Keys
I doubt you'll find on this forum which is principally a sailing forum a boat to buddy with. However, if you are going to the Isthmus or Avalon, I suggest following in the wake of the Catalina Express. They are fast catamaran ferries, and it may be hard to keep up with their 30 knot speeds, but that would be my suggestion. You can check their schedules on line. The Isthmus boats typically leave from Angels Gate and the Avalon ones from Queens Gate (LA and LB entrances respectively). You will want to leave early (like 8 or 9) and think twice about an afternoon ride back because it can be rough. At the Isthmus Cove, you can get a spot on the 'String Line' and in Avalon, there are small privately operated moorings on the east side of the pier in addition to some small municipal ones. Be sure to have warm clothes, a GPS and VHF radio and have fun!