After five pages and over 100 responses, it is clear that your son's fears, while very real to him, are what the majority of respondents would call irrational. Having said that, if he is that concerned, there is no way he should consider going on this cruise. He will be constantly on edge, fearful of what's lurking in the sea at night, jumping at every unexpected noise or bump in the ocean. And heaven forbid...a lack of hash browns. A cruise should be a time of relaxation...not trepidation.
I'm not a psychologist, and unlike Bob Newhart I don't play one on TV...but in my totally unprofessional opinion, your son is better off on dry land where apparently he feels "safe".