Eruvin 42 – Shabbat on a ship

If gentiles took him away from his residence area (techum) on Shabbat and brought him into a fold or corral, can he walk the complete area of the corral? Rabban Gamliel and Rabbi Elazar say that, since it is a private area, he can freely walk there. However, Rabbi Yehoshua and Rabbi Akiva contend that because he lost his techum, he can walk only four steps around, and that's it.

It once happened that these same four people were on a ship. When Shabbat started, they were in a port, but later the ship moved out to sea, and they lost their original techum. Following their respective opinions, the first pair moved freely around the ship, but the second one only walked for four steps around.

However, upon closer examination, even they could walk the complete ship – is' just that they chose to follow this additional stringency, in order not to mislead the people who would not know the difference between placed in a corral and on a ship. And what is indeed the difference? With the corral, one did not acquire residency there before Shabbat, but instead was brought there. However, with the ship, one acquires his residency there at the beginning of Shabbat. Others say that since the ship keeps moving, he is always walking only four steps – except these four steps keep changing as the ship moves. Why do we have to come up to this reason, which seems artificial? – Because the walls of the ship are not made to enclose him, but rather to keep the water out.

What is the practical difference between the two explanations? – If the walls of the ship break, or if he jumps to another ship – he would be allowed to walk there only according to one explanation but not the other.

Art: Winslow Homer - Observations on Shipboard