ON FREIGHT AS AFFECTED BY DYNAMIC PROPERTIES. 93 



dynamic properties of mercantile steam-ships generally at the present time, 

 it might be regarded as invidious to refer to and particularize the actual per- 

 formances of vessels presentlj' employed on commercial service ; but it may 

 be affirmed generally that the ocean performance of mercantile steam-fleets 



does not average a coefficient of economic duty, by the formula ^ , 



exceeding 5600, whilst modern naval architecture and engineering have prac- 

 tically shown that with certain types of form the coefficient of performance 

 may be expected to vary fr^m 250 to 300, and that some engines of modern 

 construction have consumed only from 2 lbs. to 2| lbs. of coal per indicated 

 horse-power per hour, thus practically constituting a possible coefficient of 

 economic duty as high as 14,000, which has therefore been assigned to ship 

 A in the foregoing table, and whereby, under the conditions of the service 

 referred to, viz. ships of 5000 tons displacement steaming at 10 knots per 

 hour on a passage of 3000 miles, the conveyance of goods per ton weight 

 may be expected to be performed at fully 30 per cent, less cost than would 

 be necessarily incurred under the same circumstances by vessels of the same 

 size, but of which the coefficient of economic duty does not exceed 5600 ; and 

 this comparative difference would be greatly exceeded if the size of ships be 

 reduced, the length of passage increased, or the speed accelerated. 



From the foregoing statements it appears that public interests in the great 

 matter of Freight demand that steam-ships only of the most effective con- 

 struction, as respects hull and engines, be employed on mercantile service. 

 Bad types of hull and wasteful engines, necessarily, as we have seen, enhance 

 freight, increase the cost of production, and consequently curtail consumption, 

 thus constituting a blight on national industry. A check on these evils, 

 highly conducive to the gradual reduction of freight expenses by steam-ships, 

 would at once be instituted by making it a matter of contract slipula- 



tion that a definite coefficient of dynamic duty, by the formula • ^ 



should be realized on test trial of the ship, at the builder's load displacement 

 and steaming at the stipulated speed. Unquestionably, for years past, in our 

 popular marine engineering, prejudice and expediency have retarded pro- 

 gress ; marine engineering practice has not duly availed itself of the established 

 truths and science of the times : expansion, superheating, and surface con- 

 densation, now being reanimated as the basis of modern improvements, are 

 but the legacies of a bygone age hitherto neglected. 



It is only by directing public opinion to bear on such subjects of general 

 interest, that any prevalent evil can be corrected ; and surely an appeal on 

 the important subject of " freight," as affected by differences in the dynamic 

 properties of steam-ships, cannot be more appropriately made to any public 

 body than to the British Association, under the presidency of a man especially 

 distinguished and honoured in the path of practical science, and assembled 

 at Manchester, the birth-place of free trade, and the manufacturing capital 

 of the world. 



CHAS. ATHERTON, 

 Chief Engineer, H.M. Dockyard, Woolwich. 



