We have a Ferry nearby...at the Port of Rochester, NY. It does not fly under the US Flag and there is a fee involved on a daily basis. I believe also that the ships mates are not and do not have to be UNION because they are not flying under the US Flag. My brother could explain it better, He's a Captain.
I'm no expert on this topic. All I know is what I saw on TV. The point made was because cruise ships are not registered in the US then they are not subject to US laws.