The Turkish Barbarossa brothers (especially Hayreddin) were a group of pirates/privateers who raided Catholic ships and cities in the Mediterranean. They were essentially given free reign in this regard by the Ottoman Sultan, along with some support, to counteract the Knights of Rhodes' privateering operations in the area. In doing so, their fleet consisted of Ottoman, captured, and newly constructed ships. For instance, after they captured the port of Algiers, Aruj Barbarossa declared himself Sultan and used the city's port facilities to help maintain and construct ships for his fleet. Then again, these pirate ships were mostly of the galley type, a smaller, short-range, and simpler design, which are not what most people envision pirate ships as. Also, Hayreddin ended up being elevated to Ottoman naval command for all intents and purposes, so he did have some official backing from the empire unlike some pirates.

Try this post, what you're asking was pretty much answered in it.