1) THE BOAT THAT SANK WITH THE WINE
QUESTION: The Gemara discusses a case in which a person rented a boat from a boat owner (without specifying any particular boat -- "Sefinah Stam") to transport specific barrels of wine ("Yayin Zeh"), and the boat sank at sea with the wine. The renter is obligated to pay rent for the boat, because the boat owner may claim that he is willing to provide another boat to transport the wine. The renter must pay rent because it is his misfortune that he no longer has those specific barrels of wine to transport (since they sank).
Why does the renter have to transport those specific barrels of wine? Why can he not accept a different boat from the boat owner and transport different barrels of wine? The Gemara earlier (77a) quotes Rava who says that if an employer hired workers for one day to do a specific job and the workers finished the job by midday, the employer is entitled to give them other work to do (of an equivalent degree of effort as the first job). It is clear that an employer is entitled to substitute the specific work for which he initially hired workers to do for other work (as long as the new work is not more burdensome). The same should apply to a renter: he should be entitled to substitute the specific work for which he initially rented the boat for another form of work. Why, in the case of the Gemara here, may the renter not bring other barrels of wine to be transported, and demand that the boat owner provide him with another boat? (See HAGAHOS ASHIRI to ROSH 6:5.)
ANSWER: The KETZOS HA'CHOSHEN (311:1; see also SHACH 311:1) writes that there are a number of answers to this question, but that the most likely answer is that only in the case of the Gemara here can the owner of the boat limit the rental to the transport of the specific barrels of wine. Since he lost the boat in the process of transporting the wine, the renter is not entitled to demand another boat with which to transport other wine. Rather, the renter must pay the rental fee for the original boat. In contrast, in the case of the workers who finished the job early, the workers have not lost anything in the process of doing the original work, and therefore the employer is entitled to give them other work. (Y. MARCUS)
2) PAYING FULL RENT FOR A BOAT THAT SANK
QUESTION: The Gemara states in the name of Rebbi Nasan that in a case in which a person rented a specific boat ("Sefinah Zu") for the purpose of transporting specific barrels of wine ("Yayin Zeh"), and the boat sank after traveling only half of the distance for which it was rented, the law is that "if he has already paid, then the money is not refunded, but if he has not yet paid, then he is exempt."
Why, if he has already paid, does the renter not receive a refund for at least half of the cost of the boat? The boat transported his wine only half of the way! (TOSFOS DH Iy)
ANSWER: TOSFOS answers (as explained by the KEHILOS YAKOV 46:4) that there are two types of rentals. When one pays the entire sum of rent at the commencement of the rental term, the object (such as the boat) becomes completely his (he has temporary ownership) for the purpose for which he rented the object (in the manner of "Dekel l'Perosav"). Hence, even if he did not succeed in using the object in the manner in which he intended (such as when the boat sank), he nevertheless is obligated to pay the entire rental fee because he acquired the object. If, however, the renter did not pay at the commencement of the rental term, the rental is viewed merely as a right to use the object of the other person (and not that the renter actually has ownership of it), and thus the renter pays only for as much use as he was able to obtain from the object.
Therefore, in Rebbi Nasan's case, if the renter has already paid the entire rental fee for the boat, then he has acquired the boat and is not entitled to a refund. If he has not yet paid the rental fee, then he has not acquired the boat and he is obligated to pay only for the amount of use that he obtained from the object. Since in this case the use of the boat was virtually worthless (the boat sank and did not accomplish anything), the renter is exempt. (Y. MARCUS)