February 25, 1909J 



iWA TURE 



505 



Steam Turbine Co., Ltd. The success of this vessel soon 

 led to the adoption of turbines in cross-Channel steamers, 

 and also led, aided by the success of the destroyers Vi^er 

 and I'c/o.v, to the specification ol turbines in H.M.S. third- 

 class cruiser Amethyst, and from that time turbines began 

 to be rapidly adopted for fast vessels, including the largest 

 and fastest mercantile and war vessels afloat. 



The success of the King Edward in igoi was a red- 

 letter day for the marine turbine. Let us inquire in what 

 this success consisted. In the first place, a factor of 

 /■rimary importance is the coal bill, and it was soon proved 

 >y Messrs. Denny that this was less to the extent of from 

 S per cent, to 25 per cent, than with vessels propelled by 

 rt'iprocating engines of equal displacement and carrying 

 ■capacity. Also the cost of oil, which with reciprocating 

 ■engines amounts to about 5 per cent, of the coal bill, was 

 nearly eliminated ; the vibration was also less. Then the 

 upkeep of machinery was found to be favourable, and as 

 the crew became accustomed to her the coal consumption 

 still further diminished, and 1 am informed by Captain 

 Williamson that this further decrease has been well main- 

 'tained up to the present time. The exceptional trust- 

 worthiness of the machinery also became more and more 

 assured. 



There are now about 120 vessels actually on service 

 fitted with turbines, and seventy more under construction, 

 representing a total horse-power of marine turbine engines 

 of about 2,250,000, of which 1,250,000 horse-power is 

 ■completed. 



There were two other great steps in the adoption of the 

 turbine, which occurred almost simultaneously in 1905, 

 namely, the decision of the .Admiralty to adopt turbines for 

 all new construction in fighting ships, and the adoption 

 ■of turbine machinery for the great Cunarders. The steps 

 from the second-class cruiser Amethyst, of 15,000 horse- 

 power, to the Dreadnought, of 22,000 horse-power, and to 

 the Indomitable, of 41,000 horse-power, were, it is true, 

 gradual, but the number of vessels involved was great. In 

 the mercantile marine tbe step from the Queen, the first 

 ■cross-Channel vessel, of 8000 horse-power, directly to the 

 Lttsitania and Maitretania, of 70,000 horse-power, required 

 great courage on the part of the late Lord Invcrclyde and 

 his co-directors and engineers. Such steps as these are 

 not taken without thorough investigation based on ascer- 

 tained results. When it is considered that the low-pressure 

 turbine in the Queen was 6 feet in diameter, 20 feet in 

 length, and 25 tons in weight, as compared with the 

 Cunarders' low-pressure turbines of about 17 feet 6 inches 

 diameter, 50 feet in length, and 300 tons weight, it is 

 realised what a great departure was involved ; forces and 

 •conditions were altered ; differential expansions and deflec- 

 tions of the structure had all to be re-considered in detail, 

 for though they had been successfully dealt with and con- 

 trolled in the smaller eiigine, the magnitude of the larger 

 structure rendered re-calculations and thorough investiga- 

 tion necessary ; thus no room was left for the possibility 

 of any adverse conditions arising, due to the very great 

 increase in the size of structure, and everything that care, 

 'thought, and experience could accomplish was done, and 

 the results have satisfactorily agreed with the hopes and 

 estimates of all concerned. 



In the King Edward there was a great increase in the 

 ratio of expansion beyond that hitherto realised in any 

 reciprocating engine. Her boiler pressure is 150 lb., and 

 the pressure at the inlet to the turbines at normal full 

 speed 130 lb. ; the pressure in the condenser is li lb. abso- 

 lute, a ratio of 87 by pressure or about 66 by volume, as 

 compared with the volumetric ratio of about 10 in triple- 

 expansion reciprocating engines for a similar class of 

 vessel. 



In some later turbine vessels higher steam pressures have 

 been adopted, resulting in a small gain in eflSciency, partly 

 counterbalanced by the greater weight of the turbine cases, 

 and if the vessel has Scotch boilers, then also by the 

 ■greater weight of the boilers to carry the greater pressure ; 

 and on the whole the net gain, if any, is but small. 



A substantial increase in efficiency has, however, been 

 realised by improvements in condensers and pumps, in order 

 to take full advantaije of the propertv of the turbine of 

 <'xpanding steam usefully to the lowest pressure attainable 

 in the condenser. Before the turbine came into use a very 



NO. 2052, vor.. 79] 



high vacuum was not found desirable, for the simple 

 reason that the reciprocating engine is unable to utilise it. 

 l'"or instance, a triple-expansion engine does not gain in 

 economy of coal if the absolute pressure in the condenser 

 be diminished below 2j lb. The turbine, however, derives 

 a net gain in efficiency of 13 per cent, from a diminution 

 of pressure in the condenser from 2j lb. absolute to i lb. 

 absolute. 



The improvements that have been introduced of late 

 years in condensing plants consist primarily in improved 

 design of the condenser and in improvements in air pumps 

 to increase their volumetric capacity. In the condenser 

 the tubes are so spaced and grouped that the steam, 

 attenuated into relatively an enormous volume, shall pass 

 freely without much resistance and drop of pressure 

 throughout the whole surface, and provision is made by 

 the form of the condenser shell, with or without a single 

 baffle plate, so that the suction of the air pump shall 

 remove the air uniformly from all parts. The vacuum 

 now usually obtained in well-equipped turbine vessels is 

 very close to that corresponding to the temperature of the 

 circulating water leaving the condenser. The difference 

 is sometimes so small as two degrees, so that there is 

 no room for much further improvement in this direction. 

 To increase the volumetric capacity of the air pumps, dry 

 air pumps run at a high speed may be used, separate 

 pumps being employed to remove the water of condensa- 

 tion. An alternative, and perhaps a preferable method, is 

 the vacuum augmenter, a simple apparatus without moving 

 machinery, which consists of a very small steam jet placed 

 in a narrowed portion of the ordinary air-pump suction, 

 which sucks the air out of the condenser and compresses it 

 through a small intermediate cooler into the suction of the 

 air pump, the water of condensation draining by gravity 

 through a water seal into the same air-pump suction. 



Further possible improvements would therefore seem to 

 tend in the direction of an increase in the efficiency of 

 the turbine itself. In large turbine vessels the ratio of 

 the shaft horse-power to the total available energy in the 

 steam from boiler to condenser reaches 70 per cent., and 

 the question is whether there is a probability of somewhat 

 reducing this loss of 30 per cent. 



During the last eleven years a small reduction in steam 

 per horse-power delivered to the shaft has been brought 

 about by minor improvements in design, better finish and 

 proportion of the blading, and by the increased size of the 

 engine constructed. 



In 1897 the Ttnbinia consumed 16 lb. per shaft horse- 

 power for all purposes ; in 1901 the King Edward consumed 

 16 lb. per shaft horse-power for all purposes; in 1907 the 

 Litsitania consumed 12 lb. per shaft horse-power for all 

 purposes; and the Mauretania consumed 11. 5 lb. per shaft 

 horse-power for all purposes. 



In the case of slow vessels, where the exigencies of the 

 screw propeller limit the revolutions to a low rate, I have 

 for many years advocated a combination or partnership 

 between the reciprocating engine and the turbine which 

 seemed to promise a high degree of efficiency and to suit 

 all the requirements of the case. In this combination 

 each engine deals with that part of the expansion for 

 which it is best suited, the reciprocating engine taking 

 the high-pressure portion from the boiler pressure down 

 10 about atmospheric pressure, and the turbine carrying 

 on the expansion from about atmospheric pressure right 

 down to the condenser pressure. 



The reciprocating engine is thus relieved of the low- 

 pressure part of the expansion, which at best it carries 

 out in a very inefficient manner, losing as it does all the 

 last part, and the turbine is relieved from the high-pressure 

 part, which when constructed for slow revolutions it per- 

 forms unsatisfactorily ; but the turbine designed for low 

 pressures and slow revolutions is an engine which converts 

 a very high percentage of the power in the steam into 

 shaft horse-power. 



Messrs. Denny have fitted the Otaki, of Sooo tons, 5000 

 horse-power, and 13 knots sea speed, with this system, the 

 boiler pressure being 200 lb., no superheaters being fitted, 

 and the very low consumption of 123 lb. of steam for all 

 purposes was registered on trial. Messrs. Harland and 

 Wolff are also fitting a vessel for the Dominion Line on 

 this svstem. 



