Jackdaw is Edward's personal ship. It was named after a common Welsh bird. Through the game you find resources that you can use to upgrade your ship. Jackdaw can be used to explore the Caribbean. Jackdaw is concidered as the second main character in the game.
Diving bell is one of the major upgrades for Jackdaw. Diving bell can be used to explore shipwrecks that can be found around Caribbean. You can find treasure chests which can contain upgrade plans for Jackdaw or money, for example.