Translation:Shulchan Aruch/Orach Chaim/248
248: Law of One Who Sets Out on a Voyage by Ship and One Who Travels with a Caravan with Regard to Shabbat.
1 It is permitted to commence a voyage by ship, even on the eve of Shabbat, if he is traveling for the purpose of a Mitzvah. And he agrees with him to rest on Shabbat. And if he subsequently will not rest, it does not matter. But for a personal reason, one may not commence a voyage by ship within three days before Shabbat. Gloss: However, before three days, it is permitted, even in a ship that is dragged by animals – even if the depth of the water is less than ten hand breaths [Mahari"k, Shoresh 45]; 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.
3
Where it is permitted to commence a voyage on Erev Shabbat, if he entered the ship on Erev Shabbat and he established it as his place for Shabbos, even if it commences on Shabbat – it is permitted. And that is so only if he will not leave the ship from the time he established it as his place for Shabbat.
Gloss: And there are those who say that even if he left the ship, it is permitted, for after he established it as his place of rest from Erev Shabbat, it is permitted afterwards to enter it on Shabbat and to commence the voyage. And there are those who say that they make Kiddush on the ship and afterwards they return to their house and sleep there, and the next day, they return to the ship and begin to travel. This is the custom in a few places and one should not protest (R"an, first chapter of Shabbat; and Rivash, Nos. 17; 121; 122). And see below, Siman 339 and 404.
4 Those who go out on a caravan in the desert and all know that they are required to violate Shabbat since because of the danger, they will not be able to tarry in the desert on Shabbat by themselves – for three days prior to Shabbat, they are forbidden to embark. And on Sunday, and on Monday, and on Tuesday, it is permitted to embark. And if afterwards danger should happen to him and he will be required to violate Shabbat because of preservation of the soul, it is permitted and it is not considered a violation. And one who goes up to the Land of Israel, if a caravan became available for him, even on Erev Shabbat, since it is a matter of a mitzvah, he is allowed to leave, and he makes up with them to rest on Shabbat. And if after they'll be in the desert, they will not want to rest with him, he can go with them outside the Techum because of the preservation of the soul. And if he comes to one city on Shabbat, he walks throughout its entirety. And even if they left him outside of the city and he desires to enter the city, it is permitted, because since he left for a matter of a mitzvah, he has 2000 amot to every direction. Gloss: There are those who say that every place a person goes for commerce, or to see the face of his friend, it is all considered as a matter of a mitzvah. And it is not considered a personal matter except when he goes out for a stroll. And therefore it is the custom in a few places to be lenient regarding travelling by the ships and going out on a caravan within three days because they consider everything like a matter of a mitzvah, and we do not protest to this since they have upon whom they can rely.