There are several aspects of Fortune which seem to be connected with merchants or sea-voyages; though the links are admittedly tenuous, I've grouped them here for convenience.
Fortuna Felix is another aspect of the much-beloved Roman Goddess of luck, Fortuna. Her title means "Happy" or "Blessed", "Lucky", "Favorable" or "Fruitful". She seems to have been one of the dual Fortunes worshipped in the city of Antium, where They had a famous oracle. She was depicted on coins of the Empire with a cornucopia, symbol of the great good things She could provide, and a rudder to show that She was the one Who steered the fate of humans. She could also be shown standing of the prow of a ship, or sometimes with the caduceus, usually a symbol of Mercury or Hermes. As Mercury was a God of travellers and merchants, perhaps this aspect of Fortuna was especially helpful in bringing luck to business ventures or overseas trade.
Fortuna Tranquilla was invoked to bring prosperity in sea-voyages, as She could bring calm weather on the seas. And as tranquilla could also refer to other sorts of quiet or calm affairs, perhaps She was the Fortuna Who brought the stability of circumstance and calmness of mind that could form the basis for level-headed and successful dealings in business ventures.
There is also a Fortuna Gubernans, meaning "Fortune Who Steers or Guides" (from this root comes our words "governor" and "gubernatorial"); She too was shown with a rudder and horn of plenty. Though many varieties of Fortuna were shown with ship parts, Fortuna Gubernans may have been more specifically concerned with sailors and ship voyages, and "fortuna" is a term still used by Italian sailors for a storm at sea.
Then there is Fortuna Navirilis; I'm not sure what the meaning of this epithet is, but it may be related to navis, "ship"; if so She would presumably be another form of Luck concerned with sea-voyages.
Fortuna Felix may be associated with the Goddess Felicitas, the personification of happiness.