There were two entrance to Basin 5, the Prince of Wales Basin, one of which was through the North Lock.

This Lock, which could also serve as a Graving Dock, was 730 feet in length and 121 feet in width, although the maximum widths at the entrances was 95 feet at the coping.  Caisson K at the Hamoaze end, and Caisson Q at the Basin end both slid into the side walls.  Floating Caissons could also be used against the outer stops, which would lengthen the Dock to 787 feet.  The walls at the entrances had a batter of 1 in 12, rounded off with a radius of 5 feet at the sill.  The depth of water over the sill was 32 feet at low water spring tides and 47 feet 6 inches at high water.

The foundations of the wall enclosing the dock, as well as of the sill and the floor, were carried down rock.  The wall itself was constructed of concrete faced with granite.  The upper altars and the top vertical walls were of granolithic concrete blocks with granite coping.  The height from sill to the coping was 55 feet.

At high water, or when the Lock is already occupied by a ship, the second entrance direct off the Hamoaze could be used to enter the Basin.  Caisson R could also slide in to the dock wall.  Like the other entrances, it was  95 feet wide at coping level and 47 feet 6 inches over the sill at high water spring tides.

Just to the south of the Caisson K entrance was Wharf Number 4.

To the east of North Lock were Dock 10, Dock 9, and Dock 8.