The particular site of Immingham was chosen because the deep-water channel of the Humber, which lower down runs midway between the shores, here makes an inward sweep and leads right to the dock gates, thus obviating much initial dredging, providing ingress and egress at any state of the tide, and rendering the towage of the vessels unnecessary.
The mean depth over this ridge is about 250 fathoms, and the maximum depth nowhere reaches 500 fathoms. The main basin of the Atlantic is thus cut off from the Arctic basin, with which the area north of the ridge has complete deep-water communication.
Casilda (pop. in 1907, 1246) has a landlocked, shallow harbour; but Masio Bay, a trifle farther distant, accommodates larger craft; and there are excellent deep-water anchorages among the quays off the coast.
In many cases a still heavier type is used for the first mile or two from shore, and several intermediate types are often introduced, tapering gradually to the thin deep-water type.
To vessels of the largest draught, and there is sufficient deep-water anchorage inside for the navies of the world.
Associated with this dock was the construction of adjacent deep-water wharf walls, together with the great 160-ton crane.
A breakwater was therefore planned on the Monarch shoal, to double the available anchorage area and increase the frontage of deep-water wharves available in all weathers.