Magical or mystical ships figure very largely in the Adventures of the Grail. The pattern is that an unmanned ship comes ashore, you find it and get in, and it takes you somewhere, usually to a physical and/or mystical adventure. It can be quite dangerous.
Chief of the holy ships is Solomon’s ship. The vessels need not, however, be holy or mystical. In Malory IV, Morgan le Fay apparently sends a similarly mysterious ship to entrap Arthur. In Malory X, Tristram (Tristan) and Palomides find “a rich vessel hilled over with red silk” in which lies the body of the murdered King Hermance, with a letter in his hand telling his story and asking for an avenger. Here there seems to be no magic, simply human device. Remember also the barge in which, at her own dying request, the body of Elaine of Astolat is placed to go to Camelot; her barge, however, is steered and rowed by a bargeman.
At the dying request of Percivale’s saintly sister Amide, Galahad and his companions put her body into a barge covered with black silk and set it adrift on the sea, to meet them again in Sarras at the end of the Grail Adventures. Lancelot, finding and entering this ship,
felt the most sweetness that ever he felt, and he was fulfilled with all the thing [sic] that he thought on or desired.
The Lord fed him as the Israelites were fed with manna, and he stayed with the ship for many months, during which time he was joined for half a year by his son Galahad. Occasionally they left the vessel for a time to adventure on land. About a month after Galahad quit the ship for good, it brought Lancelot to Carbonek, leaving him there to his own Grail visions while it proceeded on to Sarras with Amide’s body, which had apparently remained fresh and sweet in the best tradition of saint’s bodies.