FWIW, My wife and I just came back from two weeks on Cozumel, and we spent every SI on the boat. We encountered none of the inconveniences of which you speak. To each his own (and neither of us are prone to seasickness), but SI's on the boat are fine with me.An hour in close corridors with a stand up urinator, the chain smoker, the guy who never shuts up about his dive history etc. etc. can be miserable.