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328 af propeller working at from 70 to 120 revolutions. For an account of the proposals as put forward, a study of the papers on -electric power for mam marine propul- sion, brought before the Institution of Engineers and Shipbuilders in Scotland by Mr. Mavor, and later before the Institute of Marine Engineers, London, by Mr. Durtnall, wil be found inter- esting. Should this system of main electric drive for working screw-propel- lers direct come about, it may be safely said that a new era of eiectric naviga- tion is about to dawn, and one promis- ing great results. For instance, the continued decrease in the _ boiler-pres- sures as commenced with the steam- turbine machinery will no doubt be further continued, and even lower pres- sures than now exist will be made use of, which will largely decrease the weight of boiler instaations and so cheapen the first cost.. Through the fact of the greater portion of the ma- chinery being electrical other than mechanical, the heavy weights of such moving parts as pistons, piston- and connecting-rods, slide-valves, link mo- tion, eccentrics, etc., will be done away with, and so render the outfit and overhauling of the electric boat (a ves- sel propelled by electricity generated on board by steam) more simple and more easily effected than on the steam-pro- _pelled. craft. at present in use. Looking back to the papers previously read on this subject, it wil be seen that no such remarkable changes have taken place since the mtrcduction of steam navigation as during the few years which have passed since the com- mencement of the present century. In none of the previous papers has even an allusion been made to the likely 'use of the internal-combustion engine or the suction-gas for marine propul- sion, and only in the last paper read by Mr. McKechnie in 1901 was mention made of the Parsons turbine, which is the first successful adoption of rotary instead of reciprocating or piston ma- chinery. results attained to 'date, they Coming finally to the by marine engineering may be summarized as follows: Ves- sels of close upon 800 ft. length and over 38,000 tons displacement are being propeled across the Atlantic at an av- erage speed of 2514 knots, by. turbine machinery working up to about 70,000 'Wo Py) having 4 consumption of up- wards of 1,000 tons per day. Similar results have been given in the turbine- propelled warship "Indomitable" of over 40,000 I. H. P., and maintained across the Atlantic with water tube boilers. So far as the merchant marine is THe MARINE REVIEW concerned, there is at present no sign that the great horsepower of the "Lusi- tania" and "Mauretania" will be : ex- ceeded or even equalled ior some years to come, as the large vessels now under construction for the White Star Line, following the types of the vessels con- structed by them during the past 20 oyears; are reported to have but a mod- erate speed of about 20 knots, so that the machinery installations will be on_y of very moderate dimensions and power. This latter course is also being followed by the continental lines, all their more recent vessels not exceeding 18 knots, SIR JOHN THORNYCROFT'S SKIMMER, MIRANDA III. This unique vessel is a mahogany boat, 22 ft. long, which under normal conditions seems to be a river launch, September, 1909 tion, the whole of the keel being quite above the water. A little spray is thrown up, but hardly any wave or wash is created. When the boat is utilized as an ordinary launch, travel- ing in submerged state, the speed js seven to eight knots, with: the motor making about 500 revolutions, but when these are increased to 1,450 revolutions, the vessel darts forward into the skimming position, and the speed is accelerated at a greater rate until from 23 to 27 knots is attained. The boat is steady at high speeds, but a quick see-saw motion is noticeable in choppy water, doubtless owing to the extraordinary position the center of gravity must be in. The speed ob- tained from such a short, broad hull, is simply marvelous and could not be obtained from a normal type of vessel. The engine is of the Thorny- Sir JOHN THORNYCROFT'S SKIMMER but is adapted for skimming on. the surface when propelled at high speed. This boat, while normally seven knots speed, can attain a speed of 27 knots in smooth water, the increase in pow- er being enormously less than is usually the case, even for suitably- designed hulls immersed under ordi- hary conditions. Her beam is 6. it. lin, and depth 2 it; 9 in. The bot- tom of the boat is shaped like a flat fish; the upper part is a whaleback. Under the keel forward a vertical fin plate is fitted, having a horizontal plane fitted at right angles to the fin. When going ahead as the boat in- creases in speed, the stern droops and the bow rises. At about 20 miles an hour, the horizontal plane reaches the surface of the water, and the boat skims, or glides, being supported only by the plane and the s.ern, which is of peculiar form to meet this condi- Mrranpa III. croft motor car type, fitted amidships with slight modifications to suit ma- rine practice. Thus the valves are On the top, and the pumps at the forward end, so as to be thoroughly accessi- ble. There are four cylinders of 4-in. Dore. "The engine drives a_ three- bladed propeller 16% in. in diameter, the engine and shaft being set at an angle so that the propeller is at a considerable distance below, as_ well as projecting beyond the stern post. On trial, with a weight correspond- ing to one ton displacement, this boat averaged 27 knots during six runs over a measured course in fairly smooth water, the power of the machinery being estimated at 58 B. H. P., where- as in normal trim the speed is but It will be seen that a great increase in speed is got seven or eight knots. when skimming for a relatively small Increase in power.