Under Keel Clearance (UKC)

Under Keel Clearance is the vertical distance between the ship's deepest point + the seabed. Company + charter-party + port-authority policy sets minimum UKC — commonly 10-30% of draft in open water, higher (~15%) in transit channels, terminal-specific in port. UKC calculation must include squat + heel + wave allowance + tide + swell + hydrographic uncertainty. Under-keel-clearance policy failures + misjudged squat are among the top-3 grounding-casualty causes.