If all the pirates aboard a ship at sea leave, the ship is considered abandoned. The ship will not continue along its route while it is abandoned. Ships that are abandoned at a league point will remain there; however ships that are between league points may still be engaged.
A ship that is abandoned will reset after a short period of time (usually 10-15 minutes), and will port automatically at the most recently visited island. This is commonly known as autoporting. A ship that has reached the final league point before its destination will reset to the destination.
All booty on board an abandoned ship will be lost when the ship is reset, but everything in the hold is retained.  During a blockade, ships with little or no stock aboard them are sometimes abandoned between rounds. This saves time by not having to navigate the ship off the board. At the start of a new round, the board resets, ejecting abandoned ships from the board to the island's league point. These ships can be manually ported after the blockade ends, subject to there being no embargo in force on the nearest island.
Abandoning ship for over fifteen minutes with gems in the hold will cause the gems to be stolen by mysterious forces, never to be seen again.