"There's a long tradition in ships of putting coins under the mast or in the keel as a good luck charm," said Kate Hunter, Newport Ship project leader.
The coin is inscribed in Latin and has a cross on one face. It was found in a hole cut above the ship's keel at the point where it connects to the stem-post, the timber which forms the bow.
The coin has been identified by expert Edward Besly from the National Museum of Wales as a petit blanc of the Dauphin Louis de France, who became Louis XI in 1461.
Minted in the town of Crémieu between 1440-56, the coin comes from Dauphiné, an area of south-eastern France traditionally held by the Dauphin, the eldest son of the king of France.