The life of Isambard Kingdom Brunel, Civil Engineer

by Isambard Brunel

It is now necessary to turn our attention to the best mode of removing the ship. I hope in about a fortnight from the present time to be able to give you some opinion upon this point, but it is one requiring much consideration; and until I had the opportunity of conferring with Captain Claxton on the subject, and also had before me all the measurements and data which he has collected, it was useless to attempt it.

The construction of the breakwater will be understood by the following extracts from a report made by Captain Claxton to the Admiralty.

‘Great Britain,’ July 16, 1847.

...Mr. Brunel’s instructions to me were principally by word of mouth; the difficulty to be got over, in his opinion, being the foundation upon sand, varying in depth according to the points or hollow of a substratum of rock, and according to the quarter from which the wind blew.

The foundation could only be made at low water, and as fast as a layer of fagots was laid, it was rapidly pinned down with iron rods, bent at the heads, varying from 9 to 6 feet in length, and driven to the rock under, loaded with stones quarried from the nearest reefs, and upon these, the last thing as the flood came in, chain cables, air-pump covers, fire-bars in large bundles, and the ship’s guns were dropped, care being always taken to have the ends of the chains, and the slings of other heavy matters, fast to the ship. As the tide in smooth water began to recede, or in heavy seas began to lose effect in striking, these iron weights were lifted, and the fagots which were ready were ... placed; and the same process followed tide after tide when the water ebbed sufficiently, which upon the neaps it never did at all, and upon the springs it only did for about an hour, unless there was either no wind at all, or unless the wind blew off the land, or from the West round by the North to ESE. It is necessary, to a proper understanding of the nature of this really large work, to describe a bundle of fagots, lest an idea should be formed that it is a small thing and easily handled. They averaged 11 feet in length, and 5 feet in circumference near the butts, which all pointed one way. When tied in Lord Roden’s wood, many were 13 feet long, and none were taken under 10 feet. A cart of the country with one horse could carry about ten bundles when well lashed, and as they came down there was rarely more than the head of the horse to be seen. Sixpence per bundle, and sixpence for delivery, was the contract; the distance at high water nine miles, at low water six miles; and our sailors made them into large bundles of twos, threes, and fours; now and then we experimented with bundles of eight or even ten, in the middle of which were bags of sand (old guano bags), varying in number, of 2 cwt. each, and sometimes as many as amounted to a ton in weight. These large bundles stood if the water remained smooth; but if, before we could build up to their height with smaller bundles, and, as it were, prop or shoulder them fore and aft, we were caught by a breeze and sea, we found them rolled up to high water mark, or on spring tides four hundred yards; while some are now being hove out of the sand entire, and with the sand bags and sand complete....

Having got the foundation, on which, I may mention, we placed one of the ship’s iron life-boats, 30 feet long, 8 feet wide, and 5 feet deep, and loaded her with stones, and which also, although over bundles of fagots, went bodily down, until only the gunwale was above the level of the strand, we began to build the part which was to save the ship from the blows of the sea, and which I was instructed by Mr. Brunel to bring up to a point to the ship’s gunwale in the form of a large poultice, occupying the whole space under her counter, the whole of the exposed quarter (the port quarter), and inclining inwards from the outside, and declining from the top to the same point forward, to the after end of the bilge keel. I was to be, and was, as careful as I could be to secure as well as to weight down as we built. Chains were secured in many places to the lower bundles of fire-bars sunk in the sand outside all, and these were brought into the arms of the screw, and to ring bolts let into the ship; and rarely were two layers placed without a repetition of the securing and weighting process all the while we had chains to use....

We were frequently beaten; whole masses were capsized, but it was found that even the foundation broke the ground swell, which, instead of having a fair run as it has over the strand, seemed stopped, and to break differently; and certainly the ship was daily eased of the blows of the sea.... Finding the wind keeping on shore, the fagots we placed shrinking, sinking, or settling down, and, notwithstanding the weights and lashings, commonly breaking away, I proposed to try spars. Mr. Brunel acceded, and recommended my trying four long ones, to the heels of which were to be attached chains with a spread of eight feet, the spars being pointed at the heels, the slack of the chains, and the height at which they were stopped to the spars, being intended to be sufficient to embrace about a dozen bundles of fagots, the points of the spars sticking through the foundation below the level of the sand. After placing the first pair of spars at an angle from the gunwale of about 70 degrees, and before the second pair with its fagots could be got in place, and after heaving them down tight with a tackle to each from the head to the gunwale, a heavy sea came with the flood dead on, and although the spars were seven inches square, they stood the blows of the sea, bending in the middle full five feet when heavily struck. This gave me the idea of green trees: firs being the first that occurred to me; first because of their height, and next because in Lord Downshire’s grounds at Dundrum the castle wood consisted of them only, and lastly, because they were cheap and at hand. The spars we fortunately placed, and which stood so well, were American elm, a large balk of which had been sawed in four lengths of 42 feet for framing, for Mr. Bremner’s breakwater.... The lengths required to allow the application of a tackle to the head to heave them tight down to the gunwale, or to the scuttle-holes of the ship, were from 45 to 50 feet. I found that the firs of this length were scarce, and too fine at the head; but on looking in Lord Roden’s wood, a better substitute was offered in the form of beech trees of any size, and a contract was speedily made, and as speedily completed; the carts of the country bringing in one tree at a time, until about eighty were placed at the most exposed point, the quarter, in three rows, the outside row at an angle of 45 degrees. Beech-trees were found decidedly better than firs, or, I believe, than any other description of tree, as their weight was soon found sufficient to keep them in place without the heaving down tackles. They can be got of great length, without being so large and (carting, pointing, and handling considered) so unwieldy a butt as firs, and they are of greater diameter aloft, consequently stronger, and altogether tougher than firs. Having got the whole stern surrounded, and having continued them at from 4 to 5 feet apart up to the bilge keel, or about 80 feet of the ship from the screw, I applied smaller spars (easily and economically obtained from the Tyrella domain, or within half a mile of the ship) laterally and diagonally, and about a foot apart in the former case, and 3 or 4 feet in the latter; the number about 300, of all or any lengths between 15 and 30 feet. While this was about, the fagot process was going on; and before that was completed, I found the foundation with the boat, and its 40 tons of stones, and even the spars, although pointed at the angles, indicated an inclination to move forward through the sheer force of the rollers. To check this, tackles were made fast to three warps out to seaward, with two anchors to each, and brought to the spars with four spans to the inner block. Thus twelve of the largest spars were grappled, the falls taken on board, and all hove tight; the whole of the spars having first been attached to one another by a round turn of a half-inch chain with strong staples, and of course by the lateral spars or spreaders, and their innumerable seizings. Suffice it to say, as regards the spars, that when struck by violent seas from half-flood to half-ebb, they bend in a body from 3 to 4 feet, and spring back after the blow; and this is, I believe, the whole secret of the efficiency of the spar part of the breakwater, which has stood the whole winter, only one having broken, and that because the head took against the topsail yard, lashed along stanchions of the rails as a hold-down for the tackles attached to their heads. As a proof that this is the probable cause of its standing so well, I may refer to Mr. Bremner’s breakwater, which went with the first heavy gale and sea, although made of balks of from 17 inches to 13 inches thick: also to our having ourselves placed a pine spar 9 inches diameter down by the side of the outside tree on the starboard quarter, and which broke in two right in the middle with the first sea that struck it. The sea struck very hard against the spars and framework, from which it was received by the fagots without any shock to the ship worth speaking of. With respect to the fagots, I could not find materials to go on weighting down as we went on piling up.... I therefore ran the remaining fagots up light. No sooner, however, was this done, and a gale came on, than we were compelled to let go the lashings, and to help some of the top ones to escape, as the whole of the unloaded body rose and fell full three feet with the sea, and would have done mischief to the spars and to the ship, by shouldering her quarter, and twisting her. About 200 bundles broke away in this gale. They were, however, all recovered, and placed further forward and low down, and then loaded with stones; about one third of the top space having after this been left open, or one third down from the apex levelled. Shrinkage did much towards this, and breaking in pieces a good deal; so it was not deemed advisable to fill that space again.

About the 1st of May the progress made in lifting the ship by tightening her from the inside, and by lightening her of everything moveable, led me to believe that we should be about getting her off towards the end of this month. I therefore felt that it was time to begin removing the fagot portion of the breakwater.... The process of levelling went on for about three weeks, when all above the loaded portion was taken away. We commenced on that portion from necessity, and found that by no contrivance of purchases and levers could our ten men get up or out more than four or five bundles per tide. This became, and even now is, a serious matter. We have got up all our chains and weights, and nothing remains but the fagots and stones, which are so embedded in sand as to form a mass which is more difficult to move than granite rock would be, as we cannot blast. Twenty labourers have been twenty-one tides at work, by contract, and certainly they have made an impression; but it is not lowered over two feet. The lower portion was made of furze bundles, here called whins, and they are great collectors of sand, and only come up at all by being cut to pieces. I mention this to show that furze and fagots loaded with stones on sand 500 yards from high-water mark, exposed to the sea, will form a foundation on which a building of any weight might be erected....

Mr. Brunel informed me, when I undertook to carry out his views, that there was nothing new in using fagots to stop breaches in sea-walls, as in Holland; and that he saw no reason why they should not stop the force of the sea in protecting ships as well, provided they could be secured, and a foundation got. They were to be made of alders, ash, holly, laurel, oak, or anything tough, to be cut down, and made up green, to be placed with all their leaves on, to be pointed to the sea at their butts; and inside the walls of them, if I may so speak, whin (furze) bundles were to be weighted down, the fagots placed in steps or rows of about 4 feet from the outside to the ship’s gunwale.

As the summer came on, the mode of lifting and floating the ship had to be decided. On this point Mr. Brunel wrote to the Directors:—