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136 THE Marine REVIEW April, 19j9 The Effect of Superheat on the Economy of a Marine Engine as Determined by Tests on the Steam Yacht Idalia By Lieut. JoHN HALLIGAN Jr; Uz S. N., MEMBER. N Oct 11) 12,15 and. 14 1909. comparative tests were made of the steam consumption of the main engine, feed, circulat- ing and air pumps of the 'steam yacht Idalia, using saturated steam and steam with from 5/7 degrees to 105 degrees Fahr. superheat. These tests were conducted by Dr. D. S. Jacobus, under the direction of W. D. - . Hoxie, the owner of the Italia, through whose courtesy tests 3, 4 and 5 were (independent), 6x12x8 in. Circulating pump (centrifugal), 5 7/16x5 in. Under ordinary conditions of cruising, about 100 degrees of superheat is car- ried. Except in the case of the dynamo engine, all of the auxiliaries take super- heated steam at full boiler pressure. The only lubricant used in the main and auxiliary steam cylinders is fine graph- ite mixed with water. On the main en- gine, this mixture is introduced by means of a hand-lubricating pump fitted at the throttle, which stipplies all the lubricant required for the four main SHETCH OF WEIGHING TANKS ETC. 10 STEAM YACHT /DALIA SCALE Yy"= 1 Fr. Wov. 3-/909 CONDENSER ed on platform scales, from which it was discharged into a feed tank. Tem- peratures and pressures were recorded at intervals of 15 minutes. Frequent sets of indicator cards were taken, the results of all of which are shown in the tables. New indicators with outside springs were used. The gross and tare weights of each tank full of water were measured and the net weight of the partially filled tank at the end of each hour was recorded. The dynamo engine was not run dur- ing the tests. The only other auxiliaries BABCOCKBIVILECOX MARINE BOILER FIRE RO0N | Q . STEAM PIPE » THENSROME: FOR svi eae *7 LZ orwAamo EX) <S WEIGHING Np ! + Ano SUPERHEATER PLAN VIEW witnessed by the writer, representing the bureau of steam engineering. The Idalia is of the following general dimensions: Length over all, 178 ft: length of waterline, 140 ft.; beam, 20 it.;; depth, 10 ft.;.draught, 9 ft.; gross tonnage, 201; net tonnage, 111. She is propelled by a four-cylinder, triple-expansion engine, 1114, 19, 22 11/16 and 22 11/16 by 18 in. 'stroke, the valves of which are all of the piston type. Steam is supplied by a Babcock & Wilcox boiler, burning anthracite coal, with 65 sq. ft. grate surface and' 2,500 sq. ft. heating surface. A superheater of 340 sq. ft. heating surface is fitted, as shown in Figs. 2 and 3. The auxiliaries connected with the tests are of the following dimensions: Feed pump; 6x4x6 in. Air pump *Reprint from ¢ the Journal of the American Society of Naval Engineers. Fic. I pistons and their respective valves. No difficulty has been experienced in the upkeep of the plant attributable to the use of superheated steam. That the cylinders are in excellent condition is evidenced by the efficiency of the engine, as shown on the tests. The tests consisted of runs under con- ditions that were practically identical as regards their effect on the results, The main engines and auxiliaries were run at nearly constant speeds. The same indicators, thermometers and gages were used in all the tests, so that the results are strictly comparable. The steam used by the main engine, the feed, the air and the circulating pumps (all of which are independent) was determined by weighing the cons densed steam discharged from the sur- face condenser, it being pumped from the hot-well into a weighing tank mount- STEAM To SUPERMEATER --the blower engines--exhausted into the atmosphere. : No attempt was made to record coal consumption or other boiler data, as the tests were too short to. afford accurate data of this sort. The tests were, however, of sufficient duration to give an accurate determina- : tion of steam consumption, as 1s evi- denced by the uniformity of the hourly data. The result for any hour of the tests plots very. close to the curve shown in Fic, 5, The superheater shown in Figs. 2 and 3 was designed to provide 100 degrees of superheat; this established the upper limit of the tests. The lower degrees of superheat were obtained by mixing superheated with saturated steam, and by partly shielding the superheater from the hot gases by means of asbestos mill board. It was impossible with the means