Just skip Boatswain all together. We did this one through
DCL on our May 8, 2016 Magic Cruise. I did see people in the snorkle lagoon but none had on fins. Its very small and looked shallow. Think of it like a lazy river with some fish. The turtles were ok and it was fun to hold them and get a picture. My mom went in the Aviary and said there were not many species of birds. We ended up spending most of our time in the fresh water pool with our 5yo granddaughter who would have no part of the other activities. If you book through DCL, you will get a "lunch" ticket.... LUNCH IS GROSS! It was bland red beans and rice, plantains, pasta salad (those who eat pasta salad that was not kept cold in the caribbean beware) and the mystery meat was said to be BBQ chicken but the leg bone was very very small, the meat was dark, dry and tasted funny- 1 small nibble and into the trash it all went.... I felt bad wasting food but it was inedible.
If you want snorkeling, I would look into one of the catamaran snorkeling adventures- I think your money will be better spent.
Also one more note, I booked excursions via DCL this time because I wanted the transportation covered and didnt want to worry about running short on $$ and not being able to get a taxi back to the ship but we spent ALOT of time waiting for the group to gather, be sorted, counted, loaded, and sometimes that one group member who didnt listen to instructions to be found... it seemed like a waste of time just to stand around - time that I would have rather spent enjoying the port.