"I understand from a mate of mine who's much given to going on cruises that certain cruise companies insist on frisking your bags every time you re-board the ship in case you're trying to smuggle onboard the cheap booze that you bought onshore, presumably to force you to buy the grossly-overpriced stuff they sell onboard."

So it would have nothing whatsoever to do with International Maritime Organisation ISPS Code 2003 requirements then.