The Seven Foot Knoll Lighthouse was originally completed in the Chesapeake Bay in 1856 to mark the entrance to the Patapsco River, an important trade route into Baltimore, Maryland. Unlike most screwpile lighthouses, the house was cast iron rather than wood.
The first screwpile lighthouse was built at Brandywine Shoal, Delaware, in 1850. They soon became a popular construction type in the protected waters of the Chesapeake Bay and Carolina Sounds, often replacing lightships. They worked well where the soft bottom surface could not support a masonry tower and were much less expensive to build.
Unfortunately the screwpile towers, including Seven Foot Knoll, were vulnerable to ice flows and were often damaged in storms. Many were replaced with towers that had more durable caisson foundations.
Today the Seven Foot Knoll Lighthouse is open to the public as a museum managed by the Historic Ships of Baltimore. It is one of three screwpile lighthouses that have been brought ashore as museums. The others are Drum Point Lighthouse at the Calvert Marine Museum, Solomons, Maryland, and Hooper Straits Lighthouse at the Chesapeake Bay Maritime Museum, St. Michaels, Maryland.
The last extant, intact screwpile lighthouse still in its original location is Thomas Point Shoal Lighthouse near Annapolis, Maryland. This tower is accessible only by boat; however tours are offered during the warmer months through the U.S. Lighthouse Society.
Submitted by Candace Clifford, December 1, 2016
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Candace was the US Lighthouse Society historian from 2016 until she passed away in August 2018. For 30 years, her work involved lighthouse history. She worked with the National Park Service and the Council of American Maritime Museums. She was a noted author and was considered the most knowledgable person on lighthouse information at the National Archives. Books by Candace Clifford include: Women who Kept the Lights: a History of Thirty-eight Female Lighthouse Keepers , Mind the Light Katie, and Maine Lighthouses, Documentation of their Past.