How does the draft of a ship affect the cost of building a berth?

In the field of civil engineering for harbors and sea works, the capital cost of building a berth is significantly influenced by the depth of the water required to accommodate a ship's draft.

It is estimated that the capital cost of such berthing works increases roughly in proportion to the cube of the deepest draft of the ship the facility is designed to accommodate. Because modern vessels, particularly large ones, risk serious structural strain if they contact the seabed, engineers must ensure the berth is adjacent to water deep enough to float the vessel safely.1

This relationship creates a major economic challenge as ship sizes increase. For example, if the formula relating capital costs to the deepest draft were applied to modern supertankers—which can draw up to 72 feet of water—the cost of building a conventional berth could be more than six times the cost of a berth designed for a vessel with a shallower draft, such as the 42-foot draft of the Queen Mary. To mitigate these costs, engineers often site bulk terminals further out in deep water, using lighter structures like piers or jetties rather than traditional, expensive quay walls.2