UKC (Under Keel Clearance)

Under-keel clearance is the vertical distance between the lowest point of a ship’s keel and the seabed at any instant. The static figure from charted depth, tide, and draft is reduced underway by squat, by heel and by the change of water density in brackish or fresh water, and is further eroded by wave-induced heave and pitch in a seaway. Port authorities and company passage plans set a minimum UKC, often expressed as a percentage of draft, and the master plans tidal windows so the planned UKC is never breached over the shallowest leg.