Nef de Joie
A magical vessel constructed by Merlin for the king of Northumberland and his friend Agad.
The ship came into possession of Mabon the Sorcerer, and he sent it to Tristan, so that Tristan could join him in a struggle against Mennonas, an enemy.
The ship appears in French romances, where Merlin stipulated that it was to be destroyed following Arthur’s final battle, but whether or not it actually was remains a mystery.
Source
Prose Tristan | 1230-1240