Third-rate

In the British Royal Navy, a third rate was a ship of the line which from the 1720s mounted between 64 and 80 guns, typically built with two gun decks (thus the related term two-decker). Years of experience proved that the third rate ships embodied the best compromise between sailing ability (speed, handling), firepower, and cost. So, while first rates and second rates were both larger and more powerful, the third-rate ships were in a real sense the optimal configuration.

Rating

When the rating system was first established in the 1620s, the third rate was defined as those ships having at least 200 but not more than 300 men; previous to this, the type had been classified as "middling ships". By the 1660s, the means of classification had shifted from the number of men to the number of carriage-mounted guns, and third rates at that time mounted between 48 and 60 guns. By the turn of the century, the criteria had grown and third rate carried more than 60 guns, with second rates having between 90 and 98 guns, while first rates had 100 guns or more, and fourth rates between 48 and 60 guns. By the latter half of the 18th century, they carried between 500 and 720 men.