See this miracle of walking on the sea explained in the notes at Matthew 14:22-33. Compare Mark 6:45-52.
Immediately - Quickly. Before a long time. How far they were from the land we know not, but there is no evidence that there was a miracle in the case. The word translated “immediately” does not of necessity imply that there was no interval of time, but that there was not a long interval. Thus, in Matthew 13:5, in the parable of the sower, “and immediately (the same word in Greek) they sprung up,” etc., Mark 4:17; Matthew 24:29; 3 John 1:14.