, was that engineering 

 practice has been relatively crude in respect to the design of details which were 

 in contact with the steam. Cylinders, liners, valves, etc., were in many in- 

 stances of a quality of material which was not always entirely satisfactory even for 

 saturated steam. These conditions led to improvement of details, not so much 

 with the idea of adapting them to superheated steam as making them reliable 

 under saturated steam operation. Many details, thus improved in the past twenty 

 or twenty-five years, have been found entirely satisfactory for superheated steam. 

 Other details have required, with the widespread use of highly superheated steam, 

 still further improvement. It may be accepted that, at the present time in marine 

 practice, satisfactory service can be obtained from existing designs of details when 

 they are called upon to be in contact with superheated steam at temperatures up 

 to 625° F. 



11. The present tendency with regard to superheating is towards an increas- 

 ing amount. This is true not only in marine practice, but also in locomotive and 

 stationary engineering. It may be a matter of some surprise, to marine engineers 

 generally, to note what is actually being accomplished with the higher degrees 

 of superheat. The last decade has witnessed a wonderful advance in the adoption 

 of high degrees of superheat on locomotives. About 40,000 locomotives through- 

 out the world, of which more than 13,500 are in the United States and Canada, 

 are to-day operating with temperatures in the steam chest above 600° F. Some 

 roads in this country are using 700° temperature, while in France a large number 

 of engines are operating daily and with wonderful success, at temperatures be- 

 tween 750° and 800° F. Stop a moment to consider what these temperatures really 

 mean, especially in horizontal locomotive engines, as contrasted with the vertical 

 marine engine. The cylinders in a great many of these engines range up to 28 

 inches and 29 inches in diameter. They are horizontal engines, and run at piston 

 speeds considerably in excess of those used in ordinary marine practice. Many of 

 these locomotives operate at piston speeds of 1,500 feet per minute. That these lo- 

 comotives are not small engines is proven by the daily operation on several different 

 railroads in this country of engines in both passenger and freight service which 

 have shown above 3,000 indicated horse-power. We must not feel, therefore, that 

 the temperatures used on locomotives are in combination with small engines, for 

 the modern locomotive in the United States has practically the same indicated 

 horse-power as the average cargo-boat. In stationary practice the adoption of 

 superheat has been very rapid, and a large number of plants in the United States 

 are now in operation using at least 150° of superheat. In marine practice during 

 the last fifteen years, over 1,200 ships have been fitted with superheaters, all using 

 150° of superheat, and the majority of which are operating with practically 200° 

 of superheat. It is not exaggeration to state that, at the present time, well over 

 2,000 steamers are afloat using superheated steam, the majority of which are op- 



