With out the boat you are concerned about, the next best is to make educated guesses.
Using the data available from Sailboat Data
The C&C 40-2 is a completely different design from the earlier C&C 40. A keel/centerboard model was also offered. Disp: 17985 lbs./8157 kg. Ballast: 8795 lbs./3989 kg. BU: 4.75’/1.45m BD: 8.5’/2.59m Deeper Keel: 7.5’/2.29m TALL RIG: I: 55.00’/16.76m J: 16.60’/5.06m P: 48.50’/14.78m E: 13.30’/...
sailboatdata.com
The mast from the level of the boom to the top of the mast…
Tall boat 49 ft. Or a standard boat 47 ft.
Estimating the height from the water to the level of the boom could be 5-7 ft.
Being conservative in this case, a reasonable number might be 63-65 ft. I suspect this number is overstated. You can use it to slip under a bridge. Likely you will actually measure the Airdraft before you power up towards the bridge.