Draught

Draught (spelled *draft* in American English) is the vertical distance measured from the waterline to the deepest point of a vessel's submerged structure, typically the bottom of the ballast keel or rudder blade. It establishes the minimum water depth required for a yacht to navigate safely without grounding. In nautical terminology, hull draught must be distinguished from the camber or depth of a sail's aerodynamic profile (also termed draft) and from *air draught*, which measures the clearance from the waterline to the masthead.

Draught is expressed in meters or feet. Navigators must account for dynamic changes in draught caused by vessel speed in shallow waters (*squat effect*) and heeling under sail, both of which increase the effective depth of the keel's lowest tip. A structural compromise or loss of a ballast keel dramatically alters draft and stability, as documented in the incident of yacht Polbream.

For large vessels—such as the sail-assisted vessel highlighted in Wikipedia's entry on *Sailing Yacht A*—a substantial draught severely limits access to shallow harbors and coastal passages. Modern captains utilize depth sounders along with technical accessories like those featured in guides for gifts for yachtsmen to monitor under-keel clearance (*UKC*) constantly.