582 thp: progress in stp:am navrjation. 



special design supplies .stetiiii of 175 pounds pressure, and is exception- 

 ally light for the steam produced, being highly forced. 



The whole weight of machinery and boilers is 23 tons. In other 

 words, about 100 horsepower indicated is produced for each ton weight 

 of propelling apparatus. This is rather more than twice the propor- 

 tion of power to weight, as compared with the lightest machinery and 

 boilers fitted in torpedo boats and dest^o^'ers. It will be noted that in 

 the Tarhlnifu as in the destroyers, about half the total weight is 

 devoted to propelling apparatus, and in both instances the load carried 

 is relatively small. The secret of the extraordinary speed is to be 

 found in the extreme lightness of propelling apparatus and small load. 

 No (l()ul)t in the Turhinin lightness has been })ushed further than it 

 would be in vessels of larger size and greater [)()wer. In such vessels 

 a lowei' rate of revolution would ])r()bably be accepted, additional 

 motors would be fitted for maneuvering and going ast(M'n. boilers of 

 relatively greater weight would be adopted, and other changes made. 

 Bui after making ample allowance for all such increases in weight, it 

 is uniiuestionable that considerable economies nuist be possible with 

 rotary (Migines. Two other vessels of the destroyi'r type witli turl)0 

 motors one for the royal navy — are now approaching completion. 

 Their trials will be of great interest, as they will furnish a direct com- 

 parison with vessels of similar size and f(^rm fitted with similar boilers 

 and driven by reciprocating engines. 



On the side of coal consumption Mr. Parsons claims at least equality 

 with the best triple-expansion engines. Into the other advantages 

 attending the use of rotary engines it is not necessary now to entcn*. 

 Reference must be made, however, to one matter in which Mr. 

 Parsons has done valuable and original work. In torpedo vessels of 

 high speed the choice of the most efficient propellers has always 

 been a matter of difliculty, and the solution of the problem has in 

 many instances inv^olved extensive experimental trials. B}^ means of 

 alterations in propellers alone very large increases in speed have been 

 eti'ected; and, even now, there are difficulties to be faced. When Mr. 

 Parsons adopted the extraordinary speed of revolution just named for 

 the Turhhila he w^ent far beyond all experience and precedent and had 

 to face unknown conditions. He has found the solution after much 

 patient and original investigation in the use of multiple screws of small 

 diameter. His results in this direction are of general interest to all 

 who have to deal with screw propulsion. Such radical changes in pro- 

 pelling machinery as are involved in the adoption of turbo motors must 

 necessarih^ be subjected to thorough test before the3^ will be widely 

 adopted. The experiment which the Admiralty are making is not on 

 a small scale as regards power. Although it is made in a destroyer, 

 about 10,000 horsepower will probably be developed, and a corre- 

 spondingly high speed attained. It may well happen that from this 



