Vessel & Tonnage

Air Draught

The vertical distance from the waterline to the highest point of the ship — what must clear under bridges and cranes.

Air draught is the height of a vessel above the water: from the waterline to the top of the mast or other highest fixed point. It changes with loading, since a more laden ship sits lower.

It is the critical clearance figure for passing under bridges, power lines and gantry cranes; an under-estimated air draught is a recurring cause of bridge allisions.

Also known as: air draft, overhead clearance.

Related terms

Draught

The vertical distance from the waterline to the bottom of the keel — how deep the ship sits in the water.

Load Line

The marks on a ship’s hull showing the maximum permitted loading draught for different water densities and seasons.

Plain-English reference definition — our own explanation of a standard shipping concept, not a licensed source or legal advice. See the full glossary or the broader maritime dictionary.

Last reviewed: June 2026.