“Safe” is a relative term.
First and foremost, we are assuming that the personnel aboard the vehicle in question are able and willing to work with one another. On a submarine or military vessel of some kind – even some merchant marine vessels – this would be a reasonable assumption.
Aboard a cruise ship, I dunno. What’s the likelihood of several hundred civilians allovasudden not being able to go home and shutting up and doing as they’re told, even as the food is suddenly rationed, and they’re put to work, doing chores the Captain deems necessary to the survival of the whole? Hell, I think once the news got out, the Love Boat would become the Pandemonium Princess.
Crews aboard oil rigs would be safe for a time, but there’s the matter of resupply. Eventually, they’d have to worry about scurvy.
In the original DOTD, news broadcasts carried on for quite some time. Eventually, they quit. Isolated survivor groups on ships would be able to gather the information necessary to their survival, and take steps. In the remake, on the other hand, all we see is total insanity bursting loose, followed by the complete shutdown of all media within 72 hours of the outbreak. How much information could get through? These poor schmucks on the boat may not even know how the disease is transmitted… and that’s if it’s a disease. Keep in mind that even if naval officers normally carried small arms around everywhere they went, how willing would they be to shoot their crew, even if they were acting weird and crazy? By the time the crew figured out what caused the disease, half the freakin’ crew could have been bit… and that may well signal the end for the other half, don’cha think?
In the original DOTD, anyone who died for any reason came back as a zombie. This would pretty much mean the total infection of every island and landmass, no matter how small or large. In the new version, though, only zombie bites caused new zombies… so, theoretically, any isolated landmass could escape infection, provided they immediately quarantined themselves and shot down any incoming aircraft, and sank any incoming boats. England’s too close to Europe – they’d be screwed – and Australia’s too frinkin’ big – but New Zealand might have a chance, as would any number of small inhabited islands worldwide. Hawaii. The Turks and Caicos. Even Guam and suchlike.
Next, we introduce the matter of pirates. Seems like a boatload of armed guys who found themselves running low on certain essentials may well find this a viable option for obtaining them with a minimum of expense.
I propose a theoretical fight between the Revenge (formerly a Naval ship of irrelevant origin) vs. a Princess cruise liner. Who wins?
Again, it depends on your definition of “safe.” The George Romero zombie movies always made it VERY clear that the LIVE folks were the REAL monsters…