“If this ship isn’t assigned a Helmsman crew, roll a d6 after this ship resolves a move action. On a result of 4-6, this ship can move L.”
According to page 29 of The Pirate Code, this ability happens after a shoot action provided by a captain. How does the timing work with explorers and S-boarding?
This ability applies after the ship resolves the move action, so you do all of the usual effects that would be attached to a shoot action (captain, explorer, s-board, ram, board, etc.) first, then after all of that is completely finished, only then do you get to roll for the extra L.
You can use it to dock the ship, but because it’s not part of a move action, you can’t use any other move action abilities or effects with it, whether you’d used them with the original move action that triggered it or not.