The Crow Stone marks the limit of the Port of London Authority's jurisdiction. The line, known as the Yantlet Line, between the Crow Stone and the London Stone, Yantlet Creek, almost due south on the other bank of the Thames is used as the eastern boundary of the jurisdiction of the Port of London Authority.
I also wanted to include a Thames sailing barge, common on the River Thames in London in the 19th century. The flat-bottomed barges were perfectly adapted to the Thames Estuary, with its shallow waters and narrow rivers.