The Ship Storage Barrel is a barrel that appears in the ocean if a ship sinks. It consists of every resources that was on the ship when it sank. It is a good way to get lots of loot after sinking an enemy ship or if you just happen to pass by it. The barrel can only stay afloat for a while until either someone takes all of the loot or it just despawn.
The location of the Ship Storage Barrel is at the approximate location in the ocean of a ship that sunk.
It consists of every resources that was on stored on the ship when it sunk. If you are low on resources, sinking a ship and taking stuff from the barrel is the best way to get loot.