Lightships and Lighthouses

by Frederick Arthur Ambrose Talbot

The underwater work was the most difficult, owing to the situation and the climatic conditions. Seeing that the nearest land is sixteen miles distant, it was impossible to carry the men to and from the scene of their labours every day when the weather permitted. A base was established on the coast for the preparation of materials and as a point for shipping all requirements to the site, but the men were accommodated with special facilities upon the spot. Here a temporary staging was built on piles, on which platform a large hut was erected to provide quarters for the men, as well as a workshop.

The piles forming the main support to the building were made 50½ feet long, and hollow. The concrete, composed of broken granite and Portland cement, encased a steel skeleton, consisting of four longitudinal round steel rods, 1¾ inches in diameter, laid at the corners, and laced together with steel wire ³/₁₆ inch thick. Eight of these piles were made 18 inches square, while nine were 24 inches square, and each was fitted with a pointed end to facilitate driving into the sea-bed.

As these piles were prepared on shore, their transference to the site was a pretty problem in itself. Ordinary methods of transport were impracticable. The engineer overcame the difficulty in an ingenious manner. He built up a raft of barrels, twenty-six of which were lashed together in two rows, between which the pile was laid flat and evenly. The raft was built upon peculiar lines, so as to facilitate the unshipping of the pile when it reached its destination. It was divided into four sections, each of which could be detached without disturbing the other three parts. The raft and its pile were towed out to sea by a steamer, and when the work was gained the raft was cast off, to be floated under the staging and to the exact point where it was to be set up. A chain sling was lowered from the platform and attached to the head of the pile, and the lashings to the first section of the raft were released, thus permitting the strapped barrels concerned to float away and to be recovered. The pile was then slowly and carefully hoisted at the head, the second part of the raft being released when the pile had gained a certain height. This procedure was repeated until finally, when the last part of the raft was freed, the pile hung free, as vertically true as a plumb-line, with the pointed foot resting on the sand. In order to send it truly into the sea-bed, heavy timber guides were set up, and as the pile descended it was frequently tested with the plummet, to see that it was sinking in an absolutely perpendicular manner.

COMPLETING THE ONE FATHOM BANK LIGHTHOUSE IN THE MALACCA STRAITS.

The keepers live on the lower floors. The upper floor beneath the lantern is the service room.

The piles were sunk into the soft sea-bed by means of water-jets, which, playing about the foot of the pile, burrowed a hole into which it could move downwards. A depth of 15 feet had been considered necessary to secure the desired rigidity, and as a rule the pile could be driven to this depth in about four hours. When the pile-driving commenced, however, it was found that the sandbank had undergone a marked change since the surveys were made. Erosion had been very active owing to the currents having been checked by the obstructions which the legs of the staging offered. Under these circumstances a novel experiment was made upon the site. One of the piles was lengthened by 14½ feet, to be driven to its limits, just to ascertain how far it would go into the sand. This in itself was a somewhat daring undertaking, seeing that the tiny colony on the staging did not possess the facilities which were available on shore for the work. However, it was accomplished satisfactorily, and when the pile was sunk it was found to descend another 13½ feet, where it touched hard rock. This discovery brought about a modification in the plans. As a solid foundation could be gained at a depth of 28½ feet, and as the piles could be lengthened successfully upon the site, it was decided to extend all the piles to a complete length of 64½ feet, and to drive them down to the hard bottom. When the piles were all lowered, they were subjected to four blows from a “monkey” weighing 2½ tons, dropped from a height of 4 feet. But these four final blows only drove the piles from ¼ to ⁷/₈ inch farther into the sea-bed, whereas, according to the specification, a margin of 1 inch was allowed for this test.

The diameter of the tower at the base is 40 feet, and heavy bracing is introduced at a point 4 feet below high-water to hold the fabric together, and to supply the requisite strength and rigidity. At a height of 21 feet above this main bracing is the floor of the superstructure, comprising an octagonal two-floor building, surrounded by an overhanging gallery, built on the cantilever principle, 5 feet in width, which forms the landing platform. The two floors have a total height of 24 feet, and constitute the keepers’ home. The roof is flat, in order to facilitate the collection and conduct of rain-water into two ferro-concrete cisterns, each holding 1,000 gallons. The lower floor is devoted to housing stores, oil, etc., while the upper story forms the living-quarters. The roof is caused to overhang a distance of 4 feet on all sides, thereby providing a flat surface 44 feet across. From this point the eight main columns of the building slope inwards, until, at a height of 30 feet, they have a diameter of 18½ feet, where the lantern is introduced. The lower part of the latter constitutes the service-room, and leads directly to the lantern above. Access to the different levels is afforded by means of a teak-wood staircase, while that leading from the entrance floor to the water for landing purposes is hinged, so that it may be accommodated to the condition of the tide.

The lantern, which weighs 17½ tons, is of the modern type, and is more powerful than that of the 1874 light, which it displaced. The white light is thrown in groups of flashes every fifteen seconds, and the warning is visible from the deck of a vessel some fifteen miles away. The central pier, which carries a great proportion of the total weight of the tower, and which extends continuously from the bed-rock foundation to the lantern-room, is solid to the roof of the living-quarters. Above this point it is hollow, having a bore of 12 inches, and in this space the weight actuating the revolving mechanism of the light moves up and down.