Privateers were a kind of prettied-up pirates. Ships and captains - not belonging to the government's navy, but private vessels - were given papers (letters of Marque) making it legal for them to attack foreign shipping. The privateer would then share the take, or profit, from the capture with the government. So these were the kinds of (presumably French) ships Wentworth was talking about "taking" and would have added considerably to his own fortune as well as being "entertaining." ;-)