Just added these to the main post:
-Maelstrom battle from At World’s End. Ex: big whirlpools that ships can get stuck in as they go around it in a circle on bad rolls. +Big whirlpool “black hole” that sucks all game pieces toward it on a roll of 1 each round? Or, have a circular ocean that is one big whirlpool. There are different “lanes” in which concentric circles determine where the ships are each round. At the end of each round of turns they move one section closer to the center of the whirlpool, effectively meaning the game has a timer. Might be best in a 1v1 deathmatch. The goal is to sink the other ship before yours gets sucked in, or simply outrun the whirlpool somehow (maybe tossing cargo gets you one lane towards the outside of the whirlpool). Lots of different ways to do it, and you could make alternate versions that would work in a regular game with gold, or a 1v1 deathmatch that simulates the movie scene as much as possible.
-Expanding upon the Race scenario linked above: line (“drag race”) vs. circle/oval (or other!), have islands with UT’s on them (power-ups/upgrades/etc), shortcut opportunities, NPC creatures.