Before dry docks came into use in the late 15th century in England, the only way to service a ship’s hull was to “careen” it—heave it over on its side, still floating, or laying in the mud at low tide. It was difficult and time consuming and put great strain on the hull. The answer was the dry dock. The concept is simple: float the vessel into a three-sided basin, then close the seaward end and remove all the water. The vessel settles on a cradle, its hull accessible. To undock: re-flood the basin, open the seaward end and float the vessel out.
But the concept’s execution required a finely-engineered complex of masonry, engines, pumps, reservoir, tunnels, culverts, valves, and gates—in effect a huge well-coordinated machine. The Charlestown dry dock and the one built concurrently at Norfolk, Virginia, both designed by Loammi Baldwin Jr., were the first such naval structures in the United States. Six years under construction, the Charlestown dock was inaugurated in 1833 with the docking of Constitution. Over the course of its history Dry Dock #1 has been enlarged several times. In 1833, the dock was 341 feet; in 1858–1860 the dock was extended to 357 feet. The final extension occurred in 1947–1948, when the dock became 415 feet in overall length, the size that it is today.
It took the original eight pumps 4–5 hours to empty the tremendous basin. Other operations were to some extent governed by Boston Harbor’s 10-foot tide. After the dock was enlarged, the water level did not rise as rapidly as the tide during filling, so it took two high tides to do the job. For emptying and filling, the caisson (door) was filled with water and sunk in place between grooves in the dock walls. For docking and undocking, the caisson was emptied and floated out of the way on the high tide. It took 24 men working hand pumps for an hour and a half to expel the water from the caisson.
The original 1833 wooden caisson was replaced with a riveted steel gate that was launched October 31, 1901, and placed in service in 1902. Dry Dock #1 had its third caisson installed on April 1, 2015. The new caisson, built by Steel America in Norfolk, Virginia, weighs 296 tons and was launched from its barge into Boston Harbor by “Chesapeake 1000,” the largest East Coast floating crane that is capable of lifting 1,000 tons.
Charlestown Navy Yard is part of Boston National Historical Park, one of 407 parks in the National Park System. Visit www.nps.gov to learn more about parks and National Park Service programs.
Boston National Historical Park is a unique collaboration of government owned and privately owned and operated historic sites associated with the colonial struggle for independence and the birth and growth of the United States. These nationally significant attractions include Old South Meeting House, the Old State House, Faneuil Hall, Old North Church, the Paul Revere House, the Bunker Hill Monument, the Bunker Hill Museum, Dorchester Heights Monument, and the Charlestown Navy Yard, including USS Constitution, the USS Constitution Museum, and USS Cassin Young.