Short review for people debating wether or not reading this but the reviews available are almost as long as the manga itself:
It's not good. The premise is zombies and teens on a ship, but the plot is weak, the art style is weird, the pacing is kinda messed up and the characters can be either good or unbearable, there's no middle point. You can find weird ecchi scenes scattered thoughout very tense moments, ruinning the latters. I do not recommend this if you're looking for some quality stoy-telling. If you don't mind any of that and just want something to read or really love people wetting their pants, go ahead.