In the rating system of the 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.