Take a cab to Dickenson Beach. Been twice and great.
Sandals has the resort there so that should say something about the water.
We went to Shiggity shack which is on abeach but not that impressed with the texture of the sand. My suggestion would be to go the Marriot hotel.
NO beaches to my knowledge as have been twice. Known for Rain Forest activities and whale watching. BOTH extremly great excursions. Whale watching will be booked through ship due to limited vendors but others can be booked at the pier for tours.
Have done the Silver Moon Cat excursion twice. Book through Ocean Adventutes. Last time we went to the boatyard which was a blast. Short cab ride, 15 to get in which gets you a lounge, drink and cab back. Don't let cab talk you out of it as they get pieced off for dropping elsewhere.
Hope this hlps and ask away for further info.