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The cylinder for Thimble Shoals Light Station was pre-assembled in the factory in 1913 (top) and shown here as part of the completed station in 1914 (bottom). National Archive photos.
Offshore Lighthouse Construction Types--Caisson

The caisson construction method for lighthouses is based on the idea developed by Lawrence Potts, an English physician and inventor, who in 1845 sank a section of hollow tubing from the surface of the ocean to the sea floor. He then attached a powerful pump to the open end extending above the water, and as he pumped air and water from the tube, it drew up sand which allowed the tube to sink by gravity deeper into the sea bottom. This idea was adopted by Charles Fox, a civil engineer, for sinking railroad bridge supports. The method was then employed in 1850 during the construction of bridge support towers at Rochester, New York. Workmen soon discovered that large rocks obstructed the descent of the tube so the engineer in charge, J. Hughes, reversed Pott's process. He pumped air into the tube forcing the water out so his men could descend into the tube and remove the rocks, sand, and mud, allowing the tube to sink under its own weight into the river. The foundation for the Brooklyn Bridge in New York City, as well as many bridge foundations were built using this same pneumatic method. Pott's modified method was also used to build caisson lighthouse foundations, particularly in unconsolidated soft bottomed environments such as muds or sands .[1]

The caisson lighthouse type used a large cast-iron cylinder, which was sunk on the bottom and filled with rock and concrete to form a foundation. Where bottoms were harder, contained rocks, and/or needed greater depth of penetration into the substrate, the pneumatic process was used for 11 light stations. The substrate within the caisson was removed and the caisson allowed to sink further into the bottom. Caisson lighthouses were more complicated and on average about four to five times more expensive to build than screwpile lighthouses, but they were better able to withstand the pressure of flowing ice. For this reason, many screwpile lighthouses in the Chesapeake and Delaware Bays were replaced with caisson type lighthouses. The Sharps Island (1882) caisson lighthouse built to replace the 1866 screwpile lighthouse destroyed by ice in 1881, leans from ice damage which occurred in 1897. Twelve caisson lighthouses were built on the Chesapeake Bay, five of them replacing screwpile type lighthouses in Virginia waters and two in Maryland waters. The Sabine Bank Lighthouse (1905) in Texas is the most exposed, located 15 miles offshore in the Gulf of Mexico the only successful caisson south of the Chesapeake Bay.

On these caisson platforms the builders erected several different styles of lighthouse towers. In Chesapeake Bay two dominated: conical metal lighthouses, often called coffee pots because their configuration suggested such, and brick structures suggestive of the Second Empire style. Elsewhere the superstructure was a slightly conical squat tower. All of these structures had work and storage space, and adequate water storage, as well as living quarters for the keepers. Some of the later stations used steel or concrete for the tower.


1. Richard Bowman Cohen, "Once There Was Light," Virginia Cavalcade, Vol. 27, No. 1 (Summer 1977), p. 17


DUXBURY LIGHT ("BUG LIGHT") MA, (1871)
CRAIGHILL CHANNEL LOWER RANGE LIGHT, MD (1873)
PENFIELD REEF LIGHT, CT (1874)
SHIP JOHN SHOAL LIGHT, DE (1874)
PORTLAND BREAKWATER LIGHT ("BUG LIGHT"), ME (1875)
SOUTHWEST LEDGE (NEW HAVEN BREAKWATER) LIGHT, CT (1877)
RACE ROCK LIGHT, NY (1879)
GREAT BEDS LIGHT, NJ (1880)
BORDEN FLATS LIGHT, RI (1881)
STAMFORD HARBOR (CHATHAM ROCKS) LIGHT, CT (1882)
BLOODY POINT BAR LIGHT, MD (1882)
SHARPS ISLAND LIGHT, MD (1882)
CONIMICUT SHOAL LIGHT, RI (1883)
TARRYTOWN (KINGSLAND POINT) LIGHT, NY (1883)
SANDY POINT SHOAL LIGHT, MD (1883)
ROBBINS REEF LIGHT, NY (1883)
SAKONNET LIGHT, RI (1884)
LATIMER REEF LIGHT, CT (1884)
DELAWARE BREAKWATER LIGHT, DE (1885)
SAYBROOK BREAKWATER LIGHT, CT (1886)
CUTOFF CHANNEL RANGE FRONT LIGHT, MD (1886)
FOURTEEN FOOT BANK LIGHT, DE (1888)
GOOSE ROCKS LIGHT, ME (1890)
LUBEC CHANNEL LIGHT, ME (1890)
COLD SPRING HARBOR LIGHT, NY (1890)
NEWPORT NEWS MIDDLE GROUND LIGHT, VA (1891)
OLD ORCHARD SHOAL LIGHT, NY (1893)
WOLF TRAP LIGHT, VA (1894)
SOLOMONS LUMP LIGHT, MD (1895)
SPRING POINT LEDGE LIGHT, ME (1897)
SMITH POINT LIGHT, VA (1897)
ROMER SHOAL LIGHT, NY (1898)
BUTLER FLATS LIGHT, MA (1898)
PLUM BEACH LIGHT, RI (1899)
ORIENT POINT LIGHT, NY (1899)
HOG ISLAND SHOAL LIGHT, RI (1901)
WEST BANK (RANGE FRONT) LIGHT, NY (1901)
GREENS LEDGE LIGHT, CT (1902)
HOOPER ISLAND LIGHT, MD (1902)
POINT NO POINT LIGHT, MD (1905)
PECK LEDGE LIGHT, CT (1906)
SABINE BANK LIGHT, TX (1906)
ROCK OF AGES LIGHT, MI (1908)
BALTIMORE LIGHT, MD (1908)
MIAH MAULL SHOAL LIGHT, NJ (1913)
BRANDYWINE SHOAL LIGHT, DE (1914)
THIMBLE SHOAL LIGHT, VA (1914)
HARBOR OF REFUGE (SOUTH) BREAKWATER LIGHT, DE (1926)
FOURTEEN FOOT SHOAL LIGHT, MI (1930)
CLEVELAND EAST LEDGE LIGHT, MA (1943)



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