Warships carrying cargo in the age of sail

Did age-of-sail navies use warships as cargo ships during peace to earn money?

Yes, especially in Venice and in arrangements that allowed captains to carry trade, although the revenue often benefited the captain rather than the state directly.

Sailing navies did not always keep state ships in a purely military role when no war demanded them. The exchange also cautions that private opportunity for officers and national revenue were not the same thing.