A two-hour tour

After today's Maritime History Cruise you'll know so much about Boston Harbor that you might want to start your own tours - just stay away from the name "duck." Experts on Boston history will discuss the changing topography of the Harbor, British troops on Long Wharf in 1768, the battle of Chelsea Creek, shipbuilding in East Boston, military defense on Long Island, and Fort Independence. Today's know-it-alls include Robert Allison, chair of the History Department at Suffolk, and Nancy Seasholes (it's really her name), author of "Gaining Ground: A History of Landmaking in Boston." The two-hour tour boards at Rowes Wharf at 1:30, rain or shine. 2-4 p.m. Free. Reservations are required at 617-482-1722 or mail@tbha.org.tbha.org