Disagree. Those ships have pretty decent surface radar, they will see any "visitors" coming. Then it's on the radio to call out the calvary, if any Navy has ships or aircraft nearby. Failing that, and most of the time it would, you get on the hailing frequency and warn them off. Then you start shooting, shots across the bow if you feel you can safely do that. Then sink the SoBs, before they can get into RPG or bomb range. If you're lucky you set off their main charge when they're a thousand yards or so off.
Of course the "authorities" in every third world cesspool, and most "first world" ones as well, will defecate a brick if you pull into their port armed with such interesting heavy hardware.
Intersting... sound's like your fimiliar with how ships move at sea which I am not.
But it seems odd that SOP would be to call in aircraft, or the navy becuase another ship came to close. After all the USS Cole didnt, and that thing was bristling with guns and crewed with people that new how to use them.
I dont think the Carnival cruise liner is going to be as on-the-ball as the USS Cole was.