Lightships and Lighthouses

by Frederick Arthur Ambrose Talbot

In 1855 General Barnard, one of the most illustrious engineers which the United States has ever produced, brought forward the plans for a structure which he thought would resist the most formidable attacks of wind and wave. He took Rudyerd’s famous Eddystone tower as his pattern. This was perhaps the strongest design that could be carried out against the sea, having one weak point only—it was built of wood. General Barnard contemplated a similar structure for Minot’s Ledge, but in masonry.

The Lighthouse Board, which had recently been inaugurated to control the lighthouses around the coasts of the country, examined the idea minutely, and submitted the design to the most expert criticism and discussion, but all were so impressed with its outstanding features that they decided to support it whole-heartedly. A minute survey of the rock was prepared, and the plans were straight away perfected for the preparation of the masonry on shore. So carefully was this work carried out, that, with the exception of a few blocks of masonry constituting the foundations, which had to be prepared on the site, and some slight variations in the method of construction, the original ideas were fulfilled.

Work was commenced in 1855, the building operations being placed in the hands of B. S. Alexander, at that time Lieutenant of Engineers, and the successful completion of the work was due in a very great measure to his ability and ingenuity, because the whole undertaking was placed in his hands and he had to overcome difficulties at every turn as they arose.

The builder was handicapped in every way. First there was the brief period in which operations could be carried out upon the site, the working season extending only from April 1 to September 15 in each year. This is not to say that the masons were able to toil upon the rock continuously every day during this interval—far from it. In order to get the foundations laid there were three essentials—a perfectly smooth sea, a dead calm, and low spring-tides. Needless to say, it was on very rare occasions indeed that these three requirements were in harmony. As a matter of fact, they could occur only about six times during every lunar month—three times during full moon, and three at the change. Even then, either the wind or the sea intervened to nullify the benefits arising from the lowest tides. So much so that, although work commenced at daybreak on Sunday, July 1, 1855, only 130 working hours were possible upon the rock before labours ceased for the season in the middle of the following September.

TENDER LANDING BUILDING MATERIAL UPON THE TILLAMOOK ROCK.

A derrick has been provided to facilitate these operations, while a stairway leads from the landing point to the lighthouse.

On gaining the rock, Lieutenant Alexander decided to make use of the holes which had been driven into the granitic mass by Captain Swift to receive the piles of the previous structure. The twisted and broken pieces of iron were withdrawn and the holes cleaned out. Simultaneously the upper surface of the rock was pared and trimmed by the aid of chisels, which was no easy task, because at times the masons were compelled to manipulate their tools as best they could in two or three feet of water. This preparation of the rock to receive the base constituted one of the most notable features of the work. In the greater number of other outstanding achievements upon sea-rocks the surface of the latter has been above the waves at lowest spring-tides, whereas in this case a great part of the foundation work was continuously submerged.

This preparation of the rock-face necessitated the final trimming and shaping upon the site of many of the masonry blocks forming the root of the tower. They could not possibly be prepared ashore to bring about the tight fit which was imperative. Accordingly, all but the bottom faces of the blocks were prepared in the depot on the mainland, and they were then shipped to the ledge for final paring and trimming.

The attachment of the bottom courses to the rock-face was carried out very ingeniously. Bags of sand were brought on to the rock and laid around the spot upon which a particular block of stone was to be laid. The sacks, being filled with sand, were pliable, so that, when deposited, they adapted themselves to the contour of the ledge, and prevented the water making its way in under the rampart. The water within this small dam was then removed, sponges being used in the final emptying task, so as to suck out the salt sea from the cracks and crevices, leaving the surface on which the block of stone was to be laid quite dry. A film of cement was then trowelled upon the rock surface, and upon this was laid a sheet of muslin. The inclusion of the muslin was a wise precaution, because while the work was in progress a wandering wave was liable to curl over the rock, swamping the small dried space, when, but for the presence of the muslin, the cement would have been carried away. At the same time the cement was able to penetrate the meshes of the muslin when the stone was deposited, so as to grip the surface of the latter and to hold it tightly in position.