The height from the waterline to the highest point of the vessel
The distance from the vessel’s water line to the uppermost point on the vessel, usually the top of a mast or radar tower. When a vessel has to transit areas where there may be overhead obstructions (bridges, power
lines, cranes, loading arms, etc.) it is vital to know what its air draft (draught) will be at the time of transit. The air draft of a vessel will
vary depending upon the draft of the vessel and its trim.