I know that during my drinking days, while I still had a modicum of control when I really NEEDED to have it (though I could never manage it for too long), any time I kept the drinking on a "short leash" there would be this boomerang effect, where I basically did "make-up drinking" to compensate for how I'd been depriving myself. Sort of the way a person will binge after being on a strict diet.
I don't think he is going to have a gentlemanly aperitif, a glass of wine with dinner, and civilized nightcap. He is likely to be drinking his brains out because he's giving himself permission to let loose.
And even though there are a lot of people around on a cruise ship, that doesn't make it a safe place. If you look around online there have been many incidents of DV on cruise ships. There's very little opportunity to get away from him even if you need to.