First maybe you need to be clear on US registrations. There are two different types of "registration" for a boat in the US.
1. A boat registered with the US government
through the US Coast Guard is correctly called a "documented" vessel. And US law does not allow a foreign citizen to document a boat. There are discussions about setting up a US corporation that is owned by a non US citizen to own and document the boat but that can be complex, expensive and I will not try to advise on the details of doing this.
2. A boat can be registered in a state, California, Florida
, etc. I do not know of any states that forbid registration
by an non citizen and in fact most states do not care if you even live in the state. In fact many states will require an owner to register the boat in that state no matter where the owner lives, if the boat stays in that state more than 90 days.
One further note, a US citizen may have a USCG documented boat and also be required by a state to register as well. This is mainly a tax and revenue issue by the state and in no way changes the USCG documentation
. But a boat that is state registered does not have to be USCG documented, even if owned by a US citizen.
There is no requirement for a boat to be USCG documented so if you plan to buy a vessel that is already documented by the US owner the documentation can be canceled and you can own the vessel with no problem. However, unless you can then show some form of registration overseas the state where the boat is docked will probably require registration in that state. The process is usually simple and relatively inexpensive. In FL maybe $100-$300 depending on the value of the boat. The states just want your money
and make the process very easy.
Not sure why you were told that it is difficult to buy a boat in FL as a non citizen. I used to be a yacht broker in FL and I know of no impediments to sales to UK citizens. You will have to be aware of regulations
that might require you to pay a 6% sales tax if the boat stays in FL too long but that process is clearly defined and easy to comply with.
Of course none of this addresses issues with visas, registration of the boat in the UK or other country, etc. In that area I can't help at all.