FOR AUXILIARY PURPOSES ON BOARD SHIP. 157 



The type of fan has evolved from the original Sirocco to the cone type, and 

 then back to the multiblade, with blades of such design as is found will result in 

 quiet running. Whereas, originally on oil fuel for destroyer service, a ratio of 

 225 cubic feet per pound of oil to be evaporated, was considered to be correct, now 

 350 cubic feet per pound is standard. 



This takes care of a greater dilution, coefficient and smokeless burning of 

 the oil as well as leakages. Smokeless operation is one of the principal points on 

 torpedo-boat maneuvers, and in order to accomplish this in many ships an exces- 

 sive amount of air is forced into the boiler rooms, even at a sacrifice of fuel econ- 

 omy. Photographs of early destroyers taken on trial as compared with that of the 

 Ericsson show a marked difference in this respect. 



Little authentic information could be obtained at first from fan-builders as 

 to the absolute and true performance of the fans, and therefore there was nothing 

 left to do but to run comparative tests. In September, 191 1, three different types 

 of fans were tested out on a comparative basis. These tests were fully described 

 in the Journal of the American Society of Naval Engineers, Vol. XXIV, No. 4. 



As mentioned in the description of these tests, no attempt was made to deter- 

 mine the true performance of the fans and only comparative results were looked 

 for. In a later number of the same journal these tests were severely criticised by 

 Mr. Schmidt, but in the meanwhile, before the publication of Mr. Schmidt's paper, 

 further tests had been carried out on a modified box at the Terry plant and also 

 very careful tests were carried out on board ship. These tests were very instruc- 

 tive, and a brief description of the same is given in the appendix of this paper. 



The turbine-driven fan has proved so eminently satisfactory in destroyer work 

 that the reciprocating engine is no longer considered. In all there are now forty- 

 six oil-burning destroyers with turbine driven forced-draft fans, each with four 

 complete units. Out of this number the Terry Company have supplied thirty- 

 eight, and to date we have only a record of two actual repairs necessary to thd 

 machines due to any defects whatever, not of course considering the wear and 

 tear of bearings, etc. This successful application of the turbine fan to destroyers 

 has resulted in an entire change of policy in battleship work and smaller boats, 

 also in the mercantile marine. The motor-driven fan, so long considered the stand- 

 ard for battleship work, is making way for the turbine blower. 



For battleship work the horizontal-turbine drive is now standard in the U. S. 

 Navy, as replacing the motor-driven sets, because of its reliability, ease of control 

 direct from the fire-room, and also that it is not dependent upon intermediary ma- 

 chinery — electric generators. Plate 74 shows such a unit connected to a double- 

 inlet fan. 



A higher efficiency can be maintained on the cased fan than on the open type, 

 and also the double inlet can be used, thus obtaining higher speeds for correspond- 

 ing static pressures as compared with the single-inlet open fan. 



Capacity and total steam curves of a recent unit of this type are given in 

 Plate 75. At a rating of 17,500 cubic feet per minute and 6 inches static pressure 



