They could work like the Civ3C privateers and have a chance of producing another privateer when they kill an enemy ship. Do we know if they show their nationality or not?
Capture ships right? I thought I read they were doing that. It could have been speculation, but I think they should do it. Especially since privateers will be melee units.
I wonder if they will out range frigates. This should not be the case, because if privateers generally are smaller ships. A frigate would have a larger sail area and therefore should have more range. More sail equals more speed. Privateers should have high maneuverability though.
My point being that if frigates have a higher movement range, then they simply could stand off and sink privateers without much trouble, with ranged bombardment. So you would have to have many privateers to close in on the frigate and capture, board, or sink her.
What would be interesting is if a sailing ship loses range as it gets damaged. If it escapes it can refit somewhat at sea, but they could say a port would be needed for a complete refit.
One more thing I was thinking they should have is a merchant vessel which you can build and try to get to a friendly port and if you make it you get an 'x amount of gold. If catch privateers capture these on the high seas, then then have to bring the captured ship to a friendly port and get the gold. Or if a privateers captures a merchant ship it disappears and the gold is added to the treasury of the owning civ. This would give privateers their true purpose, to capture gold for the use of the mother country. To do it right the privateers of one country can only attack the mercant vessels of a civ they are at war with. After all they are not pirates right?
Of course in CiV privateers will be used to capture coastal cities, but I feel a dual purpose would make things more interesting. They can also pirate trade by standing off outside an enemy coastal city, just like any other ship.