Economy of Fuel.-Knowing the consumption on board the Ericsson, the first step in a comparison to determine this point is to calculate the size and consumption of steam engines developing the same force. The working cylinder of a caloric engine, as now made, bears to that of a steam engine 1st. As being single instead of double acting, 2d. As having only of its area effective, owing to that of pressure, = 2 to 1 3 to 1 2.406 to 1 =14.436 to 1 A proportion equivalent to (2 x 3 x 2.406) Now, the Ericsson's working cylinder capacity consists of 4 of 168 inches by 6 feet, having a collective stroke displacement of 3696 cubic feet. Therefore, the steam cylinder must have 3696 14.436 -256 cubic feet capa city, which, cutting off at in two single strokes, gives 256 × 2 =170.67 × 60 × 101 revolutions=107522 cubic feet steam per hour, or (at 853= 107522 =126×6418106 pounds of 8106 water per hour, requiring a combustion of =1075 pounds per hr. (See page 42, last number of the Journal.) That of the Ericsson was 550 lbs., or 51 per cent. of the above. But upon the trials, the leakage of air is stated to have been great, owing to the action of the heat on the lower valves and seats, and to the unequal expansion of the working cylinder during the operation of the engine, its lower diameter having increased one-half inch more than the upper diameter; and as there was not enough elasticity in the piston springs to push out the packing, the leakage at the lower part of the stroke was considerable.† *The pressure above the supply piston commences at 0, and only arrives at 8 lbs, at of the up stroke, which is equivalent to cutting it off at 3; the working pressure is 8 lbs., which was cut off at 3-stroke. Hence, the working pressure effective was 8 lbs. acting during the stroke = 7·56 lbs. per square inch on the difference of areas of the working and supply pistons. To determine the leakage. Let the volume of the working cylinder be represented by as the air in the receiver was at a pressure of 8 lbs. the volume 1548 =0.434 V, at a pressure of 8 lbs.; 2 and if this were doubled in volume, (involving a heat of something like 493° Fahr.,) which is probably an extreme case, it could follow the piston so as to occupy a capacity of (0·434×2) V = 0.868 V, while it was actually cut off on the trial at V = .667 V. Hence we may take the whole leakage at (0.868 — 0.667) V On the presumption that the temperature to which the air was raised did not exceed that required to double its volume at 60°, this leakage might have amounted to 20 per cent. of the whole working cylinder, or •20 30 per cent. of that actually used. Should the whole of this be in 67 future overcome, either the pressure would be slightly increased with the same consumption, or the fuel would be reduced, the pressure remaining the same, in the proportion of 1.30 to 1.00, or from 550 to 423 pounds per hour-at which, in this comparison, it will be taken. This would be equal to nearly 40 per cent. of that of a steam engine. The difference between this amount of fuel (423) and the amount required by calculation (108) to raise the volume of 1,548,240 cubic feet= 120,920 pounds of air 30° the amount not to be returned by the regenerator, is enormous, being nearly 4 to 1; and it is probably owing in part to the radiation from the heated parts, and principally to the imperfect operation of the regenerator. As to the economy in working, we have no account of the amount of lubricating material to be used in warm cylinders, having nearly 1000 square feet of surface to be kept greased. Economy of Space.-We have now to consider the second advantage claimed, which is partially estimated on the reduction in amount of fuel for a transatlantic voyage, as occupying more room than that required by the new engine; and begin by a calculation of the power required to drive the Ericsson on the ocean at a speed equal to that of the Collins steamers. A few figures will show that to obtain this power in the Ericsson, her caloric engines would have to be increased to a size rendering the justice of this claim doubtful. The Collins steamers will make at the termination of a voyage (in New York harbor), 13 geographical = 15·55 statute miles per hour, with the steam pressure above taken, and making 17 turns per minute of a wheel 33 feet 3 inches effective diameter. At the same slip, the wheels of the Ericsson, making 103 revolutions of 303 feet effective diameter, should have driven her 8-873 miles per hour, which we shall allow as her actual speed. That this speed is inadequate for transatlantic navigation, will be readily seen from the following comparison. (Refer to page 42, present volume, for performance of the Arctic.) The mean of 12 passages between New York and Liverpool, gives as the distance 3080 geographical miles (of 60823 feet,)=3548 statute miles. At the rate of 63 miles per hour, this would require 524 hours-21 days 20 hours length of passage, which is not less than the average trips of the clipper ships. To obtain 15.55 miles with the Ericsson would require 183 revolutions per minute. Now the power required to drive a vessel is as the cube of the (15.55) speed-therefore, to make this latter speed would require (8.873) =5.375 times the power actually developed on the trial. Unless the working pressure were increased, which could not be done without augmenting the area of supply cylinders, and consequent back pressure; or the temperature which would destroy the cylinder bottoms with a rapidity in a far higher ratio than that of the increase of heat; or by cutting off shorter, (thereby slightly augmenting the initial pressure,) which would involve a higher per centage of leakage; the capacity of cylinder developed per minute must be increased 5.375 times, or would have to 3696 × 10 revs. x 5.375-11341 cubic feet, or with the same stroke, be 18.375 revs. = (6 feet,) 1890 square feet collective area, equal to four cylinders 24 feet 6 inches diameter, with supply cylinders 20 feet 2 inches diameter. The consumption of fuel would be 423 × 53-2279 pounds per hour =243 tons per diem. The same work could be done by two 90 inch X8 feet cylinders* with the above pressure and revolutions, and the consumption of fuel would be about 5000 pounds an hour = 60 tons a day. The coal saved in a trip of 12 days would therefore be 35 × 12 = 445 tons occupying 15,575 cubic feet. Now a pair of 90's x 8, oscillators, could be very readily put into an area of 30X15-450 sq. ft., which by the whole depth of ship is 450×22 and tubular boilers like those of the Golden Gate, with fire room between, into an area of 34×32×14 deep while the extra coal space required is Total, =10,125 cu. ft., = 15,232 Four caloric engines 24×6 feet would require an area of at least 115 feet in the length of the ship, and 30 feet in width, which by the whole depth (throwing off the projection above deck) 22 gives 115 × 30 × 221 =77625, or more than 13 times the space required for steam engines of equal power. Safety.-As regards safety, the chances would be decidedly in favor of the new plan. Experience, however, does not show that this advantage, or that of cheapness in passage, (owing to economy of fuel,) is properly appreciated when accompanied by reduced speed; and it is very doubtful whether engines of the size above named could, or would be put into a ship of the Ericsson's dimensions, in which case her speed would undoubtedly be too slow to ensure popularity. We have seen, then, 1st, That a saving of fuel of 60 per cent. may be effected. 2d, But that the space required would be 90 per cent. more than *The Steamer Georgia is 2483 feet long, 48 feet 8 inches beam, and has two 90 inch cylinders 8 feet, which with a less pressure than we have allowed above, drive the ship at about the same speed as that estimated for. that occupied by steam engines, boilers, and the saving of coal. In addition to which it must be recollected that in our comparison, the caloric engines were developing nearly their full power, while the steam engines were cutting off at one-third stroke; consequently, in heavy weather, a very slight increase of pressure on the pistons could be relied on in the former. The capability of following steam the whole stroke in a gale of wind ahead, is of material advantage to ocean steamers. As to river steamers, the difference of space and weight becomes even greater, as the amount of coal to be carried is trifling. We think the inference must be drawn from the foregoing, that unless some material change is made in the caloric engine as at present constructed, it is highly improbable that it will ever take the place of steam engines on fast steamers; and as regards freighting vessels, that clippers making average passages of 20 to 25 days across the Atlantic, will probably not be superseded by vessels in which so large a space is taken up by machinery and coal, of which the expenses of running and wear and tear cannot be insignificant, and whose passages will not be averaged in less time. This inference, however, it must be recollected, does not involve the failure of the object held in view in the construction of the Ericsson. That object we presume was to show that by certain peculiarities of construction introduced by Capt. Ericsson, into the engines hitherto used with air, their permanent or continuous operation might be secured, so that the mechanical difficulties (such as heavy losses from friction and leakage, rapid oxydation of metal, &c.,) which have hitherto prevented. that class of engines from extended use in practice, might be removed. That question cannot be decided in a few hours; it is the work of time with its usual experience, and if that experience shall show that the object above alluded to has been accomplished, it is not impossible that the Caloric Engine may be extensively employed in pumping or drainage, or in the many branches of manufacture where economy of fuel is the grand consideration, and there is no limit to the space or weight of the machinery to be employed. In view of these great manufacturing interests to which the benefits of Capt. Ericsson's invention would accrue, it is earnestly to be hoped that time will show the justice of his long continued confidence in his favorite project. M. For the Journal of the Franklin Institute. Notes on the United States Steamship Powhatan. Chief Engineer, U. S. Navy. (With a Plate.) By B. F. ISHERWOOD, The Powhatan is a very similar steamship to the Susquehanna, an account of whose performance is given in the last October number of this Journal. The return of the Powhatan from her first few months' cruising, afforded me the opportunity of obtaining her exact performance from the steam log, which I have tabulated for brevity, and in which I have given separately the means for each number of consecutive hours, where the weather, sail, cut-off, &c., remained unchanged. This table contains all the steaming done. The engines of the Powhatan and Susquehanna, are of the same type, inclined and direct acting; they have cylinders of the same diameter and stroke of piston, and differ from each other in details only. They both cut off by the steam valves, which are of the double puppet kind; Sickels' arrangement for cutting off being used in the Powhatan, and Stevens' in the Susquehanna. The hulls of the Powhatan and Susquehanna, though of the same linear dimensions, have very different water lines. The bow of the Powhatan is much sharper than the Susquehanna's, while the stern of the latter ship is much finer. The two ends, or rather the fore and after body of the Powhatan, are exactly alike, the dead flat being at the centre of the water line, while the model of the Susquehanna more nearly resembles that of a sailing vessel, with bow fuller than stern, and dead flat placed forward of the centre of the water line. Both vessels are sparred alike and spread equal amounts of canvass, viz: 21,230 square feet. Displacements and Areas of Immersed Amidship Sections at the following drafts of At 18 feet 6 inches draft of water, the centre of displacement below water line is 8.86 feet; and the height of the metacentre above the centre of gravity of displacement is 10.87 feet. The position of the centre of displacement is, as has been before stated, exactly at the centre of the water line. By a comparison of the above with the corresponding items of the Susquehanna's hull, it will be seen that at 17 feet 6 inches draft from bot |