The mentioned 12 mile ‘Boundary’ is only in the GOM. Reading that cite, it says, 12 miles in the GOM, and 3 miles on East and West coasts. I have seen the MSO Providence boundary line chart (that they use to determine on a quick, visual basis) and their ‘boundary line’ runs from Montauk, to Marthas Vineyard, to Nantucket, then to Chatham, along the shore to Provincetown, then in a straight line to the B Buoy (Boston), then to Cape Ann. There is little resembling a 3 or even a 12 mile contour in this one!
Once while I was running a ferry from Nantucket, I had to over take a vessel in the narrow channel. I blew the appropriate blast to overtake, in a narrow channel, international. The guy called me up in the radio, and asked why I was blowing an international signal in Inland waters. Two separate issues. We were in International RR territory, but in ‘inland’ license territory.
The boundary line does not even exist between Delaware bay and NYC. It is impossible to be inland, while outside the sea buoy in this area. Actually this in not true, the three mile boundary exists, it just cant be complied with, without running aground at the mouth of the Delaware.
Barges that have to load deep, (over the special service marks) to get the maximum amount of cargo on, cannot go to sea from the Delaware Bay, to New York. BUT, an overloaded barge can traverse from NY to Portland, ME via the inside route, and be totally over the marks! Go figure! And we thought ABS was the sure fire way to be safe!