It's fairly simple to get CG Documentation; since the boat was previously documented. Just file a change of ownership with USCG; pay the $100 processing fee and pick a new name. You must be a US Citizen to own a USCG documented vessel. There is no annual fee for documentation; but you probably will get a Property Tax bill from your county instead of the similar DMV fee on your Registration.
Forms are here:
USCG National Vessel Documentation Center, Forms Page