Frigates of the time were typically classified as either 5th or 6th rate vessels, carrying around 40 guns across 2 decks, making them manoeuvrable enough to act as scouts, raid shipping, but still take part in larger fleet engagements when they needed to.
Brigs were two-masted sailing ships with square rigging, and were popular as both merchant ships and as light escort craft. Only carrying 10-20 guns on a single deck meant they were not particularly suited to heavy combat, though they made excellent training vessels for cadets.
