We traveled to the Buck island to snorkel and swim with the turtles. I went on a sailboat. You can sit on the front of the sailboat but you will get wet there for sure when the waves hit. The morning was foggy and a bit rainy. But by the time we got to the island the weather was clearing up. The water is very clear and you can see down about 30 feet down to see the turtles eating at the bottom. They do need to come up for air from time to time so you can get a even better look. On the way back they offered rum punch, pop and water. A worth while activity. Since I had been to Megan beach before I chose this to do something different. But if it is your first time and you have time at the port you should do both.
I chose to do a tour of both the Dutch side and the French side of the island. To tell you the truth other than one side using more colored paint on their buildings then the other i didn't notice all that much difference. The tour guide was quite boring actually pointing out the local fire stations, Mc Donalds and KFC. I can see those at home not a highlight for me. He also took us to a small zoo that was not on our itinerary. I figured he must of wanted to give a kickback to a relative and they collected donations to see iguanas and donkeys. I wish I had just gone to the Orient beach and Sunset beach only. We did stop at one shop in the port area. It had guava berry rum. It was really good I suggest you get a free sample to see what you think. I think they only sell it here.
Oh by the way when I got back my boss sent me an article saying mosquiotes in St Martin are carrying a virus. http://www.cbc.ca/news/health/mosquito-borne-health-alerts-issued-for-st-martin-1.2470221 We did see some flying around. You might want to wear insect repellent.