124 REPORT — 1839. 



MECHANICAL SCIENCE. 



On the most Economical Proportion of Power to Tonnage in Steam 

 Vessels. By J. Scott Russell, Esq. 



It is a subject of anxious inquiry with every proprietor and con- 

 structor of steam vessels, when about to construct a new steam vessel 

 for a given station, What is the best amount of power to place in my 

 ship, so as to accomplish in the highest degree economy, rapidity, and 

 regularity ? The inquiry is one accompanied with difficulties. If, on 

 the one hand, a large cargo is desired, which is generally the case, the 

 power of the engine is made small, for the purpose of occupying small 

 bulk, and consuming little coal; and although less velocity is then 

 acquired than with greater power, still less fuel is consumed with a 

 small engine than with a large one, and thus it is supposed that greater 

 economy is effected. This maxim, of a small proportion of power to 

 tonnage, is one on which many companies have long continued to act. 

 In other cases, where velocity is absolutely required, a much larger 

 proportion of power has been employed, and of course, by a large 

 power, there is a much greater consumption of fuel than by a small one 

 in a given time ; and not only so, but it is well known that this addi- 

 tional consumption is much greater than in the proportion of the 

 velocity gained; so much so, that a consumption of four times as 

 much I'uel will not give more than about double the velocity. Thus 

 it has appeared that the use of very great powers, and great expendi- 

 ture of fuel, has been made with only a very slight increase of velocity. 

 All this, the usual reasoning on the subject, goes to prove the value of 

 employing a small proportion of power to tonnage for economy. The 

 advantage of low powers and of low velocities, in point of economy, 

 would thus appear to be established ; but this apparent advantage in 

 theory has not been realized ; on the contrary, cases had been men- 

 tioned, at the Bristol meeting of the Association, in which it was 

 found, that by a gradual increase of power in the same vessel, while 

 the speed was increased, the consumption of fuel on the whole had 

 diminished. Mr. Russell, considering this subject worthy of further 

 examination, examined the books of the expenditure of fuel in the 

 steam vessels of several companies, and found that they were aware 

 that they had, on the whole, saved money by using high powers of 

 steam and high velocities, instead of low ones. This fact he had 

 examined carefully, and had arrived at a remarkable general result, 

 which appeared to him quite new, and to be of very great value 

 at the present moment, when such important interests were involved 

 in the successful extension of deep sea navigation. The general prin- 

 ciple at which Mr. Russell had arrived, was this: — That in a voyage 

 by a steam vessel in the open sea, exposed of course to adverse winds, 

 there is a certain high velocity and higher proportion of power, which may 

 be accomplished with less expenditure of fuel and of steam, than at a lower 



