Our favorite game aboard SV Estrellita 5.10b is "Kill Doctor Lucky".
Imagine Clue, except rather than solving the murder, your goal is to get Dr. Lucky in a room, alone, with a murder weapon and kill him.
It is not an ideal game to store and play on a boat. There is a big box and a board and little pieces, making it bulky and difficult to play in a unsettled anchorage but it's worth it.
In college I was a fan of Cheap Ass games which I think was a Seattle based outfit. Originally they didn't have any color board games or pieces, you would order the game and it would come with just a booklet and cards and you would make player pieces out of whatever you had at hand. I think they were photocopying them in their garage and the games were...cheap. Now the games are slicker and marketed differently but the premises are still good.
In addition to Kill Dr Lucky, we have "The Totally Renamed Spy Game" which, prior to threat of lawsuit, was called "Before I Kill You Mr Bond". In this game you are an evil supervillian and your goal is to build a lair and kill spies but not have them blow up your lair. When a spy comes into your lair you have the option of killing him or her or taunting them at which point they are worth double points but might blow up your lair. The game is best if the players are willing to bust out some very good villian voices. It's funny and worth a twirl but doesn't have the staying power of Kill Dr Lucky.