What is meaning of Air Draft Or Air Drought Of Ships?

Safety air drought (SAD)

Air drought is distance over ship, when manoeuvre under construction. They mainly consist:

1. Bridges (road, railway) over waterway .
2. High voltage lines,
3. Pipelines over waterway,

The condition of safety ship movement is following.

 H_S  < H_C

Where :

HS =  the height of highest point of ship and
HC =   the height of lowest point of construction over waterway.

Note :

• In many cases, the sea-river ship’s superstructure is regulated. It permits to decrease of ships height. Also other elements of ship’s construction can be disassembled – for instance masts of radar antenna, radio etc.