Air draft is the vertical height of a boat measured from the waterline to its highest fixed point. For a superyacht tender it is the dimension that most often binds the garage: a hardtop or limousine cabin sets the height, and the headliner must clear the door track with the cradle raised.
It is routinely underestimated because brochures quote it off the cradle rather than at launch clearance. The tender garage sizing guide covers how it is actually measured.