Drinks and apps at yacht clubs
Try the Dolphin Yacht Club in Marblehead. They are pretty easygoing. They accept CC's. The view is incredible. (If they even ask, you could tell them you just moved to the area and are thinking of joining next year. But I doubt anyone will ask. Just act like you ARE a member!)
Corinthian and Boston Yacht in Marblehead make their facilities open to the public.
In Boston proper, there's Boston Yacht Haven; which has tie ups and is close to Joe's, Sail Loft and the NE.
Fan Pier is convenient to the Seaport District.
Neither of the Boston proper marinas are private, though BYH has a nice clubhouse that is available to renters. Nice big room with a pool table, big screen TV's, internet access, workout room.