I am not following this thread. I used to do one and two day cruises to nowhere out of Manhattan all the time in the early 2000's and it was not a violation of Passenger Vessel Services Act. I did a few bachelor parties back then, four to a cabin we never visited other to get out of a bathing suits when the pool closed.
Wasn't CTN's banned due to some employee tax issue for gambling day cruises and daily Bahama cruises out of Florida, claiming the employers did not have to by income tax even though employees on the were in the US every day .
All the mass market cruise lines did CDN's to get back on their rotation schedule when coming to NY for a season.