Abandoned ships occur at various locations around the North Atlantic and River Valley map. They appear as a ship icon with flames on the map. When you arrive at one of these locations, you’ll see a ship on fire.
If you jump off the Morrigan and swim over to the ship a countdown timer will appear on screen. At this point, you can run around on the deck of the ship and loot a number of treasure chests that appear here for small amounts of cash and resources. Just be sure to get off the ship before the timer runs out as it will explode!