176 ELECTRIC AUXILIARIES ON MERCHANT SHIPS. 



assume that this steam is passed into the low-pressure element of a Parsons turbine and ex- 

 panded from 5 pounds gauge to 28^ inches vacuum. It is assumed that superheated steam 

 (75 degrees) is supplied to the auxiliaries; that it is approximately saturated upon arrival 

 at the turbine; and that the exhaust pressure is reduced from 10 to S pounds. With satu- 

 rated steam, the slow-pressure turbine will develop a horse-power on 23 pounds of steam, 

 so that 346 horse-power .could be developed by the steam which is wasted. This represents 

 about 14 per cent of the total power of the turbine. It is needless to say that this is not a 

 suitable basis for an accurate comparison. 



The steam consumption given for the airxiliaries is about SO per cent higher than I would 

 estimate it to be for properly designed auxiliaries. It is also noted that this consumption is 

 about 40 per cent of that of the main turbine. I would say that this figure would represent 

 inefificient machinery or performance. 



On page 167, the steam consumption per S. H. P. is given as 16.5 pounds. This is not 

 representative of efficient machinery oi this class, for which the consumption should be 14^ 

 pounds or less. Also, the fuel consumption per S. H. P. is higher than it should be for such 

 machinery with reasonably good operation. 



It is not clear from page 167 whether the turbo-generator is condensing or non-conden- 

 sing, and where the exhaust goes to. It would also be interesting to know the horse-power 

 and other particulars upon which this performance is based. 



On page 169, under "saving in fuel consumption at sea," the author has allowed the same 

 quantity of auxiliary steam for both 75 and 200-degree superheat. This cannot be consid- 

 ered accurate, since the power and steam consumption of the auxiliaries should be approx- 

 imately proportional to the turbine steam consumption in twO' equally well-designed installa- 

 tions. It is not clear, but it is assumed, that the main turbines for both steam and electrical 

 auxiliaries operate under the same steam conditions. Otherwise the comparison would be of 

 little value. 



As pointed out above, 14 per cent in equivalent turbine power is wasted, and conse- 

 quently this comparison cannot be considered as reliable. The same applies to the saving per 

 year. Under this heading, also, no account is taken of depreciation, repairs, etc., which 

 amount to about 12 to 14 per cent of the first cost, which is considerably higher for the elec- 

 trical auxiliaries. 



My conclusions after investigating the subject of electrical auxiliaries for cargo vessels 

 were as follows : 



1. Two large turbo generators were required. 



2. We could not get electrical auxiliaries into the same engine room as used for steam 

 auxiliaries, and additional space had to be allowed. 



3. The electrical auxiliaries were heavier and more expensive than the steam auxiliaries. 



4. The saving in steam and fuel consumption was not sufficient to justify the use of 

 electrical auxiliaries. 



I regret that I cannot give more specific data (including weight, cost, fuel consumption, 

 etc.), since this would be desirable. 



On page 170 it is implied that electric winches will handle cargo faster than steam 

 winches. I do not think this can be considered as an accepted fact. For machinery of the 

 same capacity, I do not believe there will be enough difference to be of importance in the 

 usual class of cargo handling. In special cases there may be advantages of importance, which, 

 of course, should be given due consideration. 



