Okay, fine, I can't resist...it might be tempting to take a big ole cruise ship out to the middle of San Francisco Bay and just park there, but has anyone considered that decaying bodies float? I'm not at all convinced that the whole zombies-can't-swim philosophy is something I'd stake my life on.
Not to mention that if someone in your party died of natural causes, you'd still be stuck with a zombie on the ship, and who knows if you'd be able to get to them in time. Especially on a really big ship with a lot of people, and a lot of hiding places.