First you take a taxi to Red Hook, the ferry and then once at St. John another taxi to a beach. There is a ferry schedule, I think its once an hour, same with the way back. So, you need to allow plent of travel time, but well worth it IMHO.
First of all St. Johns is the place to go if you go to St. Thomas after you get the beaches of St. Thomas out of your system. So the next quesion is how do you get to Red Hook, There is a ferry that leaves from the downtown pier. It was operating about twice a day. If you can find out when it operates and it matches your schedule utilize it. When you come back from St. Johns it is the most direct and cheapest form of transport. Watch your time since you have to get back before ship departure and the ferry will meet these objectives.
This was proven to me after riding the ferry back. I returned to the cruise ship after shopping in town I rode the dolla taxi to the port. My friends who had traveled with me on the ferry were sitting on the porch of bar enjoying a beer. In other words there was plenty of time to get to ship.
If don't take the cruise from St. Johns to St. Thomas. You will have to get the local ferry over to Red Hook and get a taxi back to the port. You are at the mercy of the taxi driver on this run which may cost you as little as $20 for the ride to
Red Hook, but a lot more for a speedy ride to the port.
Also when you buy a ferry ticket you don't necessarily want to buy a round trip one. You may want to buy one from Red Hook to St. Johns and then buy another from St. Johns to St. Thomas.
There is always Meagans Bay in St. Thomas if you want a nice beach, but no snorkeling there. Nice calm water and white sand beach. A short taxi ride from the pier, especially if you have not been there before.. You can also shop downtown or just shop at the pier, they have the same shops as downtown, but right next to the pier.
Megan is great and one of the most beautiful beach in the world. You have to get there via taxi because it is on other side of island. Brewers beach by the airport is on the same side of island as the ship docks but lacks facilities. It like most beaches on St. Thomas is beautiful and very well kept.
Megan's is beautiful - I think the taxi was about $12/pp each way plus and admission fee, but I may be wrong there - 2008 was the last time we were there
Carnival does have a snorkeling excursion to Trunk Bay on St. John (I think) if you are more comfortable doing cruise line excursions. If you have not done so already, create an account on the Carnival website, enter your booking number and you can see information on all the excursions on your cruise. You can even book them if you are concerned about something you really want to do filling up.
Carnival encourages the pre-booking so they can do capacity planning. Of course you have to pay at the time of booking as well so they get a couple of bucks early.
A Bad Day At Sea [with power] Always Beats A Good Day At Work
Coral Princess - tour starts 5/31 in Fairbanks
There are plenty of great beaches in St. Maarten. Mullet Bay is fantastic if you are there during the week because the beach isn't crowded at all and the water is just unbelievable. You can order ribs etc... on the beach too.
Another great beach is Tintamarre island, a small island just off St. Maarten on the French side. That place is just amazing too. You will have to use an excursion to get there... Last time I was in St. Maarten, we used the Golden Eagle Catamaran tour to get to Tintamarre. The tour was great! It lasted four hours and we were back on island for the other half of the day.
A good website to get info on the beaches on the island and the various tours is www.sxmdeals.com.