Are you looking at a 'trip' over to Europe and then bringing it back, or, taking it over and leaving it there whilst you 'commute', or will you be living permanently aboard ?
What sort of boat is it (make / model) ?
What age is the boat ?
Europe is extremely 'hot' on RCD paperwork has it got a certificate of compliance ?
Does it have the certificate of location dated/timed Dec 31st 2020 at 11:00 pm which is when we finally left the EU
You will almost certainly need a certificate of payment of VAT
Depending on which country(s) you plan on cruising there may well be Radio (Marine VHF) licence requirements for the boat and the operator.
Black water holding tank ?
Your qualifications ?
It is bad enough having the correct 'paperwork' for just a short couple of days visit.
Join the RYA or DBA for up to date specific country information