You should consider how much boring that big hole would weaken the deck right beside the mast step. If this could be a problem, perhaps you could modify the mast step by lengthening the plate at the bottom of the mast a bit, as well as the piece bolted to the deck. IOW, make the hinge a little longer so there will be no contact. Easy to spend someone else's money!
I remove water from wood with a little douse of denatured alcohol. Seems to, anyway.