#91191
IMG 1724PaulK
Participant

Looking at the drawing of the Cal 30 here on Sailboatdata will help you.  The Mark I listing gives the dimensions for P and E, for example.  P is the height of the mainsail from the boom to the black band at the head. E is the length of the mainsail on the boom. If you mark the distance from the boom to the waterline on a piece of scrap paper you will find that it is about half the length of the boom. That means that the boom is about 7′ up from the waterline. Adding the P dimension of 30′  gives you a rough air draft of 37′.  Maybe add two feet for the actual masthead casting, wind instruments and antenae, and you get 39′.