This was a once in a lifetime experience! I've never been snorkelling before but the crew made it easy - they had flippers of various sizes, they had de-fogging spray for the snorkels (which are sanitized between uses), they had yellow inflatable vests that you could choose how much to inflate, i.e. can help you float so you can spend time gazing instead of treading water. For those who were less comfortable with swimming they even had pool noodles available, and it felt very safe as they had a spotter on the boat, and another person with a life board swimming around us in case anyone had trouble (no one did).
Captain Patrick and his crew were all friendly and could answer any question we had about the aquatic life. There was also a professional photographer, Adam, on board to take pictures during the cruise and even underwater during the snorkelling, and sell a photo package afterwards (I usually never buy a photo package, but this was worth it).
Our cruise was very great - we saw whales on the way out, dolphins on the way back, and a sea turtle and numerous tropical fish while snorkelling. some of that is due to luck, but also to the captain and crew's experience of knowing where to go, when. The food was good too, they had a lot of drink options and even had sunscreen lotion available.