Credits: TELUR Man
Pirate chests contain all kinds of goodies, ranging from Gold ingots to swords and useful materials. As I've said, you will stumble upon them occasionally in the world.
The Pirate ships will spawn too, but these ones are weird. You're supposed to be able to ride on them, but I was not been able to. Can't board them too, the character just gets through the boards. I was not been able to open the inventory or anything to put a saddle on, maybe. Hopefully, it was just my thing or a bug that will be fixed.