DISCUSSION ON MAY MEETING PAPERS. 51 



Mr. Katzenstein, representing the Worthington Company, has advocated and defended 

 the proposed Diesel-electric drive on the ground that the higher-speed trunk-type engine has 

 been satisfactory as auxiliary engines on B. & W. vessels. It should be noted that the func- 

 tion of auxiliary engines and their operation is entirely different from the main engines as 

 they are very seldom operated at full power, and then only for a specified time, when each in 

 turn is shut down and another started up in its place. It might be stated in this connection 

 that there is a strong tendency at present, on the Continent in particular, to replace the 

 larger sizes of trunk-type engine for land purposes by the crosshead type, due to the generally 

 recognized superiority of the latter, although the weight and cost are higher. For the main 

 drive in a motor ship it cannot be too strongly emphasized "that the best is none too good" 

 for reliability and continuity of operation, which are of the utmost importance. Mr. Katzen- 

 stein has also referred to their land engine of the horizontal type, commonly used for driv- 

 ing pumps of oil lines, which are known to be quite heavy and not permissible in a Diesel- 

 electric drive, where the high-speed light-weight engine is a requisite to keeping the total 

 weight of machinery and the space occupied within reasonable bounds. 



Mr. Anderson, representing the Parsons Company, states that the motor ship cannot make 

 as good an average speed in bad weather as the steamer, when, as a matter of fact, the 

 motor ship has a considerable advantage in this respect. The larger diameter single screw 

 employed with the steamer has a tendency in bad weather to be longer out of the water than 

 the smaller diameter twin screws of much greater immersion in the motor ship, and it is 

 apparently only when the screws are in the water that the power can be effectually applied 

 to driving the vessel. Furthermore, there is no throttling of the power in the Diesel engine, 

 as with the turbines for the steamer, in rough weather. This is accounted for in the oil 

 engine being able to have all the power instantly cut ofif when the revolutions exceed a cer- 

 tain determined value, reached when the screws are out of water, and is instantly cut in 

 again when the screws are returned to the water. The average all-year propulsive efficiency 

 will also be better for the twin screws as a result of their better immersion under all condi- 

 tions of draught. Mr. Anderson considers the oil per shaft horse-power of 0.95 pound, all 

 purposes, for the geared turbine, as used by the authors, can be improved on some 10 per 

 cent with 150 degrees superheat. We are, however, dealing with operating conditions, and 

 higher economy implies a very good vacuum for the turbines, and it is a known fact that 

 it is chiefly due to not realizing the designed high vacuum in actual service that accounts for 

 the discrepancies between trial data and actual performance of turbine vessels. This is 

 particularly noticeable when the vessels are run over tropical routes. The efHciency of the 

 steamer also has a tendency to fall off in service as the boiler heating surfaces deteriorate. 

 The above conditions do not affect the Diesel engine, which actually improves in economy 

 and which in no way is affected adversely by tropical conditions. Mr. Anderson questions 

 the 0.31 pound per indicated horse-power for main engines, all purposes, used by the authors, 

 and has referred to figures published in Engineering of February 15, 1915, which give a 

 mean of about one-third of a pound of oil per indicated horse-power for B. & W. installa- 

 tions up to that date. The explanation for this is that the consumption then published repre- 

 sented the earlier design of B. & W. engines, in which the compressor for the injection air 

 had its first two stages driven by separate auxiliary engines, which is a less efficient arrange- 

 ment than now used, where a three-stage compressor is driven by the main engines alone. 

 Some development in the art is to be expected in that time contributing towards improved 

 economy, as likewise noted in the steam turbine. 



