Brendan and company embarked from the Isle of Birds on Pentecost. After 40 days at sea, they began to be chased by a great sea beast. Brendan’s monks were greatly afraid of the beast but Brendan calmed them and told them to have faith in God’s protection. As the beast grew so close it began to swamp the boat, Brendan raised his hands to the heavens and said, “Lord, deliver your servants, as you delivered David from Goliath, the giant, Lord deliver us, as you delivered Jonas from the belly of the whale.’
After Brendan repeated his plea three times, another great beast appeared coming from the opposite direction and began to chase the first beast that was harassing them. The beast sent by the Lord cut the first beast into three pieces before their eyes and then returned to where it had came. They sailed on.
The next day, they saw a forested island at a distance. As they approached the island, they saw a large portion of the beast laying on the shore. Brendan told them, “See what wished to devour you! You now shall devour it!” They beached their boat in a safe place and Brendan chose a place for them to camp.
Brendan instructs the monks to gather enough meat to last for three months because all of the remaining meat will be eaten by beasts overnight. The monks then ask Brendan how they can remain there for three months without water or other food. Brendan told them that God would provide and to search the other side of the island where they found water and roots. They remained on the island for three month because the seas were too stormy to sail upon.
Later the monks found that the remains of the beast had been indeed entirely devoured, leaving only bones. They tell Brendan and he tells them he knows they would would test him. He then tells them that they would find more meat there tonight and that they should carefully salt it because it was getting near time to leave this island. Brendan had them load the boat with the meat, roots and water. Brendan himself had not touched meat since his ordination, that was taken only for the monks.They then set sail again heading north.
WRJ Barron and Glyn S Burgess. (2005) The Voyage of St Brendan: Representative Versions of the Legend in English Translation. University of Exter, Press.