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September, 1909 Rosoure de Almeida, representing the Brazilian naval commision, and Capt. Affonso de Fenseca Rodrigues, the commander of the vessel, passed off without the slightest hitch, and the TAE Mariné REVIEW Brazilian authorities expressed them- selves as being very highly satisfied with the result. The Parahyba was built by Yarrow & Co., Scotstown, Glasgow. The Steam Turbine and the Reciprocating Engine for Marine Propulsion.' By. Ira NN. Heriis, HE chief difficulty in the way of the steam turbine has been the screw propeller. Certain sacrifices in efficiency have been necessary in adapting the two to each other. While the turbine can be designed for low speed, its size and weight then run up _ too much for marine practice and it no longer compares favorably with the reciprocating engine except in econ- omy. The number of stages in the Parsons machine grow greater as its rotative speed grows less, so that the casings and disks stretch along the shaft inordinately. The inventor found this true even for the high speed at which the turbine was run, and he placed the successive groups of stages in different casings on separate shafts as explained before. The Curtis turbine on the other hand, is usually increased in diameter for low rotative speed. This adds rapidly to the weight of the shaft and becomes prohibitive below a certain speed. We thus have the curious paradox of more turbine for low speeds than for high. Up to this time, no marine turbine has been de- signed for the low rotative speed of the reciprocating engine of freight ships. Given, then, a limit of weight for the power demanded by a ship, the turbine requires for economical performance much higher rotative speed than the steam engine. Its whole efficiency is dependent upon high speed unless ex- cessive weight and complication are permissible. The screw propeller is ex- actly the reverse. It must be run at low speed to avoid great frictional and slip losses. A compromise then follows by which both the propeller and turbine are sacrificed for a speed at which they work together with greatest economy. The truth is that erroneous conclusions are ._ easily reached by separating the two in com- paring the performance of the ships equipped with different types of pro- pelling apparatus. The prime mover 'Late U. S. N. professor of mechanical en- gineering, Harvard University. | oe *Abstracted from Enginecring Magazine. and the propeller treated as a unit. must inevitably be Advantage of Reciprocating Engine at Low Speed. Another consideration is that the turbine falls off more rapidly in effi- ciency than the steam engine as _ the speed decreases. For this reason, it is not specially adapted to war vessels, which usually steam at only half speed. Cruising. turbines have been added by Mr. Parsons, which is only another method of increasing the number of stages for low rotation of the shaft but it is doubtful if even this addi- tion serves the purpose. So far, the reciprocating steam engine has the ad- vantage at low speeds in all classes of ships. A few examples of sister ships us- ing different types of propelling ma- chinery will serve to show the rela- tive rotation speeds. Among these the most interesting are the three scout cruisers, Birmingham, Salem and Chester, fitted respectively with tr.ple- expansion engines, Curtis turbines and Parsons turbines. The data in Ane small table are taken from the ac- ceptance trials, as the results of the recent tests are not yet available for publication. The German cruisers are taken from a paper by Mr. Bauer: 319 © _corded owing to some defect in the measuring apparatus. In the case of the first two German cruisers the shaft power of the Par- sons turbine exceeded the indicated power of the reciprocating engines by 10 per cent while for the second two the reverse was true, the Curtis tur- bine requiring 11 per cent less power on the shaft than the indicated power of the reciprocating engine. Comparisons of this kind are very unsatisfactory, however, as the rela- tion between the indicated horsepower of the reciprocating engine and the effective power on the shaft depends upon too many facts to be well-known for any special case, except after ex- tensive experiments for the purpose of ascertaining accurately the work lost in friction. Besides, it is very dif- ficult to take account of the. effect of different designs of screws upon the hull resistance. No two ships have exactly the same auxiliaries and no two crews ever work with precisely the same efficiency. Consequently no fair bases of comparison have yet been established and the results are likely to be inconclusive. Little Advantage Between 20 and 25 Knots. The only sound conclusion to be reached from the data at hand is that in the matter of power, weight and economy there is little to choose be- tween the reciprocating engine and the turbine for speeds between 20 and 25 knots, with perhaps a preponderance in favor of the latter. Below 20 knots the results are largely in favor of the former. The Birmingham's engines will probably be found to gain over the other two in economy and ease of handling as the speed decreases. But this is not the whole question for a man-of-war. Her maximum speed may Speed Revolutions Fores ee ip. Type of engine. in knots. per minute. of propeller. bags acter ie Pe Gee Reciprocating «-.+-+++-++++- 22:5 21 12.65 2. Birmingham «----++-+++"' Reciprocating .-.+-++-++++ 24.33 191.7 15.8 s Seem vie rt Curtis turbine .....--..-- 22.5 312.5 16.17 A; Salem i. .25+ se oeee ces oe Curtis turbine ...-..---++> 25.95 378 20.23 5S. Chester = si 55s ee recs cic ene Parsons turbine ......-.-- 2265 473 18.46 6. Chester .----seeceetceccs Parsons turbine de cba eee 26.52 614 25.56 7, German cruiser .-----+.-- Reciprocating ...-+-+++++ 23 143 g. German cruiser .---+--++++- Parsons turbine ....-.+--- 23 528 9. German cruiser ..++++-+-+> Reciprocating «-.----+++-- 24 S187 10. German cruiser .-++- eco. Curtis turbine. ..-.-.s.+4 24 335 The total indicated horsepower for all machinery, including auxiliaries, on the Salem was 10,836 at 2214 knots. This was obtained by adding 10 per cent to the shaft horsepower recorded by the torsion meter. On the Birmingham the power for all purposes was practically the same, being 11,098 at 2214 knots. The power on the Chester was not re- be required for only short intervals or in emergencies, but when it is needed it is needed badly; consequently, the machine which will maintain thaz speed reliably will invariably be chosen. There is another aspect of the case for [:at- tleships and armored cruisers and that. is the vibration. A steam engine may be balanced for the reciprocating