What does "under keel clearance" refer to?

"Under keel clearance" specifically refers to the vertical distance between the keel of a ship and the seabed. This measurement is crucial for ensuring that a vessel can navigate safely without grounding, particularly in shallow waters. It takes into account not only the draft of the vessel—the portion of the ship submerged in water—but also additional factors such as tide levels and potential underwater obstructions.

Having adequate under keel clearance is essential for the safe maneuvering of a vessel, especially when considering varying conditions such as changing water levels due to tides or freshwater inflow. Mariners must accurately calculate this clearance to avoid accidents and damage to both the vessel and the seabed.