Screwpiles: The Forgotten Lighthouses

Lazaretto Point, where screwpile lighthouses were prefabricated and shipped by barge to their final site

Lazaretto Point Light – Screwpile Cottage Prefabrication Lazaretto Point is a stretch of land across from Fort McHenry in the Baltimore harbor. In colonial days, the point was the site of a hospital for those with contagious diseases. On March 3, 1831, Congress provided $2,500 to erect a beacon light on the point. By that time, the quarantine hospital was closed. In 1863, a depot opened next to the lighthouse to serve as a storehouse for resupplying other Chesapeake Bay lighthouses. The advantages expected from the establishment of the depot were not immediate, however, as military authorities appropriated most of the facility to serve as a munitions depot for Union forces embroiled in the Civil War. After the cessation of hostilities, however, the depot at Lazaretto Point prefabricated screwpile lighthouses and assembled caisson foundations. Barges towed the cottages and foundations to their sites on the Chesapeake Bay and its rivers. 19 The screwpile design had its own terminology, technology, and screw-cylinder design. The term “screwpile,” used generically, refers to all foundations driven into the bottom to support a lighthouse structure. The actual foundations included wooden piles (with a helical screw carved into the lower end of the pile) driven or screwed

into the bottom, piles encased in an iron cylinder fitted with a helical flange, and iron cylinders alone fitted with a helical flange. In many cases, as with the 1870 rebuild of Point of Shoals and White Shoal, iron cylinders were fitted with a helical flange and screwed into the bottom. Those cylinders, designed with an increased pitch of the screw flange at the bottom of the pile, also had a single flange instead of a double flange. The flange, cast separately, had a recess cut into the surface of the cylinder and the screw flange bolted to the cylinder from the inside. The total cost of using the heavier cast-iron cylinders, instead of wood pilings with a cast-iron sleeve, was lower because of the labor saved by not having to drive a wooden pile. Actual Screwpiles It took the construction crew about two days to screw the eight cylinders 10 feet into the bottom. That screw-cylinder design proved to be substantial enough that the foundations are still in place at White Shoal, Point of Shoals, and Deep Water Shoals, not quite 150 years later.

Work finished on both White Shoal and Point of Shoals on June 24, 1871. The old structures were taken down and the iron pilings removed to be stored at Lazaretto Depot.

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