“struggling as they rowed.” The apostles were struggling as they were being battered by the jerking of the oars while the ship itself was being battered (same Greek word) by the waves (Matt. 14:24).
“fourth watch of the night.” The Roman watches of the night were three hours each, and the fourth watch of the night started at our 3 a.m. and ending at our 6 a.m.
At the time of Christ, in both Jewish and Roman reckoning of time, the “day” was divided into 12 hours (John 11:9, “Are there not 12 hours in the day?). The first hour started at roughly 6 a.m. That made the “third hour” about our 9 a.m. (cp. Matt. 20:3; Acts 2:15); the “sixth hour” about our noon (cp. John 4:6; John 19:14; Acts 10:9); the “seventh hour” about our 1 p.m. (John 4:52), the ninth hour about our 3 p.m. (cp. Matt. 27:45, 46; Mark 15:34; Acts 3:1; 10:3); and the tenth hour about our 4 p.m. (John 1:39); and the eleventh hour about our 5 p.m. (Matt. 20:6).
Also, both the Jews and Romans divided the night into four “watches,” each being three hours long. This was true even though the Jews started their new day at sunset, at the start of the first watch of the night, and the Romans reckoned their new day at midnight, at the start of the third watch of the night (our day beginning at midnight comes from the Romans). That the Jews started their new day at sunset explains why the Bible usually puts the evening before the morning (cp. Gen. 1:5, 8; Dan. 8:14; 1 Kings 8:29; Mark 5:5; Acts 20:31).
The names of the four night watches were “evening,” “midnight,” “cockcrowing,” and “morning” (Mark 13:35: “So keep watch, for you do not know when the lord of the house is coming back, whether during the evening watch, or the midnight watch, or the cockcrowing watch, or the morning watch.”). Sometimes, however, the watches were just called “first watch,” “second watch,” “third watch,” and “fourth watch.” On occasion, the “watches” were not accurate enough, and so even the night was divided into hours. This is why Paul was taken to Caesarea at the “third hour of the night,” our 9 p.m. (Acts 23:23).
The hours of the day in Roman times were often approximations, because there was longer daylight in the summer and shorter in the winter. However, in both seasons the day was divided into 12 hours. Thus we would say that the “third hour” of the day was around our 9 a.m., not 9 a.m. exactly.
The feeding of the 5,000 took place in the area we know as Bethsaida-Julius, on the northeast shore of the Sea of Galilee (Luke 9:10). The disciples left that general area in the evening and headed for “Bethsaida” (Mark 6:45; cp. “Bethsaida in Galilee, John 12:21), which was apparently a small fishing village to the southwest of Capernaum (it can be confusing that the disciples left the area of Bethsaida and sailed toward Bethsaida. “Bethsaida” means “House of fishing,” and there were a couple of them on the Sea of Galilee). Thus the total distance the apostles had to row was likely somewhat less than five miles (eight km). This should have been an easy journey, but the wind was so against them that they had rowed for hours and were no doubt incredibly frustrated and near exhaustion.
“he intended to pass by near them.” Jesus would not have left the disciples in the lake in the storm, but wanted to pass close enough to be seen. The fact that they saw him on the lake was not an accident, Jesus intended for it to happen. It seems that Mark is intentionally borrowing from the Old Testament Hebrew idiom where God reveals Himself by “passing by” them. For example, God revealed Himself to Moses, saying, “I will make all my goodness pass by in front of you” (Exod. 33:19, cp. Exod. 33:22). Similarly, when Elijah ran from Jezebel, Yahweh revealed Himself to Elijah, and the text says, “Behold, Yahweh passed by” (1 King 19:11). Ezekiel 16:6 speaks of Yahweh passing by Israel when she was a forsaken baby and rescued her, then passed by again when she was of marriageable age and married her (Ezek. 16:8). In a similar way, Jesus, as God’s Messiah and representative on earth, intended to pass by the disciples in a manner in which they would see him and the situation would develop from there. Jesus’ walking on water was a teaching moment about trusting God for miracles and also Jesus continuing the process of the disciples recognizing him as the Messiah, which they fully acknowledged in Mark 8:29.