These tenders do not include, in the case of the engines, either the screw itself or the paddle wheels, nor, in the case of the vessel, the cabin fittings, masts, and rigging, boats, or stores. I should estimate these roughly at 50,000l. more,—at least such an allowance ought to be ample; but these details will require a great deal of consideration, and could not be included in the original contracts; while at the same time they can mostly be better and more economically supplied by competition or by arrangement with the special makers of the respective articles....
During the next six months Mr. Brunel was engaged in preparing the formal contracts and specifications. These documents were settled with much care, and after frequent communications with the contractors, who consented to the insertion of clauses which gave the full control and supervision over every part of the work to the Engineer, with very large powers of interpretation. They required, however, that, should Mr. Brunel cease to act as Engineer, any disputed point should be settled by arbitration, and not by his successor.
Besides the delay occasioned by the magnitude and novelty of the undertaking, there were other difficulties which helped to postpone the commencement of the works. The Directors were unable, under their charter, to enter into any contracts until a certain amount of their capital was actually paid up; and, as several shareholders had retired when the change of plans was determined upon, it was no easy work to get the shares taken. That this was eventually accomplished was due mainly to the exertions of Mr. Brunel and Mr. Charles Geach, one of the Directors.[146] ‘Could I have foreseen,’ Mr. Brunel writes, ‘the work I have had to go through, I would never have entered upon it; but I never flinch when I have once begun, and do it we will.’
Several times they nearly broke down, but at length the contracts were signed, and on the same day, December 22, Mr. Brunel gave the formal notice to the contractors to proceed with the works. ‘After two years’ exertions (he wrote), ‘we are set going, the contracts entered into, and the work commenced.’
Extracts from Mr. Brunel’s Memoranda, A.D. 1852-1853.
July 11, 1852.—The dimensions I commenced with in March last, of 650 × 70 × 30 appear after all to be not far wrong, according to present views. I make them now 700 × 70 × 24 about; but much depends upon the last dimension, the draught. If another foot or two can be safely taken it will be of great advantage.... With this size of vessel, having a midship section of about 1,800, and a length of 700, I assume a nominal horse-power of about 2,500. The first question of importance is, in what proportion shall this be divided between the screw and paddles?... My present impression is to halve the power between the two.
In both the engines every known means must be adopted to secure efficiency:—1, An excess of boiler power; 2, expansion permanently, say at ⅓; 3, steam of not less pressure than 20 lbs., and I should prefer 25 lbs.; 4, that cylinders, particularly top and bottom, slide chest, and steam pipes, be all jacketed, and the jacket supplied with steam from an auxiliary boiler of at least 10 lbs. more pressure than that of main boilers; and it would be very desirable to make some experiments to determine whether it is not worth having a heating apparatus to heat the steam immediately before it enters the cylinders.[147]
July 17.—After a long conference with Mr. Field, I continue of the opinion that it would be well to apply about three-fifths of the power to the screw and two-fifths to the paddles, and probably, as the vessel gets light, diminishing a little the expenditure of power on the paddles, and keeping up the full power on the screw. Mr. Field is not in favour of increasing the pressure of steam beyond 12 lbs. or 15 lbs., on the ground that all the mechanical difficulties increase rapidly without a corresponding advantage, particularly where size and weight are not so important. There seems much truth in this.... The possible advantages of a slight increase are not sufficient to justify the risk of the possible new difficulties in a work on so large a scale. Nothing uncertain must be risked. These arguments do not apply to the jacketing and heating, which Mr. Field also deprecated, or rather discouraged, simply on the ground of the trouble and difficulty of effecting it, but he admitted that all experience went to show the advantages of it; and as to the difficulties, which I could not see, they involve no other risk than that of being useless: they cannot do mischief. The heating of the top and bottom of the cylinders, I think, must be particularly important in a short-stroked engine working expansively. In a cylinder of 80 inches diameter and 40 inches stroke, having regard to the time of contact, the area of the bottom will be nearly equal in effect to the surface of the cylinder.
July 19.—After much consideration, I think I feel satisfied that the best construction will be to have strong bulkheads every 30 feet or thereabouts, this distance being dependent on what is required for one set of boilers and its stock of coals; these bulkheads being carried right up wherever practicable—I think every alternate one may be—and then place the main ribs of the ship, and even at least two main deck beams, longitudinal instead of transverse.
February 2, 1853.—Several drafts of ships have been made and much consideration given to the subject, and frequent discussions with various parties. The result of all is that my present views are as follows:—