Adam Clarke on John 6:19

Had rowed - Their vessel was a small one only, something of the boat kind: as to sails, if they had any, they could not now venture to carry them, because of the storm.

Five and twenty or thirty furlongs - Between three and four miles. The sea of Tiberias, on which they now were, was, according to Josephus, War, book iii. chap. 25, forty furlongs, or five miles in breadth; and one hundred and forty furlongs, or eighteen miles, in length. Pliny, lib. v. chap. 15, makes it about six miles broad, and sixteen long.

They see Jesus - See the notes on Mat 14:25, etc.