The original entrance to the docks is wide, with two wrought-iron gates operated by direct-acting hydraulic cylinders. This sea entrance leads into the Basin (occasionally called No.3 dock), that is and covers . At its northwest end, the Basin is connected to No.1 dock by an wide passage with another pair of wrought-iron lock gates, so that when required, the Basin can act as a lock, with the water level adjusted according to the rising tide. This enables wide-beamed vessels to leave the basin before high water and to enter the basin after high water.
