In nautical engineering, air draft refers to the height of a vessel above the waterline. It is typically measured from the waterline to the highest point on the vessel, such as the top of the mast or the highest point on a bridge. Air draft is an important consideration for vessels that need to pass under bridges, power lines, or other structures with height restrictions. The air draft of a vessel will determine whether it can safely navigate through these obstacles without the risk of collision or damage to the vessel.