Boat's speed in Jesus days

Question

In Mark's gospel we read about Jesus and his disciples moving in a boat from Capernaum to Dekapolis, to a place in the other side of the Sea of Galilee about 20 kilometers away south. They set out in the evening/afternoon (chapter 4 verse 35), and arrived in the next day, since he cast cast out dimens, and the local herders were witness of it (chapter 5 verse 11, 14). The demonized men met him immadiately as he arrived (chapter 5 verse 2), which means that he didn't sleep on the shore till the day dawn, but arrived in the day time.

So, it seems that it took them a whole night to cross the lake (having in mind that they went through a storm which "Stole" from them some precious time - chapter 4 verse 37). We can see, however, that in the next day they returned to Capernaum, and surely arrived not late in the day, seeing that it was a day full of events.

So, the question is, what is the estimated average speed of fisherman boat of that time? How much time would it take with a calm water to pass these 20 kilometers from one tip of the Sea of Galilee to the other tip?

Answer 1

An ancient sailing vessel had a hull speed of about 6 kilometers an hour but with a storm that speed could increase dangerously to perhaps 12 kph. With winds in the wrong direction, that could be going backwards.

Boat speed was highly dependent upon the wind strength and direction. In fact, the square rigged sailing vessels of the time would find it difficult to make any headway to windward.

The Mediterranean square-sail allowed vessels to sail at a steady speed day and night. In good weather, with a favourable wind from the side or behind, a vessel could reach average speeds of between four and six knots. If the wind was blowing in the wrong direction progress was very slow and only the most well-maintained vessels with the best crews were able to sail against the wind at an angle of no more than sixty or seventy degrees. Literary sources suggest that most sailors preferred to wait in port for better weather.https://www.futurelearn.com/courses/shipwrecks/0/steps/7964

Effectively, sailing against the wind requires tacking - going back and forth sideways to the wind direction in a zigzag fashion - doubling or tripling the transit times.

In addition, boats could be rowed, but this would have been very inefficient going against the wind. https://onlinelibrary.wiley.com/doi/full/10.1111/1095-9270.12278

It would not be unusual for one leg of any round trip to be against the wind and one leg running with the wind. In this case, one way would be much shorter than the other.

The prevailing winds in the Sea of Galilee are NorthWest or SouthSouthEast. Thus traveling from Capernaum to Dekapolis, the winds would be either blowing from directly behind, or blowing from directly ahead.

On a calm day, with a favorable wind, you could expect the trip to take perhaps 6 hours. On a day with unfavorable winds you would never leave the harbor.