Under keel clearance
In seafaring, under keel clearance (UKC) is the vertical distance between seabed and the keel or hull of a ship. It is used to ensure sufficient navigable water is available for ships at sea. Master mariners should ensure there is sufficient minimum UKC for their ships; ports should ensure sufficient minimum UKC for the type and draft of ships due to arrive in the port. Ships typically calculate their UKC to meet criteria for ports to minimise the risk of maritime incidents. The minimum UKC determined includes a safety margin.