And now to the culprit that left me wanting something better, the sea. I thought about it for a while and I decided a cool archetypal challenge for the sea would be your crew. What, you think you can drift around in the doldrums for weeks without hearing some grumbling from those shady characters you hired at the last port? Here's what I came up with:
Each following day move one square, encounters don't matter any more.
When you land on a square with a black spot your crew has become unhappy and is grumbling. Roll 1d6 to see how they challenge you.
If one of the party members has an exceptional score in the ability challenged the crew is appeased and you halt their descent into darker moods. An exceptional ability can only be used once a journey.
If you don't have the right ability bonus you can offer up the secondary item: a change of scenery, wine women and song, or cold hard cash. As long as you meet their challenge you can hold the crew's discontent on that square. But every day you'll have to roll for another challenge.
Fail the challenge and the marker moves to the next box. Once you get to the fork, a challenge failed for 3 starts the crew spiralling into madness, depression, and possible suicide. A failed 4 or 5 will head them toward angry revolt, and either assaulting or marooning the party.
Keep in mind, successfully meeting the challenges will only stall the inevitable. Once the game is started the only thing that can reset the board is port, or at least having the majority of the crew go ashore somewhere.