t>ROGRESS IN TURBINE SHIP PROPULSION. 85 



The author's paragraph dealing with maneuvering valves is interesting, for he tends to 

 show it is a special advantage to have the turbines operated automatically rather than by brain 

 control. 



Personally, I strongly favor having separate valves for ahead and astern turbines, for 

 it gi\es the operator a little more to do and makes him fix his attention on the work in hand. 



The piping diagram (Plate 32), to my mind, is somewhat complicated, and I do not at all 

 like the idea of having the shut-ofif valves in each pipe line, either for the high-pressure pipes 

 or the exhaust steam lines. These valves, fitted as shown, are solely for emergency con- 

 ditions, and unless they are kept in working order they are generally found useless when the 

 unusual occasion arises. 



In conclusion, it is of special interest and significance to note that the reliability of the 

 rigid bearing type of turbine-driven mechanical reduction gearing has been firmly estab- 

 lished. Sir Charles A. Parsons and his associates have already placed in successful operation 

 over 7,000,000 horse-power of gears built in this manner. 



Mr. Hodgkinson :— Replying to Mr. Emmet, I do not know of any troubles that have 

 been experienced with well-designed turbines, due to them being provided with reversing 

 elements, although there are instances of injury due to operating astern for long periods 

 with low vacuum, when, of course, serious heat is generated in the ahead elements. 



Neither have I observed, in the case of floating frame gears, with which I am most 

 familiar, the slightest difference, so far as behavior of the machinery is concerned, whether 

 the machinery be installed aft or amidships. I know of one tanker with machinery aft whose 

 stern tube became injured, the shaft wearing down a total of 1% inches through the wood 

 and bronze and into the cast iron shell of the tube itself, the effect of which was to cause 

 no disturbance whatsoever to the operation of the gear. 



Concerning the use of superheat, the modern high-speed geared turbine, as pointed out 

 in the paper, is far more sensible of operating with high superheat than was the older direct- 

 connected drive. What is the limiting temperature with a view to both economy and re- 

 liability will, I think, be largely determined by personal judgment. The desirable amount 

 of superheat is not necessarily less for high-speed geared turbines than for those employed 

 for the electric drive. 



Mr. Emmet refers to the S. S. Mjolner, wherein with 300 degrees superheat, 38 per 

 cent gain in fuel consumption was observed over her sister ship, without saying anything 

 about the machinery of the sister ship. Of course the whole of the 38 per cent was not 

 because of superheat ; there were other reasons. The S. S. Maui, for example, with but 50 

 degrees superheat, secured a gain of 22.8 per cent over her sister ship, her sister being a 

 single-screw, triple-expansion reciprocator ; the Maui a twin-screw steamer, each shaft 

 driven by cross-compound geared turbines. 



I am appreciative of Mr. Sanford Riley's remarks, and in the course of our 

 work in marine installations we are indebted to both Mr. Riley and other engineers of the 

 Technical Staff of the Fleet Corporation for their timely suggestions and co-operation. Mr. 

 Riley refers to unavoidable leaks in coolers. There is indeed always the danger of a split 

 tube which may admit salt water to the oil, or loss of lubricant, according to whichever ele- 

 ment is at the higher pressure. I do not think tube packings, as ordinarily understood, should 

 be employed. The tube should be rolled into the tube plates and proper means provided 

 for expansion, as may readily be done. 



