Lightships and Lighthouses

by Frederick Arthur Ambrose Talbot

The contracts were signed in September, 1882, and the task was commenced. The first disaster was a blessing in disguise, for the new engineers were able to turn the mistakes of their predecessors to advantage. They designed a caisson of oval shape, with pointed ends, measuring 46 feet in length by 36 feet wide. It was an elaborate, staunch structure, towering to a height of 60¾ feet when launched. At a height of 8 feet from the bottom edge was a massive flooring built of iron. The space below constituted the area in which the men were to work upon the sea-bed, excavating the sand under compressed air, while the lower rim was a cutting edge, so as to facilitate the sinking of the mass as the sand was removed. The upper part of the caisson was divided into four floors, each of which was set aside for a specific purpose. The lowest was the concrete-mixing chamber; that above carried the machinery and boilers; the third floor formed the living-quarters for the men who worked and slept on the structure; while the top floor formed a deck, and carried two powerful cranes whereby the material was lifted from the boats which drew alongside. Of course, when the caisson had been lowered into the water and was eating its way deeper and deeper into the sand, these platforms had to be moved higher and higher from time to time, as the base of the tun became filled with concrete, the outer walls of the fabric being increased to keep the top well above high-water mark.

When the caisson was completed on shore and sent into the water, it was an impressive-looking monster. The shell itself weighed 245½ tons, and with the various accessories aboard the weight was brought up to some 335 tons. It then had to be loaded down to the required depth for towing, for which purpose ballast in the form of pig-iron, concrete, and bricks, to the extent of another 245 tons, was stowed aboard, while delicate precautions were taken to maintain stability. The combined efforts of 120 men, working day and night for 127 days, were required to erect this caisson, and on April 1, 1883, it was ready for its transportation to the site.

The towing operation was extremely difficult, and the voyage out was full of exciting incident. It was possible to advance only on the ebb-tide, and the towing cables, 5 inches in diameter, were specially manufactured for the operation. Two of the most powerful tugs owned by the North German Lloyd Steamship Company were requisitioned, three other steamers engaged in the conveyance of requirements between tower and shore accompanying the procession. Although the engineers were ready, the weather, with aggravating persistence, refused to clear sufficiently to produce the smooth sea and calm demanded for the safe journey of the ungainly craft. Day after day slipped by, with eighty men on the alert, and with fires banked and steam raised on the vessels, ready to weigh anchor at the first favourable moment. Fifty-five days passed before the weather bureau recommended that the conditions were suitable. Under the foregoing circumstances the expense of this delay may be realized.

THE FOURTEEN-FOOT BANK LIGHTHOUSE, BUILT ON SAND.

The erection of this structure constitutes a brilliant achievement in United States lighthouse engineering.

Directly the intimation was conveyed that the tow could be attempted, there was a scene of indescribable activity and bustle in the Bremerhaven dock, where the caisson was moored. Full steam was raised on the tugs, and at half-past three in the morning of May 26 the mighty steel barrel moved out of the dock. The towing ropes were hitched on, and very slowly the “Colossus,” as the caisson was named, moved down the harbour, accompanied by the whole fleet of nine vessels engaged in construction work, so that the procession was imposing. It dropped down the river without incident, when, the tide turning, anchor was cast, and all was made fast until another advance could be made at four o’clock in the afternoon. But the rising tide was stronger than had been anticipated, and trouble was soon encountered. The caisson, pressed by the current, dragged and strained at the two tugs by which she was being towed, causing them to slip their anchors. It was an anxious moment. The two vessels could not hold the “Colossus”; in fact, they were being towed backwards by it. Hurriedly another tug was called up, and helped in the effort; but although the three steamers put on full steam ahead, they failed to keep the mass in check. Another tug was signalled, and then, under the combined effort of 350 horse-power, driving for all it was worth against the current, the four vessels mastered the swing of the scurrying water, and had the “Colossus” under control.

A little later the procession continued on its way to the North Sea, but when the boats came up with the Hoheweg lighthouse further disquieting news was received. The keepers signalled that the barometer was falling, and that a thunderstorm was hurrying across the North Sea from England. Anchors were thrown out hurriedly, and everything made snug and tight for the approaching storm. It burst with fearful severity. The waves got up, the wind blew with fiendish velocity in terrifying gusts, and the rain tumbled down in sheets. The engineers were on tenterhooks the whole hour and a half the storm raged, as they foresaw lively times if the unmanageable hulk broke loose. But the “Colossus” rode the gale as quietly as if moored to a wharf in dock. The storm, however, upset all calculations for the day. There was no possibility of getting the caisson out and sunk before nightfall, so the engineers prepared to pass the night at anchor, and to start off again with the dawn. The weather, ruffled by the thunderstorm, refused to settle down until a further day and night had been wasted. Then, at 7.30 in the morning, on a favourable tide, anchors were weighed, and, steaming hard through a broken sea, the tugs conveyed the caisson on its journey. At last the procession reached the buoy marking the site. The caisson was brought to rest, the water was admitted gently through the valves, and slowly, steadily, and vertically, the shell sank lower and lower, until a scarcely perceptible shock conveyed the intimation that it had touched bottom.

The most anxious part of the task was consummated with complete success: the caisson had been got to the site and sunk. Then the task of burying it deeply and irremovably in the sand was hurried forward. Workmen descended into the space beneath the bottom floor and the sea-bed. Under compressed air they excavated the sand within the area to permit the cutting edge to sink lower and lower. The sand, as removed, was lifted to the top of the “Colossus” and discharged overboard. Meanwhile the concrete-mixing machine got busy, and the stone heart of the tun was fashioned rapidly. Under this increasing weight the sinking operation was assisted very appreciably. By the middle of October the work had been advanced to such a stage that the total weight of the structure had been increased to over 3,350 tons, and the top deck of the caisson, which had grown in height by the attaching of successive rings of plates, was about 99 feet above the cutting edge, which had buried itself to a depth of 51 feet below low-water. Then work had to be abandoned, as the autumnal gales sprang up. The whole of the staff, with the exception of two men, who mounted guard over the work, were taken back to Bremerhaven. The gales increased in fury, culminating in a tempest similar to that which had destroyed the first caisson. Remembering the fate of that enterprise under such fearful pounding from wind and wave, the Harkort engineers naturally were somewhat anxious concerning the welfare of their handiwork under identical conditions. But the new creation was overwhelmingly strong where its predecessor was weak, although the seas, baffled in their efforts to upset the caisson, did not fail to leave their mark by knocking the superstructure and scaffolding about somewhat, as well as carrying away a few weighty pieces of the top hamper.

Work was resumed in February, 1884, and continued more or less regularly until November. Interruptions were of frequent occurrence, so that only about one-quarter of the time available could be turned to useful account. The structure which had been towed out of Bremerhaven a year previously had disappeared from sight, the rim of the barrel built on dry land being about 4 feet below water; but, of course, as the work proceeded and the caisson sank, its walls were extended upwards, as already explained. When the structure had been sunk to its designed depth, the steel shell was 107½ feet in height, from the cutting edge to the top projecting above the water, and nearly 40 feet of its height was buried in the Rothersand. To sink it to this level required the removal of 3,000 cubic yards of sand from beneath the bottom floor of the structure; while 49,100 tons of material were brought out from Bremerhaven and built into the steel shell to render it a solid elliptical mass, with the exception of a short central hollow space which has a narrow conduit connection with the outer sea, and which, fitted with a float, acts as a tide-gauge which may be read in the lighthouse. From this massive concrete pedestal rises the tower proper, which at the base is circular, with a diameter of 33¾ feet. This base rises in the form of a graceful concave curve to a height of 26 feet, and is solid except for two water-tanks. At the entrance level the tower is 23 feet in diameter. Above this are disposed four floors, comprising the cellar, storeroom, kitchen, and living-quarters for the men, crowned by the lantern, the gallery of which is 80½ feet above low-water.