Part 37 (1/2)
Heavy as Mr. Brunel's duties were in October 1854, when he wrote these words, a far greater amount of labour was subsequently imposed upon him.
During the year 1855 financial difficulties arose which interfered with the progress of the s.h.i.+p; and at last, in February 1856, although Mr.
Brunel had done everything in his power to prevent the necessity of such a step, the works were suspended; and they were not resumed till the end of May, after which date they were carried on by the Company under the supervision of the existing staff. It was greatly against Mr. Brunel's wishes that this was attempted, except as a temporary measure, as he considered it impossible for a company to carry on such a work efficiently and economically.
Notwithstanding all these difficulties, that which seemed at first only a confused ma.s.s of iron a.s.sumed by slow degrees the graceful proportions of a 'great s.h.i.+p'; and the hull of the vessel was completed by the end of the summer of 1857, so far as it was desirable to proceed before the commencement of the launching operations.
CHAPTER XII.
_STEAM NAVIGATION--THE 'GREAT EASTERN' STEAM-s.h.i.+P. THE LAUNCH._
A.D. 1857--1858. aeTATIS 52.
REASONS FOR DETERMINATION THAT THE s.h.i.+P SHOULD BE LAUNCHED BROADSIDE TO THE RIVER--AND THAT THE LAUNCH SHOULD BE SLOW--EXTRACTS FROM MR. BRUNEL'S REPORT OF FEBRUARY 1855--REASONS FOR THE ADOPTION OF IRON SLIDING-SURFACES--DESCRIPTION OF THE WAYS AND CRADLES--AND OF THE MOTIVE POWER PROVIDED FOR LAUNCHING THE s.h.i.+P--MEMORANDUM ON PROPOSED ARRANGEMENTS FOR THE LAUNCH (SEPTEMBER 26, 1857)--LETTER TO CAPTAIN HARRISON ON RIVER TACKLE (SEPTEMBER 30, 1857)--LETTER ON THE NATURE OF THE OPERATIONS (OCTOBER 23, 1857)--MEMORANDUM ON GENERAL ARRANGEMENTS AND INTENDED MODE OF PROCEEDING (OCTOBER 30, 1857)--HISTORY OF THE LAUNCH, NOVEMBER 3, 1857-JANUARY 31, 1858--LETTER TO THE DIRECTORS, NOVEMBER 26, 1857--REPORT AND MEMORANDUM ON THE LAUNCHING OPERATIONS (DECEMBER 17, 1857)--FLOATING THE s.h.i.+P--_NOTE A_: EXPERIMENTS AND OBSERVATIONS ON FRICTION.--_NOTE B_: LETTER TO W. FROUDE, ESQ.
(FEBRUARY 2, 1858).
The mode in which, the great s.h.i.+p was to be launched had necessarily to be determined before she was commenced. In May 1858, when the contract for her construction was entered into, the question was left open, and the contractor was either to launch her, or to build her in a dock 'if it be found preferable.' With Mr. Brunel's full concurrence, Mr. Russell determined to build the s.h.i.+p on the river-bank, broadside to the river.
The reasons which led to this determination were fully described by Mr.
Brunel in his report of February 5, 1855. This report has, with the exception of the parts relating to the launching operations, been printed above, p. 315. The pa.s.sages there omitted are as follows:--
One of the first points to be decided was the mode of launching the vessel, which of course would determine the position in which it was to be built; and I wish to take this opportunity of explaining my reason for adopting the plan I have decided upon, which, being unusual, might be supposed to be unnecessary.
Vessels are generally built above the level of high water, and then allowed to slide down an inclined plane into the water; occasionally, as in the case of the 'Great Britain,' they are built in a dry dock, into which the water is afterwards admitted, and they are floated out.
Both plans were well considered in the present case; but the size of the dock required, the difficulty of finding a proper site for such a dock, the depth required for floating a s.h.i.+p with her engines and boilers, which it was most desirable to introduce while building the hull, and the depth of channel required to communicate between such a dock and the deep water of the river, all combined to render the dock plan a very expensive, and, considering the nature of the soil in which it would have to be formed, a somewhat hazardous proceeding. Launching seems to offer the fewest difficulties and the greatest certainty; but the dimensions of the vessel required some modifications of the usual modes of proceeding.
Launching is generally effected by building the s.h.i.+p on an inclined plane, which experience has determined should be at an inclination of about 1 in 12, to 1 in 15, the keel of the s.h.i.+p being laid at that angle, and the head consequently raised above the stern, say one fifteenth of the whole length of the s.h.i.+p. In the present case this would have involved raising the fore part of the keel, or the fore-foot, about 40 feet in the air, and the forecastle would have been nearly 100 feet from the ground; the whole vessel would have been on an average 22 feet higher than if built on an even keel.
The inconvenience and cost of building at such a great height above ground may be easily imagined; but another difficulty presented itself which almost amounted to an impossibility, and which has been sensibly felt with the larger vessels. .h.i.therto launched, and will probably, ere long, prevent launching longitudinally vessels of great length. The angle required for the inclined plane to ensure the vessel moving by gravity being, say 1 in 14, or even if diminished by improved construction in ways to 1 in 25, is such that the end first immersed would become water-borne, or would require a very great depth of water before the forepart of the s.h.i.+p would even reach the water's edge. Vessels of 450 or 500 feet in length would be difficult to launch in the Thames unless kept as light as possible; but our s.h.i.+p could not be so launched, the heel of the sternpost being required to be, as I before said, about 40 feet below the level of the fore-foot. Some mitigation of the difficulty might be obtained by an improved construction of the ways; but the great length of ways to be carried out into the river would, under any circ.u.mstances, be a serious difficulty.
These considerations led me to examine into the practicability of launching or lowering the vessel sideways; and I found that such a mode would be attended with every advantage, and, so far as I can see, it involves no countervailing disadvantages. This plan has been accordingly determined upon, and the vessel is building parallel to the river, and in such a position as to admit of the easy construction of an inclined plane at the proper angle down to low-water mark.
In constructing the foundation of the floor on which the s.h.i.+p is being built, provision is made at two points to ensure sufficient strength to bear the whole weight of the s.h.i.+p when completed. At these two points, when the launching has to be effected, two cradles will be introduced, and the whole will probably be lowered down gradually to low-water mark; whence, on the ensuing tide, the vessel will be floated off. The operation may thus be performed as slowly as may be found convenient; or, if upon further consideration more rapid launching should be thought preferable, it may be adopted.
I have entered at some length into an explanation of all the reasons which led to the adoption of this plan; as I am anxious that they should be known, and particularly that it should be well understood by the proprietors and those interested in our success, that I am not adopting any novelties; unless, so far as those modifications of the more usual practices which experience points out as necessary to meet the peculiarities of a particular case may be deemed such.
I should add that the necessity, arising from the same causes, of launching transversely has been felt with long vessels of another description, namely, pontoons, or floating piers; one of 300 feet in length, which I have built at Plymouth, was so launched, and previously to this, one of 400 feet in length by Mr. Fowler on the Humber.[158]
I hope to be able to arrange that the machinery, which is to be provided by the contractor, for lowering the vessel down the ways will be also fitted to form a 'patent slip' arrangement for hauling the s.h.i.+p up for repairs; so that, if it should be found desirable to do so, such apparatus may be purchased for that purpose, and fitted up at the port which the s.h.i.+p will frequent. With the view of facilitating such an operation, or the grounding of the s.h.i.+p on a gridiron for examination at low water, a sufficient extent of the floor of the s.h.i.+p is formed perfectly flat, and is so strengthened as to allow the s.h.i.+p when loaded to be grounded without being unduly strained.
After it was determined that the s.h.i.+p should be built on the river-bank instead of in a dock, and parallel to the river instead of at right angles to it, the next point for consideration was, whether the s.h.i.+p should be lowered gradually to low-water mark, or whether a free launch should be attempted.
In a free launch the s.h.i.+p is allowed by the action of the force of gravity to run down the ways at a considerable velocity. In the case of the 'Great Eastern' there were insurmountable objections to this plan.