"Airdraft" is how high the top of the mast is above the water. It varies, a little, with draft. When I try to calculate it based on "P", I get about 30 feet. Of cource I want to get under a bridge that is about 30 feet high.

:: Evidently the definition of 'airdraft' is the distance
:: from the surface of the water to the highest point on a
:: vessel