I don't know the technical term for it, but some people actually have told me a thing exists where people board cruise ships from the middle of the sea without paying.
Given that there's no jail/confinement facility on these ships and the company will probably not cancel a whole trip just to take one buffoon back to the land and arrest them, ruining everyone's paid trip/jobs/etc.
Would such an act even be illegal? Would they maybe just restrict the hopper from any events/amenities and make them stay out port? I ask because somethings like this are probably rare, but totally possible, especially with massive cruise lines where you may be likelier to go unnoticed and get off easier too.
Even if the cruise line did tell the authorities, it's not like boat police are always present, especially if the ship is near international waters/boundaries/not in one specific geological region/etc.
I'd imagine that even if someone did get caught doing this, or if they actually did enforce this rather than simply forget about the hopper, punishment would be very minimal/petty.