848 REPORT—1899. 
in this review without a brief notice, This rotary engine, with its very high rate 
of revolution, reduces the weights of machinery, shafting, and propellers greatly 
below the weight required in the quickest-running engines cf the reciprocating 
type. This reduction in the proportion of weight to power carries with it, of 
course, the possibility of higher speed in a vessel of given dimensions; and when 
large powers are employed the absolute gain is very great. An illustration of this 
has been given by Mr. Parsons in the Twrbinia. That remarkable vessel is 
100 feet long and of 443 tons displacement, but she has attained 33 to 34 knots in 
short runs. There are three shafts, each carrying three screw propellers, each 
shaft driven by a steam turbine making over 2,000 revolutions at full speed, when 
more than 2,000 horse-power is developed. A water-tube boiler of special design 
supplies steam of 175 lbs. pressure, and is exceptionally light for the steam 
produced, being highly forced. The whole weight of machinery and boilers is 
22 tons: in other words, about 100 horse-power (indicated) is produced for each 
ton weight of propelling apparatus. This is rather more than twice the proportion 
of power to weight as compared with the lightest machinery and boilers fitted in 
torpedo boats and destroyers. It will be noted that in the Twrbinia,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 extra- 
ordinary speed is to be found in the extreme lightness of propelling apparatus, and 
small load. 
No doubt in the 7zbinia lightness has been pushed further than it would be in 
vessels of larger size and greater power. In such vessels a lower rate of revolution 
would probably be accepted, additional motors would be fitted for manceuvring 
and going astern, boilers of relatively greater weight would be adopted, and 
other changes made. But, after making ample allowance for all such increases in 
weight, it is unquestionable that considerable economies must be possible with 
rotary engines. Two other vessels of the destroyer type with turbo-motors (one 
for the Royal Navy) are now approaching completion. Their trials will be of 
great interest, as they will furnish a direct comparison with vessels of similar size 
and form, 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 enter, 
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 difficulty, and the solution 
' of the problem has in many instances involved extensive experimental trials. By 
means of alterations in propellers alone, very large increases in speed have been 
effected; and even now there are difliculties to be faced. When Mr. Parsons 
adopted the extraordinary speed of revolution just named for the Turbinia, he 
went 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 propelling machinery as are involved in the adoption 
of turbo-motors must necessarily be subjected to thorough test before they will be 
widely adopted. The experiment which the Admiralty are making is not on a 
small scale as regards power. AJthough it is made in a destroyer, about 10,000- 
horse-power will probably be developed and a correspondingly high speed 
attained. It may well happen that from this experiment very far-reaching effects 
may follow. Mr. Parsons himself has prepared many designs illustrating various 
applications of the system to sea-going, cross-Channel, and special service vessels. 
Where shallowness of draught is unavoidable the small diameter of the screws 
possible with the quick-running turbines is clearly an important matter. 
Comparisons between Large and Small Vessels. 
It has been shown that the attainment of very high speeds by vessels of small 
size invelves many conditions not applicable to large sea-going steamships. But 
