While there is no ocean going ship in Parzival, nor is there a boat that brings Gawan to the grail, he must pass over a river to reach a marvelous castle:

A causeway with very heavy going led to a broad fast-flowing, navigable river, and he and his lady rode towards it, Beside the quay there was a meadow where much jousting was done. The fortress loomed above the river. (271)
Before crossing he jousts an unfriendly knight and having defeated the knight, offers the knight's horse to the Ferryman who must take him across. The friendly Ferryman takes Gawan across in his boat and provides for the night. The next day, Gawan sets off for the marvelous castle.