ON MERCANTILE STEAM TRANSPORT ECONOMY. 129 



would be 5-87 cwt. per knot ; hence it appears that to increase the speed 

 from 10 to 15 knots per hour, the power requires to be increased upwards 

 of three times, and the consumption of coals per knot is more than doubled. 

 Again, let it be supposed that the weight of the hull of a ship of 5000 tons 

 displacement fitted for sea amounts to 40 per cent, of the displacement, or 

 2000 tons, and suppose the weight of the engines and boilers to be one ton 

 for each 10 indicated h. p., the vessel requiring, as shown by Table D, 1 170, 

 indicated h. p. to attain the speed of 10 knots per hour, with a consumption 

 of coals at the rate of 2'61 cwt. per knot; then on these data, the engines, 

 to attain the speed of 10 knots per hour, would weigh 1 17 tons, and the weight 

 of coals for a passage of, say 12,000 nautical miles, would be 12,000 X 261 = 

 31,320 cwt., or 1566 tons weight, making together for hull, engines and 

 coals 2000+117 + 1566=3683, and consequently the displacement avail- 

 able for cargo would be 5000—3683 = 1317 tons weight. But if it be 

 purposed that the steaming speed shall be at the rate of 15 knots per hour, 

 the required power, as appears by Table D, will be 3947 ind. h. p., con- 

 sequently the weight of the engines will be 395 tons, and the maximum dis- 

 placement available for coals will be 5000—2395 = 2605 tons weight, or 

 52,100 cwt, which, at the tabulated rate of consumption, 5*87 cwt. per knot, 

 would be sufficient only for a passage of 8876 nautical miles, and this to the 

 utter exclusion of all goods cargo, showing that the ship is inadequate for 

 steaming 12,000 nautical miles at the required speed of 15 knots per hour, 

 though the same ship, if duly fitted with engine-power for steaming at 10 

 knots per hour, would perform the whole passage of 12,000 nautical miles 

 without re-coaling at any intermediate station, and carry 1317 tons of re- 

 munerating goods cargo. 



These few examples will, it is hoped, sufficiently illustrate the application 

 and use of Tables C and D in facilitating mercantile inquiry into the capa- 

 bilities of steam-ships with reference to the all-important question of con- 

 sumption of coals ; but in order still further to facilitate calculations on this 

 subject, the diagram E has been prepared, whence, simply by inspection, the 

 consumption of coals per knot, at any rate of speed, may be approximately 

 ascertained for vessels of improved modern construction up to 25,000 tons, 

 the data on which this diagram has been calculated being the same as that on 

 which Tables C and D are based. 



The use and application of this Diagram E is evident ; it brings theTables 

 under ocular review, and generalizes their application. It is given as an 

 example of a system that admits of being more fully and elaborately deve- 

 loped for the purposes of mercantile tabular reference, as is now being done 

 for publication. 



Having thus explained the use and application of Tables C and D and the 

 Diagram E, it will be perceived that the task which I have undertaken on this 

 occasion is to show palpably by comparison with these tabular statements, based 

 on data ivithin the limits of already realized results, taken as a standard, what is 

 the relative character of steam-ships as respects their locomotive or dynamic 

 capabilities, with reference to the economic performance of mercantile trans- 

 portservice, so far as dependent on the consumption of fuel ; thus affording 

 an exposition whereby parties interested in steam-shipping, either as owners 

 or directors, or agents, or as the charterers of shipping for government or for 

 private service, though unacquainted with the details of marine engineering 

 as a science, may be enabled to arrive at some definite appreciation of the 

 capabilities that may be expected of steamers ; that is, the weight of cargo 

 they will carry, and the length of passage capable of being performed at any 

 definite speed; for, as before observed, the dead weight of cargo that a ship 

 1859. k 



