 At that stage, the southern outlet of the Moyne, the Back Passage, was narrow and the opening to the sea was often too rough for boats to leave or enter the port; the main eastern outlet was blocked by a shallow sand bar.These navigational impediments led to the construction of a jetty from Flagstaff Hill and a boulder wall breakwater between Griffiths Island and Rabbit Island.Training walls constructed in the 1870s curve from the northern part of Griffiths Island through the sand bar.