Mercantile Steam Transport Economy as affected by the Consumption of Coals. By CHARLES ATHERTON, Chief Engineer, Royal Dockyard, Woolwich. PUBLIC usefulness, as dependent upon science, being the great object for which the "British Association for the Advancement of Science was originated, and has now been signally upheld for twenty-nine years, a period remarkable for the progress that has been made in the utilization of the powers of nature, to such an extent that the international condition of the globe is now being revolutionized by the progressive practical utilization of elements which heretofore were regarded merely as phenomena of nature, viz. Steam and Electricity; in which revolution the application of steam to the purposes of navigation has played so conspicuous a part, that now, in proportion as steam may be effectively employed in the pursuits of commerce and of war, it is acknowledged that even nations will rise or fall; seeing, moreover, that at no period in the history of steam navigation has so great a step been made in its practical development as has recently been realized by the fearless introduction, in marine engineering, of the long known but neglected effects of increased pressure, superheating, and expansion; the recognition and application of which principles have now, at length, been attended with such effect in marine engineering, that the consumption of fuel with reference to power is now known to be practically reducible to less than one-half of the ordinary consumption of coal on board ship;-seeing also that mercantile enterprise, setting no limit to speculative investment, has in these days emancipated mechanical intellect from the restrictions by which ideas as respects magnitude have hitherto been bound ;-under such circumstances I cannot doubt that any effort to popularise a knowledge of the practical utilization of steam, with reference to the consumption of fuel, though advanced with no pretensions to science, beyond that which may be awarded to originality and labour in the application of calculations to develope useful results, will be favourably received, more especially as the paper which I now beg to present is in continuation and conclusion of an inquiry, which has already, in part, on two occasions been favourably entertained by this Association, and honoured with a place in its published records. The former papers to which I allude are,-1st," Mercantile Steam Transport Economy, with reference to Speed," vol. for 1856, p. 423; 2nd, "Mercantile Steam Transport Economy, with reference to the Magnitude of Ships, and their Proportions of Build,” vol. for 1857, p. 112. And I now purpose to bring this inquiry to its conclusion by the following paper on Mercantile Steam Transport Economy, as affected by the Consumption of Coals. My purpose, and the drift of my remarks will probably be the more readily understood by my at once adducing the following Tables C and D, and the diagram E, in continuation of the Tables A and B, which are published in the Volume of Reports for the year 1857, pp. 116 and 119, observing with reference to these Tables C and D, that the rate of consumption of coal on which the calculations are based, viz. 24 lbs. per indicated horse-power per hour, has been practically realized on continuous sea service, although the ordinary consumption of steam-ships in the Royal Navy, as well as in the best vessels of the most celebrated steam-shipping companies, is, I believe, at the present time fully 50 per cent. in excess of that amount; and I may say, that in steam shipping generally, the consumption of coals per knot of distance, with respect to displacement and speed, is double the consumption which these Tables, based as they are on an example of existing practice, show to be now practically realizable. TABLE C. Calculated for the Speed of 10 knots per hour. The Tables now adduced are as follow: TABLE C.-Calculated for the Speed of 10 knots per hour, and showing the mutual relations of Displacement, Power, and the Consumption of Coal, per Day, Hour, and Knot, the Coefficients of Dynamic performance, deduced V3 Di Ind. h. p.' from the Formula being assumed to be 250, and the consumption lbs. per Ind. h. p. per hour. deduced from the Formula 10, 15, 20, and 25 Knots per Hour:-the Coefficient of Dynamic Performance Coals consumed per Day, per Hour, and per Knot, for the respective Speeds of TABLE D.-Showing the Mutual Relations of Displacement, Power, and Ind. h. p. sumption of Coals at the rate of 24 lbs. per indicated horse-power per hour. being assumed to be 250, and the Con Coals, in Cwts. per Knot. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 DIAGRAM E, showing approximately the Nautical Mileage Consumption of Fuel, for vessels from 1000 tons displacement, up to 25,000 tons, the CoV3 D efficients of Dynamic Performance deduced from the Formula Ind. h. p. being assumed to be 250, and the Consumption of Coals being assumed to be at the rate of 2 lbs. per Ind. h. p. per hour. 20 25 26 With reference to the foregoing Table C, showing the mutual relations of displacement, power, and the consumption of coals per day, per hour, and per knot, for vessels of a gradation of sizes, from 250 tons displacement up to 25,000 tons, the coefficient of dynamic performance, deduced from the formula V3 DI being assumed to be 250, and the consumption of coals being assumed Ind. h. p. to be at the rate of 24 lbs. per indicated h. p. per hour, on these data, the coefficient of dynamic economy with reference to coals deduced from the formula V3 DI w (w being the consumption of coals per hour expressed in cwts.) becomes 11210. It will be observed that in Table C the tabulated sizes of ships, as determined by their respective load displacements, increase progressively from 250 tons displacement up to 25,000 tons, showing under assumed conditions, which, however, are justified by now realized advancement in ship and engine construction, the mutual relations of displacement and coals calculated for the speed of 10 knots per hour as most convenient for a standard of reference. The intended practical use of this Table C is to facilitate mercantile investigation into the dynamic merits of steam-ships as locomotive implements of burden by comparing their actual consumption of fuel with the calculated consumption of the ship of corresponding size and speed as recorded in this tabulated standard of comparison, whence the constructive merit of ships, as respects their working economy of fuel, on which the cost of freight so much depends, may be relatively ascertained. For example, a certain ship of 800 tons mean displacement attains the speed of 8.8 knots per hour, with a consumption of coals certainly not exceeding 4-3 cwt. per hour, or 49 cwt. per nautical mile or knot; which (as the consumption of coals per knot varies cæteris paribus as the square of the speed) is equivalent to '63 cwt. per knot at the speed of 10 knots per hour. Now by referring to Table C, we find that on the assumed data therein referred to, the standard ship of 800 tons displacement, steaming at 10 knots per hour, would consume 77 cwt. of coal per knot. Hence, therefore, it appears that the ship referred to in this instance is superior to the tabulated standard in the proportion of ⚫77 to 63, that is, in the proportion of 122 to 100, the superiority with reference to the consumption of coals per knot being 22 per cent. Again, a certain ship of 3500 tons mean sea displacement makes a voyage at the average speed of 12.88 knots per hour, consuming 83 cwt. of coal per hour, or 644 cwt. per knot, which, by the law of dynamics above quoted, is equivalent to 3.88 cwt. per knot at the speed of 10 knots per hour; but by referring to the Table of comparison C, we find that the standard ship of 3500 tons displacement, steaming at 10 knots per hour, would consume only 2.06 cwt. of coal per knot. Hence, therefore, it appears that the ship referred to in this instance is inferior to the tabulated standard ship in the proportion of 2-06 to 3.88, that is, in the proportion of 53 to 100, the inferiority with reference to the consumption of coals being 47 per cent. Thus, by reference to this tabulated standard of comparison (C), we have the means of readily deducing the exact per-centage by which ships, as respects the dynamic duty performed with reference to the consumption of coals, differ from each other. I need not dwell on the importance of this consideration as affecting the commercial value of ships for sale or charter. With reference to Table D, showing the mutual relations of displacement, power, and coals consumed per day, per hour, and per knot for the respective speeds of 10, 15, 20, and 25 knots per hour, the object of this Table is to show the extent to which the required engine-power, and the nautical mileage consumption of coals are dependent on the rate of speed, thereby facilitating the adaptation of ships as respects their size and power to the service that may be required of them. For example, by referring to Table D, we observe that a ship of 5000 tons displacement, steaming at 10 knots per hour, requires 1170 indicated h. p., and consumes 261 cwt. of coal per knot; but to steam 15 knots per hour, the same vessel would require 3947 ind. h. p., and the consumption of coals |