Our structural engineer, John Moore, has passed along a writeup about the lantern tie downs that he designed. Tommy Graham, a restoration contractor who has spearheaded the effort to preserve the lighthouses, installed this work in 2013.
Tommy Graham and I both agreed that one of the most important and one of the easiest tasks for the lighthouse would be to tie the lantern down to the masonry portion of the tower below. Its connection to the top was precarious, and we were worried the lantern could be blown off the tower by the next passing hurricane, thus losing the lantern and then having the top of the tower exposed, letting the elements into the tower and accelerating the deterioration of all the parts.
The top of the wall where the lantern was originally tied down to masonry is thin, cracked, and being greatly affected by the original rusting (and expanding) iron rod ties embedded in the top of the wall. Our tie down system consisted of three rods connected to the perimeter of the lantern roof, which were then connected to a cable at the turntable level and which extended down a central hole and below into the hollow main stair post of the tower. The cable extended all the way to the bottom of the post and was connected there; thus the lantern’s tendency to blow off was resisted by the weight of the center post and all the treads. When Tommy went to do the work, he simplified the design by connecting the cable to a pair of beams two platforms below the turntable, therefore using the weight of the masonry tower for resistance. We then strengthened the wall below the lantern by adding wood bracing in the top of the tower (a compression ring) and strapping on the outside (a tension ring).
On my last trip to the lighthouse we took the measurements for all the parts of the work and Hillary King drew it all up. Tommy did the work himself in a great feat of climbing and craftsmanship!
The tie downs extend diagonally through the lantern. The top of the masonry has been strapped together.