I've been on a cruise to the Bahamas and elsewhere, but it was Holland America. I'm pretty sure they all use the same approach. You sign up in advance for different activities in each port. If you choose scuba, the cruiseline already has a contract with a particular op. If you sign up this way, I assume that the op knows the ship's departure schedule pretty well. Usually, if you are in port just for the day(at least in Nassau), this means you will do the morning dive series. Of course, if you are adventurous, you can make advanced reservations with a dive op yourself and they will pick you up at the dock. Regarding Coco Cay-- I have not been there, but it is probably just like the 'private islands' that the other cruise ships use. Crescent Key, Half Moon Cay... you get the picture. The diving at these spots won't be that great for the price, but hey--its diving. Very popular dive ops on Nassau include Nassau Scuba Centre and Stuart Cove's. Stuart is a 'mega shop' and NSC is smaller. I prefer NSC myself. Happy diving!