POR AUXILIARY PURPOSES ON BOARD SHIP. 163 



chance as to whether a gear will or will not be satisfactory, or, if initially satisfac- 

 tory, will stay so. 



The noise created by an imperfect gear in the confined spaces on board ship 

 must necessarily be more disagreeable than in a large power-house, and the above, 

 taken into consideration with the really small saving in the over-all economy as 

 pointed out later, leaves the writers very skeptical as to the net advantages. 



Two of the sister battleships now building, the Idaho and the Mississippi; 

 are equipped with direct-connected and geared circulating pumps respectively, and 

 some very interesting comparative results should be forthcoming. Also the com- 

 parative cost of upkeep after twelve months of operation will undoubtedly throw 

 very valuable light on this subject. 



Another innovation was made by Mr. Wetherbee, of the Bath Iron Works, to 

 reduce the unit steam consumption on the blower turbines, viz., by arranging the 

 turbine blowers so that they could be operated either singly or in parallel. For 

 running at full speed the blowers are operated as single units, and at cruising 

 speed they are operated in series. A very marked improvement in economy has re- 

 sulted from this combination. 



One point it might be well to bring out here when considering the question of 

 efficiency, and that is the ease at which the total steam passed by a turbine auxil- 

 iary can be quickly and accurately measured without the aid of any measuring tanks, 

 etc., and it appears to us that this should be extremely useful on trial trip work. 



Practically all small turbines expand the steam in the initial jets to a point 

 below the critical velocity, so that Napier's formula for the flow of steam through 

 jets will give results as accurate and probably more so than any weighing or 

 measuring method. All that is necessary is an accurate gauge placed right in the 

 steam ring and a record taken of the dimensions of the throats of the jets. It will 

 be found that all makers of small turbines are very particular about the design, 

 shape and dimensions of the jets being made to accurate plug gauges so that the di- 

 mensions of the jets can be relied upon with certainty. Napier's formula reads: — 



70 



where W = weight of steam per second. 



P = absolute pressure before the jets in pounds per square inch. 

 A = the area of the jets in square inches. 

 From actual experience it has been found that for the majority of small tur- 

 bine work and the small jets that are necessary for the expansion of high-pressure 

 steam, a coefficient of 72 is more accurate than 70, and this in turn simplifies the 

 formula given for the flow of steam per hour as follows: — 



Wi = SoPA 



where Wi in this case equals the pounds of steam per hour. 



