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28 _ MARINE REVIEW TWIN VS. TRIPLE SCREWS. Sir William White Holds that the Advantage is with Twin Screws up to 40,000 H. P.--A Noble Defense of the Water=Tube Boiler--Con- tinuation of the story of Ship Development. The Review in its issue of Dec. 10 brought the address of Sir William Henry White, president of the British Institution of Civil Engineers, down to the point wherein he discussed the development of the torpedo boat--small, swift boats with en- gines and boilers of remarkable lightness in proportion to the power developed. Next he took up the turbine. The only ex- cuse which the Review has for endeavoring to completely epi- tomize this address is the fact that no man has more sensibly influenced ship building during the past forty years, and in his address he endeavored to recount his entire career as a ship builder. On the subject off steam turbo-motors he said: "The steam turbo-motor, first applied to ship propulsion by Mr. Charles Parsons in the Turbinia, enables a further saving of weight to be effected as compared with the quickest-running and lightest reciprocal engines. In the Turbinia extreme light- ness was attained, the total weight of machinery, boiler, shaft- ing, and propellers being 22 tons, for an estimated horse power of over 2,000--nearly 100 H. P. per ton of weight. This is about twice the power in proportion to weight as compared with a destroyer. This vessel had a boiler of special type, which was forced considerably, and. her runs at full power were of short duration; moreover, she had no reversing turbines for steaming astern. These features of the design sensibly reduced the weight. Other examples of the turbine system, however, fur- nish a fairer comparison with reciprocating engines, and make it certain that with a much slower rate of revolution than in the Turbinia, and with additional turbines for going astern at good speed, it is possible to effect considerable proportionate econ- omies of weight, or to increase speed. The destroyer Viper, with turbine machinery, was practically identical in dimensions with other destroyers having reciprocating engines, and she at- tained a maximum speed of about 36.6 knots on an hour's trial, and about 34 knots for three hours with the contract load on board. The latter speed is about 3 knots greater than the cor- responding speed on some of the best of similar destroyers with reciprocating engines, and 4 knots above the guaranteed speed of the latter. Messrs. Denny estimate that if the Clyde pass- enger steamer King Edward had been fitted with balanced twin triple-expansion engines df the best type instead of turbines, in association with the same boilers, the speed would have been reduced from 20.5 to 19.7 knots--corresponding to a difference of 20 per cent. in horse power. As one who, from the first in- troduction of the steam-turbine by Mr. Parsons in 1884, has been intimately acquainted with his work and with the difficulties he has overcome in the application of turbo-motors to various purposes, I would testify to the great courage and ability he has displayed throughout. In regard to the special application of turbo-motors to ship propulsion the difficulties have been great- est, and have only been surmounted by scientific and experi- mental work of the highest order. USE OF OIL MOTORS. "Another new departure now attracting much attention is the use of oil motors in launches and small swift vessels. In July last, after the Automobile. Club car races in Ireland, a con- test took place at Cork between oil motor launches, one of which is reported to have had an engine of 75 brake horse power, while others had 50 and 20 brake horse power. It is stated that a boat 30 ft. long, 5 ft. broad, and about 2 ft. deep, fitted with a 20-brake horse power oil motor, has been constructed by Messrs. Thorny- croft capable of attaining the remarkable speed of 18 knots, or nearly 21 miles per hour. The space occupied by this motor is not much larger than that required for a condensing engine of the same power, and the space required for boiler and coal was made available for accommodation. Gearing has been intro- duced: for reversing when required. It is interesting to compare these results with those obtained by the steam launch Miranda --also built by Thornycroft--on speed trials conducted by Sir Frederick Bramwell in 1872. This vessel was 45 ft. 6 in. long and 5 ft. 9 in. broad at the water line; on trial she carried 3 cwt. of coal, and had a displacement of 334 tons. She was fitted with a locomotive boiler and a two-cylinder vertical engine, cap- able of working at 600 revolutions, and developing about 72 H. P. (indicated). With 555 revolutions and nearly 60 I. H. P.-- probably about 50 brake horse power--gave the vessel a speed of 18.65 miles per hour. The machinery and boiler weighed about 2 tons, so that at maximum power--6oo revolutions--it developed about 36 I. H. P. per ton weight of propelling appa- ratus. It appears that the smaller oil motor launch attained a speed 214 miles greater than the Miranda, and the secret of her success laid in the fact that her propelling apparatus, with fuel for six hours, gave about 100 I. H. P. per ton. Obviously there should be the possibility of considerable developments in speed with such a motor as this. "Another interesting application of the oil motor is to the propulsion at the surface of submarine boats. Lieut. Dawson (of Messrs. Vickers, Sons, & Maxim) states that in the first submarine boats of the Holland type built by his firm, the four- cylinder gasolene engines give a maximum of 190 brake horse power, driving a single screw. The estimated speed at the sur- face was 8 knots, and the fuel carried is said to be sufficient for 50 hours at this speed (or 400 knots). When submerged, elec- tric motors are used. It is reported that the actual speed ob- tained on trial was 9 to 10 knots for the first boats; and that in [Jan. 7, later and larger vessels the oil motors have been much increased in power with a considerable increase in surface speed, If this is correct, it is probable that these vessels have the greatest power in oil motors yet applied to ship propulsion. DEVELOPMENT OF GAS ENGINES. "The progress made in recent years with gas engines of in- creasing power naturally raises the question whether they may not take the place of steam engines even in large ships. No one can fail to be attracted by the prospect of possibly dispensing with the use of steam as an intermediary, and directly using gas for internal-combustion engines. Of course, in sea-going ships questions of importance arise as to the power of covering long distances, and the arrangements for generating or storing gas, as well as obtaining adequate supplies of coal or oil. We are on the threshold of this subject; and it seems probable that a great deal more must be done on land in the development and use of gas engines of very much greater power than any yet constructed before the steam boiler disappears from ships. | Experiments of the character needed must not, and need not, be conducted on board ships. One thing is certain--naval architects and marine engineers will welcome and utilize any system which simplifies internal arrangements and minimizes weight and space. En- thusiasts dream of a time when gas turbines instead of recipro- cating engines shall be brought into use. Those more compe- tent to judge than myself appear disposed to think that very serious, if not insuperable, difficulties lie in the way of this sys- tem of utilizing power. However this may be, no initial steps seem to have been taken to practically realize the idea. SYSTEM OF TWIN SCREWS. "A notable feature in modern steamship construction is the largely-extended use of twin screws. This system was proposed in the earliest days of steam navigation, and it was adopted practically half a century ago on a small scale. Between 1860 arid 1865 a considerable number of twin-screw vessels were built, mostly vessels in which high speed was desired on moderate draught of water. Experience with the = last rigged ironclads (Alexandra and Temeraire) enabled me in 1878 to make an ex- tended analysis of their propulsive efficiency, and a comparison with that of a number of single-screw ships of recent construc- tion and deep draught. My conclusion was that, on the whole, the efficiency of the twin-screw ships was superior, which was contrary to the opinion generally entertained at that time. This opinion was not very favorably received at the time. Little was done towards adopting twin screws in mail steamers for eight or nine years. Then came the question of realizing 20 knots on the Atlantic service; and my friend, the late Mr. Thomas Imray, who had carefully studied my statements of 1878, consulted me when the design of the Teutonic and Majestic was- being pre- pared by Messrs. Harland & Wolff. Enlarged experience had only confirmed 'my conviction and emphasized by recommenda- tion of twin screws. They were adopted in the ships named, and in the two 20-knot ships built for the Inman Line about the same time--the City of Paris and City of New York. From that time it was certain that twin screws would take the place ~ of single screws for swift mail steamers. TRIPLE AND MULTIPLE SCREWS. "Triple and multiple shafts and screws have also been used for long periods in exceptional cases where shallowness of draught governed the dimensions of propellers. 'Cases in point are the floating batteries for river service, built during the civil war in America, with four shafts; the Russian circular ironclads, which had six shafts, and the Russian imperial yacht Livadia, which had three shafts. In recent years triple screws have been used in warships built in the United States, France, Germany, and Russia, but not in ships of the royal navy, except turbine- propelled vessels of small size. In the United States, after building, about ten years ago, two triple-screw ships of 19,000 H. P. to 20,000 H. P., which were reported to have done well, and, in face of the strong advocacy of the extension of the sys- tem by the engineer-in-chief (Admiral Melville), twin screws have been preferred for later battleships and cruisers up to 25,000 H. P. The Italians, after trials of triple screws in small ves- sels, have universally adopted twin screws. In France and Germany triple screws are generally adopted for battleships and cruisers, and in Russia a number of triple-screw cruisers have been built, but the great majority of ships have twin screws. Having been personally responsible for the continued use of twin screws in British ships up to 1902, it may not be out of place to put on record the reasons for that action, more especially as there have been repeated misrepresentations of the facts. by ill- informed persons, whose fundamental idea seems to be that foreign practice must necessarily be superior to British, and nothing but sheer obstinacy can account for a refusal to follow the lead of foreign designers. At first it was claimed that triple screws gave better propulsive efficiency than twin screws. Hav- ing had exceptional opportunities of making a thorough and ex- tended analysis of the actual performances of many ships, I have to state that this is not the case. The advantage in this respect is distinctly with twin screws so far; and although it is possible that, with larger experience, the performance of triple screws may be improved, and approach, or equal, that of twin screws, it is practically certain ,that, under existing limitations of draught, and with reciprocating engines making the number of revolutions and piston speeds now accepted, there is no reason why triple screws should be preferable to twin screws up to 40,000 H. P. There are many instances of distinct inferiority in triple-screw ships, and my foreign friends, who are building