ELECTRIC PROPULSION OF SHIPS. 129 



what differently, but the foregoing indicates substantially the condition in the arrangements 

 described. 



It is quite apparent that the comparative advantages of Diesel propelling machinery or 

 Diesel electric machinery are considerably less in installations for oil tankers, owing to the 

 large amount of steam required for heating heavy oils during the voyage and when 

 discharging. 



There are many other vital points brought out in Mr. Thau's paper upon which I have 

 not had time to prepare a discussion. 



I consider that the Society is fortunate in being able to incorporate in its proceedings 

 the valuable paper presented by Mr. Thau. 



Mr. William W. Smith, Member: — Mr. President and gentlemen, on page 108 the 

 author states that economically a geared turbine drive is generally more efficient than an elec- 

 tric drive. I have also found this to be true, the saving in steam consumption in favor of 

 the geared-turbine machinery being from 4 to 8 per cent. This feature is of especial import- 

 ance, because statements to the contrary have been made frequently. 



It is also pointed out on this page that geared turbine machinery can use high degree 

 superheat. This is also a fact. Some fairly large passenger steamers with geared turbine 

 machinery using 200 degrees superheat have recently been put in service by the Cunard and 

 other leading British steamship lines. It is important to point out here, also, that misleading 

 statements as to the inability of geared turbines to use high degree superheat have frequently 

 been made. 



We have made a number of designs for different types of machinery, but have not found 

 the differences in space referred to by the author. We have found that all of the types re- 

 ferred to occupy about the same space except the turbine-electric machinery, which requires 

 more space, and especially when the motor is located aft. I might add that where the motor 

 is located aft, I do not think it is permissible to eliminate the shaft alley. I do not quite 

 agree with some other gentlemen in this respect. I think it is essential for the engineer to be 

 able to visit the motor room easily and frequently without having to go up on deck and 

 make an excursion such as I had to make on an electric ship not long ago. 



The author refers to the saving effected by eliminating the boilers, but neglects to say 

 that Diesel machinery is far larger and heavier than the remaining machinery. The pic- 

 ture of eliminating boilers, and pointing out the rest of the machinery as comparable with 

 Diesel engines as to weight, space and cost, is often described. This, however, is far from 

 the facts, since the Diesel engine installations occupy about the same space, and weigh nearly 

 twice as much as a complete steam installation including boilers. 



On page 109, the author's statement as to the cost of the various types of installations 

 is at variance with my experience. I have found the cost per shaft horse-power of complete 

 machinery installations of cargo vessels of ordinary size to be relatively about as follows: 



1. Geared turbine vessels — 50 degrees superheat $122 



2. Steam engines — saturated steam 132 



3. Diesel engine — direct drive, twin screw 240 



4. Diesel engine — electric drive, twin screw 260 



Variations in designs and conditions would modify these figures somewhat. This would 

 apply to modifying item 4 to single screw. As the size of vessel decreases, the direct-drive 

 Diesel installation works out to better advantage. 



