Sixth-rate was the designation used by the Royal Navy for small warships mounting between 18 and 28 nine-pounder guns on a single deck, sometimes with guns on the upper works and sometimes without. Sixth-rate ships typically had a crew of about 150 and measured between 450 and 550 tons. Usually sixth-rates were small frigates. Some larger ship-rigged, flush-decked vessels, were rated, which meant they were large enough to rate a Post-Captain in command, instead of a Lieutenant or Commander.
In later years sixth-rate frigates were sometimes called "jackass frigates", as they were really not quite big enough for proper frigate duties.
First rate Ship-of-the-line - 3 Deckers
Second rate ship of the line
Third rate ships of the line
Fourth rate ships
Fifth rate ships
Sixth rate Ships
Fire Ship of 14 guns