"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