Well, maritime law doesn't necessarily supplant state law, particularly on the criminal side of things.
And I know the Coast Guard takes the position with commercial vessels that being made fast to a dock, or sitting at an anchorage doesn't exempt the master from federal charges for being drunk while "in charge of a vessel". The theory here is that one might have to get underway at any time if there's a change of circumstances or an emergency.
I don't know the law or have any first hand experience with precedent in this area...but if cited for BUI when at anchor I would get a lawyer and fight the charges.
It doesn't pass the commons sense test to me that one can be cited for BUI while anchored when - while anchored - one could have easily taken the dinghy to the beach and not been on board when the LEO arrived at the boat and - I guess - not be cited for BUI.
It also doesn't pass the common sense test to be cited for BUI while anchored but not be cited when alongside in a marina...or tied to a mooring ball. Could I be cited for being drunk in the cockpit while tied in my slip but perhaps not be in violation if I am standing on the finger pier next to the boat?
I have never seen LEOs surround the holiday weekend raft ups with citation pad in hand although surely they know - like the rest of living and breathing society - that the majority of the of-age crews are likely a bit deep into their cups.
nola: Re CG "takes the position" - by what authority? CG can't simply take a position independent of law or regulation. What regulation is cited in taking the position that a master of a commercial vessel must exercise sobriety at all times?
What if the ship is in dry dock? Steam powered and in cold iron conditions? Not ready for sea due to crew leave? Is at anchor but has a system fault that prevents getting underway safely?
When I consider all the irrational actions by persons of authority in schools and LE agencies that have been highlighted in the media in the past couple of years I shouldn't be surprised that the CG and marine police have gone off the deep end regarding BUI.
All it takes is a Little Napoleon or Mayor Bloomberg ego on the LE vessel to make a wonderful day on the water become frustrating.