The structure comprises the main building, including the living-quarters, supported upon piles disposed in two rings, an inner and an outer, about a central pile, the whole being well braced together. The shape is octagonal in plan. From the roof of the living-quarters, to which point the outer piles are carried vertically from the sea-bed, these members rise with an inward rake, forming an octagonal pyramid, with the lantern and its room below forming the apex.
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.