Embarking on Ships
2. A Jew is permitted to journey on a riverboat under all circumstances,
even on Friday (1), provided he will not be required to perform forbidden
labors on Shabbos. Permission is granted even if the boat is drawn by
animals [ which are walking along the river banks](2).
(1) As we saw yesterday, travelling on a river, according to the Sages,
does not mess up one's system in the way that a sea-journey would;
consequently, embarking on a riverboat on Friday would not detract from
one's Shabbos enjoyment and is permitted.
(2) It is Rabbinically forbidden to ride an animal or even in an
animal-drawn carriage on Shabbos, because the Sages feared that one might
inadvertently snap off a tree branch with which to hit the animal. This
prohibition doesn't apply to boats which are pulled down the river by
animals walking on the riverbank, because the animals are a great distance
from the boat itself.