Carysfort Lighthouse, Key Largo Florida
Completed in 1852, the lighthouse, and the reef on which it is located, is named after the HMS Carysfort, which ran aground at the site in October 1770. Funds for a lighthouse were appropriated by Congress in 1837, but due to the Indian Wars, design was not started until 1848, with completion four years later. The design was started by Captain Howard Stansbury, completed by Major Thomas E. Lannard of the Corps of Engineers. J.W.P. Lewis was the Assistant Engineer, in charge of construction. The well known Philadelphia iron works of Merrick and Son was awarded the construction contract who fabricated and preassembled the skeleton structure at their yard before shipping it to Key Largo. The original lighting aparatus, a "revolving Fresnel lenticular illuminating" device (Augustin Jean Fresnel, a French physicist, designed the first dioptic or lenticular light in 1823, describing it as a "curtain of prisms in front of a light and centered around a bull's eye lens") was constructed by Henry LaPaute in Paris. It was first illuminated on March 10, 1852.
Colonel J.T. Albert, Chief, Corps of Topographic Engineers prepared a site survey in February, 1845 to determine the need for navigational aids along the Atlantic coastline of Florida. Citing extensive marine traffic in the region and mentioning the numerous and trecherous hazards to shipping, he recommended that a series of lighthouses be constructed on the reefs that extend from Cape Florida to the Tortugas, identifying Carysfort Reef as the most dangerous reef in the 200 mile span. Law 3-3- 1848 reauthorized the construction of a lighthouse to replace an outmoded and ineffective light vessel (moved to Brenton's Reef in Rhode Island), this time specifying a "screw-pile lighthouse", for Carysfort Reef. The existing structure was the first of a series of lighthouses built during this period, spaced so that navigators would "not lose sight of one before coming into view of another". Colonel Albert noted that the Eddystone Lighthouse (1706, John Reynolds, rebuilt 1882) had proved its durability, and the design of this structure, along with others in the English and Irish Channels, was suggested as a model for the Carysfort Lighthouse.
The first use of cast iron as as seamark was probably the Carr Rock Beacon (1813-21) off the coast of Fife Ness, Scotland, but the most important influence on the design of the Carysfort Lighthouse is a structure built on Marpin Sands in the Thames Estuary, London. Designed by Alexander Mitchell, who had previously developed a technique for mooring ships using wood screw-piles and tested the principles of wood screw-piles at a lighthouse at the mouth of the river Wyre, Lancaster in 1835.
Mitchell improved on the wood piling by using cast iron screw-piles at Marpin Sands in 1838, where the skeleten consisted of eight peripheral piles centered on a single central pile, all of which formed an octagon (as at Carysfort). Mitchell patented his invention in 1842, and according to A History of Lighthouse "screw-pile lights were built all over the world but particulary in the United States, where they found especial favor". Other screw-pile lighthouse of importance include one at Fowey Rocks (Florida, 1876), similar in design to Carysfort, and Thomas Point, perhaps the largest, at the head of Chesapeake Bay in Maryland.
The Carysfort Lighthouse has been in continuous operation as a First Class light since it was first illuminated in 1852. It is now automated, powered by storage batteries and a small solar panel, mounted on the roof of the light housing. The last lighthouse keeper was replaced during WW II when the structure was used as one of a series of lookout towers in the watch for German U-boats. It has been used recently as a base for research in marine biology and in study of the reefs.