ELECTRIC PROPULSION OF MERCHANT SHIPS. 287 



Concerning- the electrical installation, Mr. Emmet gives figures with some degree of 

 looseness. He refers to the space to be saved by eliminating the shaft alley and says that 

 the space occupied by the shaft alley amounts to 12,000 cubic feet, or 3 per cent of the total 

 capacity of the ship; 5 by 7 feet would be a great sufficiency for the tunnel area, and its 

 length, 143 feet, gives 5,000 cubic feet capacity against Mr. Emmet's 12,000. As the dis- 

 cussion pointed out, the geared turbine installation may be placed aft as in, the case of 

 tankers, if desired, which would make reference to the space occupied by the shaft alley 

 as irrelevant. 



Mr. Emmet discusses the reversing elements of turbines, but I do not think he knows, 

 and I am sure I do not know of a single instance where a vessel has got in trouble because 

 of the heat generated in the ahead elements while the turbine is running astern. I know 

 of one instance where, on the return from a trial trip, a vessel was stuck on a mud bank and 

 ran full speed astern the whole night with no trouble resulting. Mr. Emmet submits a curve 

 which we understand to show the temperatures resulting from running the turbine full 

 speed in the astern direction, and admitting first 7.6 per cent of full load steam through 

 the ahead elements and then 13.2 per cent of full load steam through the ahead elements, 

 the vacuum in the exhaust being 28.9 inches. The above is rather suppositious, for the 

 text is not entirely clear as to these conditions of operation. If my assumption is correct, 

 we can see no relevance in the matter, for no sane person would purposely admit any quan- 

 tity of steami through the ahead elements while the turbine is running astern. 



The subject of what temperatures are reached in the ahead elements with the turbine 

 running astern is an important one, particularly should the vacuum be low. 



Experiments have been made with a 1,500 horse-power, 3,600 revolutions per minute 

 Westinghouse marine equipment, which gave the temperatures shown by the curve 

 on Plate 122. 



Mr. Parker M. Robinson^ Visitor: — There seems little doubt but that electric drive 

 is the next logical step in marine propulsion. Electrical apparatus has been developed to 

 such a fine degree in a great many lines of industrial and power-house work that there 

 should be little difficulty in making the application to marine work absolutely satisfactory. 

 The advantages are, of course, very great for the larger ships, especially the battleships, 

 when flexibility and economy at cruising speeds are considered. However, when applied 

 to a typical merchant vessel of approximately 3,000 shaft horse-power, the advantages are 

 by no means soi marked. Perhaps for this service the Diesel electric drive promises the 

 best results. 



One of the main disadvantages to the electric drive which Mr. Emmet mentioned, 

 and which has probably been reiterated more often than any other, is the problem of get- 

 ting the operating engineers to understand the apparatus and handle it intelligently. 



The same criticism was made of the geared turbines, and to a certain extent it was 

 true. Marine engineers in general are rather inclined to be consen^ative and are naturally 

 prejudiced against any new piece of apparatus. The majority of ships driven by geared 

 turbines have been commissioned since the beginning of the war, and in the necessity for 

 haste, vessels have often been sent to sea with engineers in charge of them who had been 

 given no opportunity at all to familiarize themselves with the equipment which they were 

 to operate. It is no wonder that troubles occurred. The only wonder is that there were 

 not more break-downs. 



