The life of Isambard Kingdom Brunel, Civil Engineer Part 34

_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 mids.h.i.+p section of about 1,800, and a length of 700, I a.s.sume 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 ?; 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, diminis.h.i.+ng 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 s.h.i.+p, and even at least two main deck beams, _longitudinal_ instead of _transverse_.

_February 2, 1853._--Several drafts of s.h.i.+ps 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:--

The s.h.i.+p, all iron, double bottom, and sides up to water line, with ribs longitudinal like the Britannia tube. I have not been able to devise any good mode of determining the relative amount of friction of a copper and an iron surface; and, although I believe in copper, it would not do to act on mere belief. I therefore at present settle iron, the surface being carefully made smooth. Doubts have come across me also as to whether with a very long surface the difference between the smoothness will so much affect the total resistance. Is not a film of water, after a certain distance, carried with the body? and, if so, its greater or less roughness, if not producing currents, is almost unimportant. Would there be any difference in the resistance of a fine file or a rough one drawn through tallow, if they both covered themselves with grease?

Is there any similarity? As to size, if we are to go round the world,[148] I do not think we can do with less than--length, 730; beam, 85; draught deep, 34; and I a.s.sume a nominal horse-power of engines equal to 1 of the sectional area at 30 feet; but, taking consumption as a better measure, and a.s.suming that every possible economy is practised, and every refinement introduced that can produce economy, I shall a.s.sume 7 lbs. per hour per nominal horse-power, or say 008 ton per day per horse-power; and as I a.s.sume the horse-power to be 1 sectional area, it makes the consumption =01 ton per day per foot of sectional area. And this is a very large allowance and ought to ensure a very high speed. In order to effect the utmost economy, I should work up to 20 lbs.

steam (calling it 16 lbs.), cutting off certainly at ? the stroke, and adopting every precaution to keep the steam hot and the condenser cool. The latter depends, I believe, solely upon the perfect dispersion of the injection water, so that the condensation of the steam may take place suddenly, otherwise the same amount of water may condense the steam _in time_, the same amount of heat be given off, the same quant.i.ty of injection water used, and yet the condenser be always full of steam at a good pressure. It might be well worth the experiment to try the effect of a large injection at the moment of the exhaust port being opened; but above all things I believe the heating of the steam to be important; and for this purpose I should jacket the steam pipes and cylinders top and bottom, and heat with high pressure steam, say at 60 lbs.--I have increased this pressure the more I think of it; 60 lbs. would be above 300 degrees, and 20 lbs. not quite 260 degrees; therefore there would be a full 40 degrees of surplus to ensure the temperature. I have a great tendency to believe in the advantage of further heating even, which might be done by a Perkins' arrangement of hot water; but possibly the new conditions, as regards oiling, &c., might involve difficulties not desirable to introduce in this case. In the boilers it will also be necessary to adopt every refinement which has been found really to answer, although not always adopted; above all, every means of keeping them clean--sc.u.m pans, and Field's exchanging apparatus. But what would be even more effectual would be some easy means of removing a whole bundle of tubes and replacing them by clean ones; and surely this would not be difficult, the tubes being large and with plenty of s.p.a.ce, so that a man could pa.s.s his arm between. A rather important addition to boilers would also be a means of blowing off without noise.

Several modes would seem to be possible, but whatever plan is adopted, it should be one which is completely self-acting, and perfectly effectual when used suddenly and without any preparation, and at a moment of confusion and alarm. Blowing through a wire gauze pipe would probably be as likely a way as any.[149]

The more consideration I give to the subject the more disposed I am to adopt oscillating engines for both screw and paddles. The extreme simplicity and small number of parts, and compactness, and the direct action of every resistance to the force which it is wanted to resist, seem to leave nothing to be desired, and would seem to make it a better and more mechanical arrangement of a cylinder and crank than any other, quite independently of the object for which it was originally designed, which was simply 'stumpiness.'

_February 21._--The original line (to Calcutta) seems likely, after all, as usual with most original ideas, to be the best; at all events, so good that the vessel must be built to be able to go there. The dimensions best fitted for this would seem to be--length, 700 feet; beam, 85 feet; depth of hold, 58 feet; screw, 24 feet; paddle 60 feet. If arranged for Calcutta, we must arrive there on an even keel, and therefore, to maintain the most equal level for the paddles, they must be kept well forward, and the change princ.i.p.ally at the stern. Engines indicated horse-power 8,000; steam at 25 lbs.; auxiliary steam at 60 lbs.

The s.h.i.+p to be lighted with gas, to be thoroughly ventilated by mechanical means, having large air trunks, with small pipes and valves to each cabin, with the means of warming this air in cold lat.i.tudes and seasons, and cooling it in the more frequent cases of hot climates. The s.h.i.+p must be steered from the forecastle, whence a perfect look-out must be kept with fixed telescope, &c., and speaking pipes and bells to the engine rooms.

_March_ 14.--At a meeting of the Committee, held this evening here, the several costs and qualities of four different sizes of s.h.i.+ps, of which all the calculations had been made by me, namely:--

No. Length Breadth Mid. Sec. Draught 1 663 799 1,646 24 2 634 7639 1,640 25 3 609 735 1,639 26 4 730 87 2,090 28

were discussed, and the No. 1 determined upon as the best under all the circ.u.mstances. I should propose, therefore, to make the dimensions of No. 1:--length, 680 feet; beam, 81 feet, to be swelled to 83 feet; extreme draught, 30 feet; mean, 24 feet; daily consumption, say 200 tons.

This s.h.i.+p can carry her coal to Calcutta, and arrive and leave with only 21 feet 6 inches draught, having 9 days' coal and 3,000 tons cargo; or she could first go to Australia and back, without or with very little cargo out, and consequently would take out as much cargo as you might choose to send coal for her to Australia....

These dimensions are worked out in the design No. 5 (April 9, 1853), but they would be better for a slight increase, if the 83 feet were made 85 feet, and the 680 feet were made 700. We should have an increase in capacity of 83 680=56,440 to 85 700=59,500, or 6 per cent. of displacement. This would bring the displacement at 32 feet draught up to 31,250 tons.

_March_ 22.--Settled the various dimensions of scantlings with S.

Russell to enable him to direct drawings of all details to be got out.

_April_ 28.--We are now seeking tenders for engines and s.h.i.+p 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 s.h.i.+p 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 s.h.i.+p and her engines.

The following selections from Mr. Brunel's memoranda ill.u.s.trate the progress of the design during the early months of the year 1854:--

_February 25, 1854._--The details of construction, both of engines and s.h.i.+p, 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 s.h.i.+p are far from being satisfactorily settled. I have no record of the many consultations. .h.i.therto held on the subject, but shall hope to keep one hereafter.

On the 6th inst., some of the drawings of the s.h.i.+p 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 s.h.i.+p. Some other consultations have been held, and again to-day (February 26) I have spent some hours at Millwall.... Discussed the details of a mids.h.i.+p 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 s.h.i.+p-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 1,200_l._ of money in first cost, and 40 tons of cargo freight--at least 3,000_l._ a year. The principle of construction of the s.h.i.+p 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 s.h.i.+p, and none merely for the purpose of facilitating the framing and first construction.

In the present construction of iron s.h.i.+ps the plates are not proportioned to the strength required at different parts, and nearly 20 per cent, of the total weight is expended in angle irons or frames, which may be useful or convenient in the mere putting together of the whole as a great box, but is almost useless, or very much misapplied, in affecting the strength of the structure as a s.h.i.+p.

All this misconstruction I forbid, and the consequence is that every part has to be considered and designed as if an iron s.h.i.+p had never before been built; indeed I believe we should get on much quicker if we had no previous habits and prejudices on the subject.

_March 3._--Mr. Blake [_of the firm of Messrs. James Watt and Co._], called, and went fully into the general drawings which he brought. On the necessity of large surfaces he quite concurred with me. The extent to which such a general principle should be carried is of course very difficult to determine; my idea is that it has never yet been approached....

_March 10._--Engaged all the afternoon at Millwall.... Settled and signed the drawings of crank and piston rods. Went into many details of s.h.i.+p....

The extracts from Mr. Brunel's correspondence which follow, have been selected as containing a definition in his own words of the position he held as Engineer to the Company by which the great s.h.i.+p was built.

_Letter to the Secretary of the Eastern Steam Navigation Company._

[This letter was written in consequence of a resolution of the Directors, asking Mr. Brunel to recommend them a resident engineer, in order that constant supervision might be exercised over the works, and frequent reports made to the Board.

The Directors rescinded their resolution; but this letter is inserted as showing, in clear and forcible language, Mr. Brunel's view of the nature of his duties and responsibilities, and as laying down what in his opinion ought to be the relations between the Directors of a Company and their Engineer.]

August 16, 1854.

...It surely cannot be necessary to remind the Directors that the very unusual stake which as a professional man I have been willing, perhaps imprudently, to risk on the success of this project--I mean stake of professional character, not mere pecuniary risk--must secure a much greater amount of attention to any step, and supervision of any detail on my part, than any ordinary professional engagement would obtain; the heavy responsibility of having induced more than half of the present Directors of the Company to join, and the equally heavy responsibility towards the holders of nearly half of the capital, must ensure on my part an amount of anxious and constant attention to the whole business of the Company which is rarely given by a professional man to any one subject, and, as it seems to me, ought to command a proportionate degree of confidence, or rather command entire confidence, in me, if any at all, for in such a case there can hardly be any medium.

The fact is, that I never embarked in any one thing to which I have so entirely devoted myself, and to which I have devoted so much time, thought, and labour, on the success of which I have staked so much reputation, and to which I have so largely committed myself and those who were disposed to place faith in me; nor was I ever engaged in a work which from its nature required for its conduct and success that it should be entrusted so entirely to my individual management and control....

The Directors have a right to expect, and will ever receive, from me the fullest information and the most unreserved communication upon all points as they arise, as from one who feels the responsibility of being their sole professional adviser in a very important and serious business, in which we are all embarked, and all deeply interested; but I cannot act under any supervision, or form part of any system which recognises any other adviser than myself, or any other source of information than mine, on any question connected with the construction or mode of carrying out practically this great project, on which I have staked my character; nor could I continue to act if it could be a.s.sumed for a moment that the work required to be looked after by a Director, or by anybody but myself or those employed directly by me and for me personally for that purpose.

If any doubt ever arises on these points I must cease to be responsible, and cease to act.

_Letter to the Secretary of the Eastern Steam Navigation Company._

[In explanation of the following letter it need only be stated that an elaborate article on the great s.h.i.+p appeared in one of the London newspapers of November 1854. Mr. Brunel's name was only once mentioned throughout the whole of it, and in these words: 'Mr.

Brunel, the Engineer of the Eastern Steam Navigation Company, approved of the project, and Mr. Scott Russell undertook to carry out the design.']

November 16, 1854.

Since I wrote to you I have taken the trouble to read through the long article in the----, and am much annoyed by it. I have always made it a rule, which I have found by some years' experience a safe and profitable one, to have nothing to do with newspaper articles; but then, if on the one hand the works I have been connected with have rarely been puffed (never by me), they have also been rarely affected by misstatements; as such notices, when not inserted by interested parties, are always slight and unauthentic, and drop without producing any effect. This article in the----, however, bears rather evidently a stamp of authority, or at least it professes to give an amount of detail which could only be obtained from ourselves; and if, as I think is the case, copies of it have been circulated by us, it may acquire the character of being an authorized statement; and, as such, I am individually much annoyed by a great deal that is in it, and by the omission of much that might with propriety have been introduced.

What is constantly repeated or implied, and remains uncontradicted, is at last received almost unconsciously as fact even by those who have the means of knowing it to be incorrect, if they thought about it; and, although from system I have never interfered with newspaper statements, it has not been from any affected or real indifference to public opinion, perhaps it was more from pride than modesty, and therefore I am by no means indifferent to a statement which would lead the public, and perhaps by degrees our own friends, to forget the origin of our present scheme, and to believe that I, happening at the time to be the consulting Engineer of this Company, which I was not, and having had no peculiar connection with previous successful improvements in steam navigation, allowed them to adopt some plan suggested by others, who I suspect, if even such were the case, would never appear to share with me the responsibility if any failure should result. Of this certainly I have no fear, but at the same time I am desirous of something more than mere immunity from blame.

I not only read this article once, but I was so struck by the marked care shown in depreciating those efforts which I had successfully made in advancing steam navigation, and mainly on the strength of which no doubt I originally obtained the confidence of the Directors, which induced them to enter upon our present bold undertaking, that I read the paper a second time, and for the very reason that I have for so many years shunned public writings, namely, to escape misstatements, I feel compelled on the present occasion to take some steps publicly to correct those erroneous impressions, which must be created by a doc.u.ment having the appearance of emanating from ourselves....

The objectionable points that I refer to evidently did not strike you, and that is a strong proof how easily incorrect impressions insinuate themselves unawares; but I feel strongly that a judicious friend would not have failed to do justice to the spirited merchants of Bristol, who, in spite of the strongest condemnation of the plan by the highest authorities, and the ridicule of others, persevered in building and starting the first transatlantic steamer. The circ.u.mstances as regards the 'Sirius' are coloured so as to be quite incorrect; and the same friendly hand would not have thrown ridicule, and that by a positive false statement, upon that which he at the same time admits to have been the means of almost introducing two of the greatest improvements in steam navigation. A writer wis.h.i.+ng success to our enterprise would not have omitted to mention that I had a claim to public confidence on this occasion, for the reason that I was at least the princ.i.p.al adviser in those previously successful attempts.