malcom,
1) i have recently bought a boat in the u.s. and, yes, you have to take it off the uscg registry (only american citizens or permanent residents or corporations with similar majority
ownership can own a u.s. flagged vessel). this is not a big deal and i reflagged in jersey (which was simple and cheap)
Welcome to Jersey Harbours
2) i'm not sure you need any particular cert of competence (or skipper's ticket). you can go to
BoatingBasicsOnline (change state to suit), do a very simple on-line course, get a cert and this is recognised by the uscg
3) uk citizens can enter the u.s. under the visa waiver scheme which gives you 90 days. longer than that and i guess you'll need a visa. i'm a new zealander and it works the same way for us.
4) once the vessel is uk flagged your
radio will need to be licensed by the uk
regulator "ofcom"
Home page | Ofcom (it's a bit similar to the "u.s. citizen-boat
ownership deal")
bob