and even in a case where the Jew will then be required to do a Melacha on Shabbat in order to steer the boat. [Rivash, No. 152]. And if it is a short journey, e.g. from Tyre to Sidon which is just one day's journey, it is permissible to commence travel on the eve of Shabbat, in the morning, since it is possible that he will arrive there before the Shabbat. And in a place where it is customary not to commence a journey on the eve of Shabbat at all, even a short journey, it is forbidden to do so.
2
The reason it is forbidden to commence a voyage by ship within three days before the Shabbat is because of the enjoyment of Shabbat, since for the first three days they experience pain and confusion. And this only applies to voyages in seas of salty waters; but travelers in rivers do not experience pain and it is therefore permitted to commence a journey in them even on the eve of Shabbat. And that is only provided that it should not be known to us that the depth of the waters is less ten hand breaths; but in a place where it is known to us that from the bottom of the boat to the bottom of the river, the distance is less than ten hand breaths, it is forbidden (to travel outside of the Techum) because of the prohibition of Techum.
Gloss: And Likewise, in a ship where the Jew will need to perform Melacha on Shabbat, it is forbidden to enter it three days before the Shabbat, even if they are flowing rivers and he is above ten (Rivash, No. 152; Mahari"k). However, there is no prohibition with that that the animals drag the boat on the bank of the river and it is not likened to traveling in a wagon, which is forbidden.
