OK, I know you don't want to spend a long time getting somewhere. But the most spectacular snorkeling is towards the south of the island, and getting there is incredibly beautiful. If your ship offers a sailboat or catamaran cruise to Soufriere or Anse Chastanet, go for it. You'll get to see the rugged coastline and the Pitons from the water. You'll feel like you're in Hawaii. Anse Chastanet is unbelievable, and I've gone diving there and snorkeling there many times, and I'd go again tomorrow!! There also is/was a tour where you sail to Soufriere, go to the "drive-through" volcano, see the sulphur springs, eat lunch at a local place overlooking the Pitons, and make 2 snorkeling stops. It was relaxing and so beautiful! Have a great trip!
Lorri