214 THE SUBMARINE OF TO-DAY AND TO-MORROW. 



dominating over the four-cycle, although many of the German boats are equipped 

 with four-cycle engines constructed by the Augsburg Works, the others being 

 equipped with two-cycle engines constructed by the Krupp and Nuremberg Works. 

 In France and Russia, both two and four-cycle engines are employed and there is a 

 tendency towards the use of engines of greater weight and more moderate speed. In 

 England, the two-cycle engine has not found favor. Practically all of the English 

 boats are equipped with four-cycle engines of moderate speed and weight. No effort 

 appears to have been made to gain a slight increase in surface speed by the use of 

 the lightest possible engines. In the United States, both two and four-cycle en- 

 gines have been installed and in a number of cases the two-cycle engines have been of 

 the high-speed, light-weight type. The tendency now is towards the use of a heavier 

 engine of more moderate speed, a development which means an increase in the dis- 

 placement of the boats in order to avoid a loss of surface or submerged speed. 



The lightest Diesel engines so far employed weigh about 50 pounds per brake 

 horse-power and operate at a speed of about 500 revolutions per minute. The 

 heaviest engines weigh about 100 pounds per horse-power and operate at a speed of 

 about 350 revolutions per minute. A fair average for single-acting engines of sub- 

 stantial construction and moderate speed may be taken as 70 pounds per horse- 

 power. While future development will no doubt result in some decrease in weight 

 without sacrificing durability or reliability, there is no reason to believe that the 

 improvement in single-acting engines will be radical. Internal-combustion engines 

 in general, however, have not yet by any means reached the limit of their develop- 

 ment, and it is not unreasonable to assume that it will be possible to produce units 

 of this type of great power of substantially the same weight and space as that re- 

 quired for steam installation and comparing favorably with the latter with respect 

 to the matter of reliability. 



In the present stage of development of the single-acting Diesel engine, it is en- 

 tirely practicable to install a submarine power plant of from four to five thousand 

 horse-power in a boat of from 900 to 1,100 tons surface displacement. When this 

 displacement is coupled with a length of about 260 feet, a speed of from 20 to 21 

 knots can be obtained with the above power. When we come to consider the ques- 

 tion of a speed of 25 knots or more, it is well to remember that excessive length in 

 a submarine is in itself a very undesirable feature. In operating submerged, it is 

 not always possible to avoid some fore and aft inclination of the boat's axis, and, 

 when great lengths are involved, comparatively small angles of inclination result in 

 great diflferences in the level of the bow and stern. Obviously, then, the greater the 

 length, the greater the depth of water required for rapid and safe submerged ma- 

 neuvers. On this account, having in view the possible and probable uses of the 

 fleet submarine, every effort will no doubt be made to keep the length within reason- 

 able limits. Adopting say 300 feet as the limit of length and coupling this with a dis- 

 placement of about 1,200 tons on the surface, from ten to twelve thousand horse- 

 power would be required for a surface speed of 25 knots. An installation of Diesel 

 engines of such power would at this writing be experimental. It follows that, not- 



