For example, all of Maine down to Cape Small is Intl, and that includes
the Kennebec all the way up to Bath. Harbors such as Block Island ans
Edgartown are Intl, and so on. Admittedly, most of the navigable
channels south from there are Inland, but there are still plenty of Intl
channels, such as all of Alaska.

Now whether a CG boat would actually try to give a ticket to a tall
ship, that's a different question.

So does that mean the US can't keep ships under dither flags out of
those areas because they are International?