Les, have you got a copy of "The Frigates: An Account of the Lighter Warships of the Napoleonic Wars, 1793--1815," Author, James Henderson, CBE, copyright 1994? Interesting discussion of actions and vessels. He defines rated vessels as those requiring a Captain. According to his table at the back, a sixth rated was 20 to 24 main deck guns and the smallest frigate was 28 guns. If he's right then we've all been wrong in our definition of the marginal vessels.