The sea was tossed by a great wind blowing.

 6:66-71 After this many of his disciples turned back and would not walk with him any more. Jesus said to the Twelve: "Surely you too do not want to go away?" Simon Peter answered him: "Lord, to whom are we to go? You have the words of eternal life; and we have believed and we have come to know that you are the Holy One of God." Jesus answered them: "Did I not choose you twelve, and one of you is a devil?" He meant Judas, the son of Simon Iscariot, for he was going to betray him--and he was one of the Twelve. 