March i, 1900] 



NATURE 



427 



reisons of economy and also of time (as many alterations were 

 anticipated), to build as small a vessel as possible, but not so 

 small as to preclude the attainment of an unprecedented high 

 speed in the event of success. The Turbinia was constructed, 

 her dimensions being lOO feet in length, 9 feet beam, 3 feet 

 draught of hull, and 44 tons displacement. She was fitted with 

 a turbine engine of 2000 actual horse-power, with an expansive 

 ratio of a hundred-and-fifiy-fold, also with a water-tube boiler 

 of great power, of the express type, with small tubes. The 

 turbine engine was designed to drive one screw shaft at a speed 

 of from 2000 to 3000 revolutions per minute. 



Many trials were made with screw propellers of various sizes 

 and proportions, but the best speeds were quite disappointing, 

 and it was clear that s-^me radical defect lay in the propellers. 

 This was corroborated by dynamometric measurements. The 

 excessive slip of the propellers beyond the calculated amount, 

 and their inefticiency, indicated a want of sufficient blade area 

 upon which the thrust necessary to drive the ship was dis- 

 tributed, in other words, the water was torn into cavities behind 

 the blades. These cavities contained no air, but only vapour of 

 water, and the greater portion of the power of the engine was 

 consumed in the formation and maintenance of these cavities 

 instead of the propulsion of the vessel. This phenomenon was 

 first noticed in the trials of the torpedo boat Daring, by Messrs. 

 Thornycroft and Mr. Barnaby, shortly before the commence- 

 ment of the trials of the Turbinia, and was named " cavitation " 

 by R. E. Froude. 



To return to the Turbinia, a radical alteration was deemed 

 necessary. A new turbine engine was made, consisting of three 

 separate engines, high pressure, intermediate pressure, and low 

 pressure, each of which drove one screw shaft, the power of the 

 engine was distributed over three shafts instead of being concen- 

 trated on one, and three propellers were placed on each shaft. 

 The result of these changes was marvellous. The vessel now 

 nearly doubled her speed, 30 knots was soon reached, and 

 finally 32^ knots mean speed on the measured mile authenti- 

 cated, or the fastest speed then attained by any vessel afloat. 

 The economy of her engines was investigated by Prof. Ewing, 

 assisted by Prof. Dunkerly, the consumption of steam per indi- 

 cated horse-power for all purposes at 31 knots speed was found 

 to be 14 A lbs., or in other words, with a good marine boiler the 

 coal consumption would be considerably under 2 lbs. per indi- 

 cated horse-power, a result better than is obtained in torpedo 

 boats or torpedcf-boat destroyers with ordinary triple expansion 

 engines. 



The vessel's reversing turbine gave her an astern speed of 6^ 

 knots, and she could be brought to rest in 36 seconds when run- 

 ning at 30 knots speed, and from rest she could be brought 

 up to 30 knots in 40 seconds. 



The Turbinia cruised from the Tyne to the Naval Review at 

 Spithead, where she steamed on the day of the Review at an 

 estimated speed of 34^ knots. These results represent about 

 2300 indicated horse-power, and may be said to have been 

 obtained without a very abnormal performance as regards the 



Fig. 3. — Turbine engines of the Viper 



This phenomenon has been investigated experimentally with 

 propellers of small size working inside an oval tank, so as to 

 represent approximately the conditions of slip ratio customary 

 in fast ships. To enable the propeller to cause cavitation more 

 easily the tank is closed, and the atmospheric pressure removed 

 from the surface of the water above the propeller by an air- 

 pump, gl.ass windows are fitted for observation and illumination. 

 Under these conditions the only forces tending to hold the 

 water together and resist cavitation are the small head of water 

 above the propeller, and capillarity. The propeller is 2 inches 

 diameter and 3 inches pitch ; cavitation commences at about 

 1200 revolutions and becomes \%ry pronounced at 1500 revolu- 

 tions. Had the atmospheric pressure not been removed, speeds 

 of 12,000 and 15,000 revolutions per minute would have been 

 necessary, rendering observations more difficult. 



The arrangement we have now was kindly suggested by Mr. 

 Heath, and is a decided improvement, the revolving disc with 

 narrow slots synchronising approximately with the revolutions 

 of the propeller. The propeller is now seen to rotate very 

 slowly. It also permits of the projection of the phenomenon on 

 the screen, which was not possible with my previous arrange- 

 ment. The permanence of the vortices behind the blades is 

 wry striking. The inference to be drawn from these experi- 

 ments seems to be that for fast speeds of vessels, wide thin 

 blades, a coarse pitch ratio, and moderate slip, are desirable for 

 the prevention of cavitation, and in order to obtain the best 

 efficiency in propulsion of the vessel. 



NO. 1583, VOL. 6lj 



boiler ; its total heating surface being iioo square feet, and an 

 evaporation of about 28 lbs. per square foot at the speed of 34J 

 knots. 



These speeds were not obtained by bottling up the steam and 

 opening the regulating valve on coming to the measured mile, 

 but were maintained for many miles together with constant 

 steam pressure, and as long as the fires were clean. On the 

 other hand, the endurance of the engines themselves seems to 

 be unlimited, all heavy pressures, including the thrust of the 

 propellers, that would in ordinary engines came on the bearings, 

 being counterbalanced by the steam pressure acting on the 

 turbines. 



It seems clear that the results obtained in the case of the 

 Turbinia were almost entirely due to the economy in steam of 

 the turbine engines, and the unusually small weight of the 

 engines, shafting and propellers', in proportion to the power 

 developed. 



It may also be said that generally speaking every part 01 

 the machinery was as substantial as in naval vessels of the 

 torpedo-boat class, yet she developed 100 horse-power per ton 

 of machinery, and 50 horse-power per ton of total weight of 

 vessel in working order. 



The results of the Turbinia having been found satisfactory, 

 the original company which built her was merged into a large 

 company under the same directorate for carrying on the work 

 on a commercial scale. At Wallsend-on-Tyne, the Parsons 

 Marine Steam Turbine Company erected works, and in 1898 



