April 28.—We are now seeking tenders for engines and ship of the following dimensions:—Length, 680 feet; beam, 83 feet; mean draught, about 25 feet; screw engine, indicated horse-power 4,000; nominal horse-power, 1,600; paddle, indicated horse-power, 2,600; nominal horse-power, 1,000; to work with steam 15 lbs. to 25 lbs.; speed of screw, 45 to 55 revolutions; paddle, 10 to 12.
Among the details of improvements still to be considered are the receiving through measures the coal from the bunkers, and running it on tramways and waggons to the front of the fires, thus at the same time measuring out accurately the hourly consumption, and saving labour; but a still more important object, the use of clean water—that is, using the same water over again—is well worth considering; and it is well worth the experiment, whether cooling down the water of condensation to use again is not in fact the easiest way. With an unlimited supply of cooling water this ought to be easy.
August 7.—Memoranda for engines.—Very sensitive governors to be applied to both engines to prevent running away.
November 18.—It is curious that the above should be the last memorandum, as I now open the book to make the same in consequence of the accident to the ‘Agamemnon.’[150]
There can be no reason why a sensitive governor should not act in less than one revolution of the crank, and act upon a tumbler which should shut off instantly the expansion valve. There should be two such governors, one to each end of the crank shaft, and they should work direct from a spur wheel from the shaft without any intermediate shafting, to give elasticity, or to risk breaking. (Query, hydraulic governors?)
The auxiliary engine and boiler to be at least 20 feet from bottom, and, better still, above load water line, or so boxed as to be out of reach of water; so that if the ship grounded and filled, this engine would remain serviceable for pumping or anything else.
The history of the ‘Great Eastern’ has now been traced up to the date of the contracts for the construction of the ship and her engines.
The following selections from Mr. Brunel’s memoranda illustrate the progress of the design during the early months of the year 1854:—
February 25, 1854.—The details of construction, both of engines and ship, involve an immense amount of thought and labour. I have devoted a great deal of time to it already, and yet even the preliminary details either of engines or ship are far from being satisfactorily settled. I have no record of the many consultations hitherto held on the subject, but shall hope to keep one hereafter. On the 6th inst., some of the drawings of the ship and of parts of the engines, having been several times revised and altered, being ready, I spent the greater part of the day at Millwall[151] in going again into them, and settled some parts, such as the dimensions, &c., of cranks, and bearings, general form of engine frame, and some of the general principles of framing and plating of the ship. Some other consultations have been held, and again to-day (February 26) I have spent some hours at Millwall.... Discussed the details of a midship section, the drawings of which were in a forward state; directed that the cabins should positively be made 6 feet 6 inches each in the clear, and the bulkheads made subordinate to this; found that it could be done without difficulty, and without causing any mechanical objections in construction. I am anxious to have some approximate estimates of weights.
It is evident that large weights may most easily be wasted or saved by a careless or close consideration of the best application of iron in every single detail. I found, for instance, an unnecessary introduction of a filling piece or strip, such as is frequently used in ship-building to avoid bending to angle irons; made a slight alteration in the disposition of the plates that rendered this unnecessary; found that we thus saved 40 tons weight of iron, or say 1,200l. of money in first cost, and 40 tons of cargo freight—at least 3,000l. a year. The principle of construction of the ship is in fact entirely new, if merely from the rule which I have laid down, and shall rigidly preserve, that no materials shall be employed on any part except at the place, and in the direction, and in the proportion, in which it is required, and can be usefully employed for the strength of the ship, and none merely for the purpose of facilitating the framing and first construction.