If boats are tied together, one may carry an object from one to the other on Shabbat.
On today’s daf the Gemara asks:
That is obvious, since these boats are like a single domain.
Rava said: This Mishna was necessary only to permit carrying from one boat to another via a small boat that is between them.
Rav Safra said to him: You, who are as great in this generation as Moses, did you speak well? We learned in the Mishna that one may carry only from one to the other, not via a small boat. Rather, Rav Safra said: The Mishna was only necessary to obligate one to place an eiruv, a joining of courtyards, between the two boats. Since the boats belong to different people, they must be joined to form a single domain in order to permit carrying from one to the other, as it was taught in a baraita: With regard to boats tied to one another, one places an eiruv and carries from one to the other. If the ties between them were severed, the people on the boats are prohibited to carry from one to the other. If they were then retied, whether unwittingly, i.e., the one who retied them forgot that it was Shabbat, whether intentionally, whether due to circumstances beyond one’s control, whether mistakenly, the boats are restored to their original permitted status.
The expression “Moses, did you speak well” appears several times in the Talmud. Rashi sometimes explains it as a reference to a prominent leader of the generation or a Torah scholar. Other times, he explains it as an exclamation by which one takes an oath in the name of Moses. Some explain that here the phrase is not an expression of wonder, but rather an expression of support meaning that Rav Safra agreed with Rava’s basic halakha. Yet he still commented that an analysis of the language of the Mishna indicates otherwise (Me’iri).