The more interesting approach would have been to have privateers available as agents which could be given letters of marque by the major factions to make profits from commerce rading on that nations behalf. These privateers would then ocassionally go freelance, either becase they were not making enough profit, or because their employers decided their services were no longer required and in doing so they and their ships would become pirate pleets.

That would have created the proper relationship between the warfare of the period and the level of pirate activity in a region, whilst including another missing aspect of 18th Century warfare.