In the late 18th century, shipbuilding in Spain followed the rules set out in the "Guidelines for the Wood Required to Manufacture the King's Vessels," written by José Joaquín Romero y Fernández de Landa (the first Naval Engineer of the Spanish Royal Navy). It was written in 1782 and approved 2 years later by the Spanish king, Charles III. The book established the designs for the ships of the line that took part in the great naval battles of the late 18th and early 19th centuries.
According to these guidelines, the frigate "Mercedes" should have carried 34 guns: 26 12-pounders on its gun deck and 8 6-pounders between the quarterdeck and the forecastle. However, according to contemporary descriptions, it had 38 guns.
This is a life-sized recreation of a section of the half deck on the frigate "Mercedes." One of its 26 12-pound cannons can be seen.