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26 are only slightly more economical than turbines when work- ing below about 60. percent of the vessel's full speed (that is, say 12 knots for a 20-knot ship), while above this the tur- bine is superior. Ample and reliable steam consumption data for all classes of warships is now available from trials conducted by the British Admiralty, who have also carried out careful comparative tests on cruisers and torpedo boat destroyers, exactly similar but for their propelling machinery, for the purpose of determining the relative efficiency of the two systems. Similar experiments have been. carried out with channel steamers in a very comprehensive way, and in all cases the actual trials of the ships have been supplemented by elaborate, tank experiments. The result of these investiga- a 1H-P Rpm. Serco tions has been the adoption of the Parsons steam 'turbine for all classes of British warships. ; The cruisers tested were the Topaze and Amethyst, of 3,000 tons. Fitted with turbines, the Amethyst obtained a maximum speed of 1.5 knots more than the Topaze; for the same steam consumption, the speed of the Topaze was 21 khots against the Amethyst's 23, or for 22 knots the consumption per unit of power in the Amethyst was 13.8, and in 'the Topaze, 22 pounds. The progressive trial results are shown in Plate II. Carried out with great care, and corroborated by the simi- lar results obtained from the two sister ships of the Topaze, these long-desired experiments on similar ships, running under similar conditions, did more than demonstrate the superior economy of the turbine at full power. They showed that down to 14 knots the turbine was more economical, and that below 'this speed the difference in favor of the reciprocating engine was by no means as large as had been supposed. In fact,' with the auxiliary exhaust steam being passed "TAE. Marine. REVIEW / through the turbines, the economy is better above 10 knots. Similar results were obtained from the trials of the Midland Railway steamers, which unlike the Amethyst were not fitted with cruising turbines. The greater economy of the turbine _vessels was very marked at high speeds, and only ceased below 14 knots. The question of economy is very important. It is, prob- ably, the crucial point in considering the adoption of tur- bines, and even if the machine possessed no other advan- tages, economical results such as have been obtained -- | Cle 1° yaoi ay Gaal ea Ps Sg 2645 +. an ae gs 7 : Hp APO ed 4 Ll Para t top Z J ¥ " 5 Jw eee Z AA KW LAVA LLZ 2. HT/ af oo [ y mA Z vf 22-36 + S IV VV TIT CAs AAA AIA IAT wa J x / \pnmo or "S9TRSTED aren, ye oa AA 3 a e ee eee undoubtedly entitle it to careful consideration. On Flate. Jil; in Fig. -A, is: given. the: steam --con: sumption per J. H. P. of H. M.S. Amethyst, com- pared with that of other warships over a wide range of speed. Actual steam consumptions of merchant vessels run at low powers are almost impossible to obtain, but seeing that naval -- engines are designed to be most economical at about 8&0 percent of full speed, and that at 50 percent there is such a marked rise in their consumption, there can be little doubt that the performance of merchant en- gines, designed for maximum economy at full power, would be much the same at low speeds as that of the warships. There has been a tendency, due possibly to lack of data, to imagine . that the consumption of ordinary engines at low speeds was not so great as recent trials have shown it to be. Figure B gives the total consumption of the Aamethyst and Topaze plotted on horse-power, while Fig. C gives a similar diagram for two destroyers tried. Fig. D gives the total -