The sea was tossed by a great wind blowing.

 6:59-65 When they had heard this discourse many of his disciples said: "This word is hard! Who is able to listen to it?" Jesus well knew within himself that his disciples were murmuring about this; so he said to them: "Does this cause you to stumble? What then if you were to see the Son of Man ascending to where he formerly was? The life-giving power is the Spirit; the flesh is of no help. The words which I have spoken to you are spirit and life. But there are some who do not believe." For Jesus knew from the beginning who they were who did not believe, and who it was who was going to betray him. So that was why he often said: "No man can come to me, except it has been given to him by the Father to do so." 