Part 26 (2/2)
Marine engines of 80 or 90, and even some of 100 horse-power, are mere models on a large scale of the ordinary-sized engines. Engines of 160 or 180 horse-power each would be unmanageable without many material modifications in the details; the arrangement must be different, and, as the strength of materials remains the same, the proportionate dimensions of the parts must be modified. Many contrivances of this description have been introduced into the large engines of 110 horse-power each made for the Navy. From 110 to 160 is still another and a very great stride. Those who have led the way in the first step are certainly the most likely to be aware of the difficulties of the second, and to be able to appreciate them better, and be more prepared to overcome them than those who have as yet only manufactured, however successfully, engines of the ordinary cla.s.s. Of three parties tendering.... Messrs. Maudslay have made by far the largest number, and have for some years led the way in the introduction of the largest armed steamboats; and there can be no question as to the fact that they are the oldest manufacturers of marine engines, that they are themselves the originators of the greatest number of the improvements of the day, that they have made the largest engines yet made, and the greatest number of large engines of all sizes; and, lastly, that they have the princ.i.p.al supply of engines for the large war s.h.i.+ps now used for the Navy, and have had hitherto the sole supply of all above 70 horse-power. With these facts before you, it remains only for you to consider how far you agree with me in the conclusion I have come to, and which I have no hesitation in expressing--that I think you will be safest, in the peculiar case of the first s.h.i.+p, in the hands of the parties who have had most experience, and that Messrs.
Maudslay are those persons. Their price is, I think, moderate.
This report was read by Mr. Brunel at a meeting of the Board, summoned at his request; the Directors adopted his advice, and accepted the offer of Messrs. Maudslay & Field, of Lambeth.[119]
The 'Great Western,' for so the s.h.i.+p was called, had not been long commenced when a somewhat celebrated controversy arose, in which the correctness of Mr. Brunel's views was questioned by the late Dr.
Dionysius Lardner.
The circ.u.mstances which led to this discussion were as follows:--
The British a.s.sociation for the Advancement of Science held its sixth meeting at Bristol in August 1836; and, as Dr. Lardner was announced to lecture on Transatlantic Steam Navigation, great interest was felt in Bristol on the occasion.
After some postponement, he delivered his lecture on August 25, to a crowded meeting of the Mechanical Section. The proceedings of the a.s.sociation unfortunately do not give any report of Dr. Lardner's observations; but, as in his latest work on the subject[120] he speaks in commendatory terms of the report given in the 'Times' newspaper, that account may be relied on as correct.
In the 'Times' of August 27, 1836, it is stated that in the course of his lecture Dr. Lardner said,--
Let them take a vessel of 1,600 tons, provided with 400 horse-power engines. They must take 2? tons for each horse-power, the vessel must have 1,348 tons of coal, and to that add 400 tons, and the vessel must carry a burden of 1,748 tons. He thought it would be a waste of time, under all the circ.u.mstances, to say much more to convince them of the inexpediency of attempting a direct voyage to New York, for in this case 2,080 miles was the longest run a steamer could encounter: at the end of that distance she would require a relay of coals.
There is no detailed report remaining of the animated discussion which followed the lecture, and in which Mr. Brunel took part. He exposed several errors in Dr. Lardner's calculations, but failed to produce any effect upon the majority of those present, who were powerfully impressed by the lecturer's dogmatic a.s.sertions.
Those a.s.sertions seem to have had a wide circulation beyond the walls of the lecture-room; and if Dr. Lardner's arguments were sound, and if transatlantic steamers ought to have taken their departure from 'the most western sh.o.r.e of the British Isles,' the enthusiastic advocate of a railway scheme in Ireland might well exclaim,--
The promoters of this vast object stand forewarned of defeat. Dr.
Lardner, who has bestowed a great deal of pains in arguing the bearings of this undertaking, has p.r.o.nounced it impracticable; and I entirely agree with him in his conclusions. The effort, nevertheless, will be made; the genius of English enterprise will hazard the consequences; and every honest spirit that shall hear of the brave British crew which will embark upon that perilous expedition will feel his heart beating high for the merchant-sailor, whom nothing can deter. He will sail; but, though dangers will encompa.s.s him, and destruction appear, there is yet a hope for his ultimate success. Let us cheer ourselves with the expectation that, as the exhausted mariner returns, he will fall in with the western sh.o.r.es of Ireland; that, worn out and hopeless of home and comfort upon earth, the Shannon will win him to her bosom; that, invited by the graceful sinuosities of that n.o.ble stream, and the rich and fertile lands around, he will advance to this convenient and improving city; and as he rests within its walls that he will exclaim, 'This is the place from which I ought to have set out, for here have I returned with ease and safety!'[121]
Dr. Lardner's views are repeated in an article in the 'Edinburgh Review'
for April 1837 (vol. lxv.); and in the report of the proceedings of the British a.s.sociation for 1836 (p. 130 of the proceedings of the sections), the reader is referred to this article, apparently as a subst.i.tute for an abstract of the lecture.
The following _resume_ is there given of the lecture:--
The conclusions at which he arrived were briefly these: that, in the present state of the steam-engine as applied to nautical purposes, he regarded a permanent and profitable communication between Great Britain and New York by steam-vessels making the voyage _in one trip_ as in a high degree improbable; that since the length of the voyage exceeds the present limits of steam-power, it would be advisable to resolve it into the shortest practicable stages; and that, therefore, the most eligible point of departure would be the most western sh.o.r.es of the British Isles, and the first point of arrival the most eastern available parts of the western continent; and that, under such circ.u.mstances, the length of the trip, though it would come fully up to the present limit of this application of steam-power, would, nevertheless, not exceed it, and that we might reasonably look for such a degree of improvement in the efficiency of marine engines as would render such an enterprise permanent and profitable. (P. 119.)
Among other objections to long voyages the reviewer enumerates the incrustation of boilers, and the choking of smoke flues; and then, with reference to the quant.i.ty of fuel required, he proceeds:--
In proportion as the capacity of the vessel is increased, in the same ratio or nearly so must the mechanical power of the engines be enlarged, and the consumption of fuel augmented.... It is therefore demonstrable that, in the present state of steam navigation, if this voyage shall be accomplished in one uninterrupted trip, the vessel which performs it must, whatever may be her power and tonnage, be capable of extracting from coals a greater mechanical virtue, in the proportion of three to two, than can be obtained from them by the combined nautical and mechanical skill of Mr.
Lang, the builder of the 'Medea,' and Messrs. Maudslay and Field.... That the pa.s.sage from Liverpool to New York cannot on any occasion be made in one run by a steam-s.h.i.+p we do not maintain....
The average time of the outward voyage to New York is thirty-six days, and we say that when the circ.u.mstances of wind and water are such that a sailing vessel would require that time to make the pa.s.sage, a steamer cannot make it without an intermediate supply of fuel. (Pp. 127, 139, 143.)
To sum up Dr. Lardner's views in his own words written at about this time,[122] 'We have as an extreme limit of a steamer's practicable voyage, without receiving a relay of coals, a run of about 2,000 miles.'[123]
It will be seen from these extracts that the proposition Dr. Lardner laid down as the basis of his 'demonstration' was, that the power of the engines must be increased as the size of the vessel. Were this true his conclusion would also be true--namely, that the capacity of a given vessel regularly to accomplish a given voyage does not increase with the increase of size, since the consumption of fuel is augmented in about the same ratio.
This a.s.sumption is directly opposed to the opinion held by Mr. Brunel, and acted on by him in his recommendations to the Steam-s.h.i.+p Company--namely, that while the tonnage of a s.h.i.+p is increased as the cube of her dimensions, the resistance is increased only about as the square.
This question was the main point at issue between Dr. Lardner and Mr.
Brunel; and the proposition which Mr. Brunel then a.s.serted is at the present time the basis of the calculations which determine the proportion between the tonnage of a steam-s.h.i.+p and the length of voyage she has to perform without a relay of fuel.
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