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June, 1909 the effective horsepower required from the results of tank experiments, that we are able to estimate the effi- ciency of turbine-driven propellers. The figures for propeller efficiency obtained from the trials of model propellers working in undisturbed water are almost valueless when ap- plied to actual practice. Efficiency of Mauretania's Propellers. In the case of the Mauretania, al- though the propellers were very care- fully designed, and are the result of long and elaborate experiments and comparisons, it is doubtful if their efficiency is over 52 per cent. The efficiency of the Lusitania's pro- pellers has been given as 48 per cent, and it must be remembered that these screws are working under con- ditions very favorable to the turbine propeller. The efficiency of the propellers fitted to turbine cross-Channel steam- ers may vary from 48 to 52 per cent, while those of turbine-driven torpedo boats and destroyers cannot be much more that from 45 to 48 per cent efficiency. Let us compare these figures with the efficiencies obtained with the slower running screws of reciprocat- ing-engined vessels. Here the effici- ency may be said to vary from 60 to 66 per cent in most-cases, only drop- ping much below 60 per cent in the case of the bluff-sterned single screw cargo tramps, in which case it may be as low as 55. per cent. With the assistance of these figures we can estimate approximately the steam consumption per thrust horsepower per hour, and so obtain a truer com- parison as regards the economy of the two systems. "TAE Marine REVIEW it must be conceded. that consid- erable modifications would be neces- sary to affect the general conclusions. Turbine and Naval Vessels. As regards the machinery of naval vessels the table shows a marked superiority for the turbine system with reference to economy. Thus the increase in steam consumption with reciprocating engines would ap- pear to be about 14 per cent with battleships and the heavier classes of cruisers, and as. much as '20. per cent with the lighter and less effi- cient engines of small cruisers and scouts; while as regards torpedo craft the turbine © system. 1) only slightly more economical. In other respects also the steam turbine is admirably suited to the requirements of naval work, It requires very little attention and no great skill in operating, qualities which may be of great importance in action, and also in view of the fre- quent changes in the engine room staff. Full power can be easily 'main- tained with the turbine, whereas, in. the piston engines fitted to the latter classes of warships the bearing sur- faces were generally deficient, and very careful attention on the part of a- numerous staff was necessary at ° anything approaching full _ speed, while very gradual working up was essential. Another quality of the tur- bine which is of great importance in naval work is its suitability for working at any proportion of full power.' On the other hand, the pis- ton engine shows to best advantage when worked at one unvarying speed. When all these considerations are taken in conjunction with the advant- Naval or Turbines or Steam per shaft Steam per thrust merchant vessels. Type of vessel. recip. engines. horsepower Propeller horsepower : per hour. efficiency. per hour. ( Lb. Per cent. Lb. Battleships and Turbines ....... 14.5 50 29 large cruisers Recip.* engines... 1955 60 32.5 Naval vessels..4 Small cruisers Turbines ....... 14.5 50 29 and scouts Recip. engines... 21 60 30 'Torpedo craft Turbines: ......% 16 47 34 L Recip. engines... 21.5 60 36 ( High-speed cross-Channel Turbines ....... 14.5 50.5. 2 ; steamers Recip. engines... 19,5 60 32. Merchant ' 2 . Vessels. . s.°;. 4 High-speed TAPE DINIES. 35s fs os 14 ocean liners Recip. engines... 15.875 64 24.8 Intermediate Turbines ...... : 14.25 52 27,5 | ocean liners Recip. engines... 15.25 65 23.5 The above table is rather instructive as indicating the limit which the high-speed propeller sets to the ef- ficient application of the turbine sys- tem. Of course, the figures in the table are > necessarily approximate, but they represent fair averages, and age of lying very low in the ship, the overwhelming superiority of a turbine system for this class of work cannot be questioned. With regard to merchant vessels, however, the sit- uation would appear to be very dif- ferent. The table shows the turbine 'System 135 to considerable when applied to high-speed cross- Channel steamers, and actual prac- tice supports this conclusion. In this case the table indicates an increase of 12 per cent in the steam consump- tion when piston engines are adopted. advantage Steam Consumption on Racing Liners, On the other hand, when we con- sider the case of high-speed racing liners, it would seem that the con- sumption of steam per thrust horse- power is about 9 per cent greater when turbines are fitted, so that the advisability, of applying turbines to this class of vessel appears somewhat doubtful. Again, in comparison with the highly efficient reciprocating en- gines of the intermediate type of ocean liner, the turbine system ap- pears distinctly inferior in economy as the increase in steam consumption when turbines are adopted appears to. be about 17 per cent. There seems to be considerable reason to believe that this conclusion is supported by the actual results obtained with turbine vessels of this -- class. Thus there exists little doubt in the minds of many engineers that better results with reduced expenses would have resulted had piston' en- gines been fitted in the express Cu- narders.' Again, a significant silence is maintained regarding the perform- ance of the slower-speed_ turbine liners, and there are persistent re- ports of excessive coal consumption. In this connection a comparison of the coal consumption of the Carmania with that of her reciprocating-en- gined sister Caronia would be very interesting, and possibly instructive. Apart from the question of economy, the turbine is not seen in so favora- ble light when compared with the piston engines of the ocean liner. With ample bearing surfaces no great difficulty is experienced in main- taining full speed with this type of engine. Again, the speed remains practically unaltered when at sea-- a condition which shows the recipro- cating engine at its best. On the other hand the turbine is a very much simpler machine. The wearing parts are very few and the wear scarcely perceptible. The lubrication is automatic, so that a considerable saving in attention and oil must re- sult. Then, as the wearing parts are few, the depreciation with the turbine should be very slight. The point to be considered is whether these advantages can compensate for an in- crease of from 9 to 17 per cent on the coal bill.