I am trying to find a statewide list of boat owner registrations in
the state of CT, all with addresses and sortable.

I doubt that the Connecticut Department of Motor Vehicles (competent
for registration of motor-powered watercraft) will make this kind of
confidential data available. I'd say that there is no legal way to
obtain such a database.

Scriptor

If you need to find the owner of a particular boat that you have the
registration number of, to lodge a complaint or return lost goods, or
similar, just advise the registering authority and let them contact
the owner . If its lost goods, leave your phone number with the
authority and they can pass it on to the owner. Their data base is
then protected as they have not divulged the owners details to you,
but the owner is able to contact you. It worked for me..