We went through Sebago in December, very small crowd (only 17 of us) on the catamaran which actually was great. Felt like we had the boat to ourselves. The captain of the ship acted and talked like robot. I understand safety talks and such but he was pretty uptight and condescending to the rest of his deck mates and spoke down to some of the customers which made him look like a fool. He was obviously annoyed by certain people and had little patience. The crew, other than the captain, was great and made small talk with us the whole way.
Snorkeling was the best Ive ever done or seen - water was super clear and there was SO many types of creatures to see. Unfortunately both me and my daughter were stung a few times by jellyfish so that quickly ended our time in the water.
We saw another catamaran near us with snorkelers from a separate tour. Two of their people couldn't swim and drifted towards our boat so they had to do a water rescue for them. It was pretty ridiculous and entertaining to see - no fault of our tour at all. IF YOU CANT SWIM DO NOT GO SNORKELING. You are literally miles from the shore in 20 ft water with a decent current.
Free beer on the way back was great and the ship itself was comfortable and relaxing. Overall I'd do it again for sure.