This seems like a silly question, but for snorkeling on Princess Cay to you need to take a boat or can you swim right from shore? I don't do well on boats (so I'm cruising? go ahead, I know you want to say it. <G>) so if I have to take a little one, I don't think we'll be doing it.
Also, having said my problem with small boats, how "rocky" is the yacht cruise to Dunn's River and the semi-sub in Cozumel and Grand Caymen?
(BTW: Its the rocking on the smaller boats that I don't do well with. The feeling that the boat is going to capsize at any minute. Understand the bigger boats (like Sea Princess) do not have that bouncing sensation.)