The restorations extend the life of the nearly 2-feet (61-centimeter) -thick vessel — the last remaining survivor of six ships created when President George Washington signed the Naval Armament Act — said Margherita Desy, a historian at Naval History & Heritage Command Detachment Boston. The most recent work included replacing 100 hull planks and installing 2,200 new copper sheets, 500 of which were signed by nearly 100,000 museum visitors, according to USS Constitution Museum President Anne Grimes Rand, who called the ship "a wonderful symbol for our democracy." The Constitution entered the dock at the historic Charlestown Navy Yard on the night of May 18, 2015, and on Sunday — a day expected to have the highest tide of the summer —the dry dock at the navy yard will be flooded, and the ship will be lifted off the keel block that night.