The San Carlo Borromeo-class ships of the line were a class of two 66-gun third rates built by the Venetian Arsenal from 1750 to 1793.

Being built to hold 66 guns, by Venetian standards were considered Vascelli di Primo Rango, or first rate ship of the line.

By contemporary Royal Navy standards, though, this number would make them third rate ships of the line.

[2] The namesake ship, the San Carlo Borromeo, was haunted by a recurring problem: in stormy seas, it had a tendency to lose the rudder.

The only other ship made with the same plans was subsequently modified in 1788 while still in the dockyard, resulting in a great improvement in maneuverability and sailing speed.