What about Blockader which blocks 7 hexes - the one it’s on and the six surrounding the ship?
If you do Blockader blocks settlement when it’s in port, then hopefully port movement costs resources.
For Leveling Up Buccaneers, I’m thinking a mixture of seniority (how many turns the buccanner was alive, maybe how many younger buccaneers are on its ship) and some kind of XP (how often the buccaneer gets to use it’s ability, maybe a max of 1 XP a turn so that bossers or certain combat buccanners get crazy amounts of xp by attacking a stack).
If every type of buccaneer gets a level up, then you can make a basic progression like “Lil’ Bosser” -> “Bosser” -> “Big Bosser” and standardize the bonus effect. Maybe it gives an extra bonus. Maybe it gives a related bonus. But it can’t be too complex, I don’t think, since we already have a wide range of basic abilities attached to the buccaneers.
(One thought would be to take some of the stronger buccaneers and move their stronger parts of their effects onto a separate stage. i.e. grappler’s ability to block upgrades could come at Level 2 “Grappler”. Or a chipper, slaver, etc might start by only effecting the “defending ship” of a stack, but once upgraded they can affect all ships.)
If you have Hero Buccaneers then they can have a short upgrade tree, which lets them pick up effects from different buccaneers as well as maybe unique bonuses?