DISCUSSION ON MAY MEETING PAPERS. 27 



replacement possibly will be of advantage, but in most cases I think it would not be profitable, 

 considering that tlie average book value of vessels is considerably below the first cost. In 

 the average steam engine or turbine vessel, I believe it would prove more profitable to install 

 superheaters. This can be done at comparatively small expense and will result in a saving 

 of fuel of between 15 and 17 per cent. 



On page 9 the authors recommend twin screws for new vessels of over 5,000 tons 

 deadweight. Considering the types of oil engines in general service at present, this view 

 is concurred in; but if a satisfactory engine is developed for single-screw propulsion, this 

 type will no doubt be preferable, for the reason that the installation will be considerably 

 lighter, less expensive, and the operating staff will be reduced. Our investigation of this 

 subject shows a marked advantage for a single-screw installation for the usual cargo vessel. 



Referring to the difference in cost between the motor and turbine vessel on page 9, 

 the relative values given are considerably different from what we have found. The cost per 

 ton as given is 10 per cent more for the motor vessel ; it is not stated, but I presume this 

 is per deadweight ton. We found a difference of about 40 per cent more per deadweight 

 ton, and about 28 per cent more per ton of average cargo capacity, allowing for fuel, etc., 

 based on a long voyage. 



In this connection, it may be noted that there are differences in the two vessels which 

 influence these values. The vessel in the table has 3,000 tons more deadweight, smaller 

 engines, and apparently lighter auxiliary machinery. 



With reference to the cost of fuel oil, the authors use a difference of 15 per cent. Our 

 information, which was obtained about a year ago, showed an average difference of about 

 25 per cent between 12 to 16 degree steam oil and 18 to 22 degree Diesel oil. 



The voyage selected by the authors for the comparison is a long one and is therefore 

 more favorable to the Diesel engine. It should be kept in mind that this comparison cannot 

 be applied generally and only holds good for the particular conditions given. 



The speed of the turbine propeller is quite low, whereas the engine speed is quite high. 

 The weight of the turbine installation is therefore greater relatively than it should be. We 

 made a comparison for a 12-knot vessel using 90 revolutions for the turbine and 105 for 

 the oil engine. The weight given in the table for the turbine installation wet is 515 

 pounds per shaft horse-power, or 27 per cent more than the weight of our turbine installa- 

 tion, which is 405 pounds per shaft horse-power. The weight given by Mr. Warriner in his 

 paper is 470 pounds, and if allowance is made for boilers and auxiliaries which are too large, 

 and considering the fact that this is a twin-screw vessel, his figure would be reduced con- 

 siderably. It would therefore appear that the turbine weights as given are rather high. 



The oil consumption of our turbine was 1.08 pounds per shaft horse-power, with the 

 following conditions at the turbine : Steam pressure 200 pounds gauge, superheat 25 degrees, 

 vacuum 28^ inches. 



The authors give a consumption of 0.95 poimd of oil for the turbine, the steam condi- 

 tions not being mentioned. I presume, however, that a moderate degree of superheat is 

 used. This is a good performance for the turbine, but it is not the best which can be obtained 

 by using a higher degree superheat of about 200° F. 



The oil consumption of the Diesel engine is 0.40 pound per shaft horse-power for all 

 purposes. This is a good average performance for the main engines only and is the value 

 which we used in our comparison. For all purposes we allowed 0.45 pound per shaft horse-' 

 power, which includes the auxiliary engines and donkey boiler. 



