Golden Eagle Catamaran in St. Maarten and pretty much any excursion to St. John that includes snorkeling is great.
FYI, the French beaches in St. Maarten are European style and probably will have nudity of some type. If this is a concern for you, you might choose to book excursions to Dutch beaches.
Contrary to popular opinion, I think it takes too long to get to St. John for an excursion. We take a taxi to Sapphire Bay and rent snorkel gear there. Reefs are very close to shore and there's an outdoor poolside cafe for lunch. Other water sports are available, too.
My vote again for Captain Nautica! They seem to be the best and are so freindly when I call them! I am having to coordinate booking them separately from DCL because of the age limit (>8 y.o)....we have a 6 yo and I am in the midst of booking them so we can go. Parker, the owner, is very nice and professional. Just go to their website to learn more.
I will second that everything I have researched about the "ferry boat" to St. John's Trunk Bay is tooooooo long and boring. Especially with kids.....you ought to research Captain Nautica's speed boats!
We did the St. John trunk bay snorkel excursion and loved it. It is so beautiful there. I think it took about 45 min to 1 hr on the ferry, but was a nice trip. It is a short bus ride (very scenic) to the bay. Trunk bay is just the most beautiful beach I have ever seen. It is like the jungle coming right down to a sandy beach. There are signs along the snorkel trail explaining the sights. It also had a lifeguard on the beach and in a kyak. There are also showers and place to change for the trip back.
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