Question (Ri): In Shabbos (100b), we say that wastewater of a boat, we cast it on the sides of the boat, because (he does not directly throw to the sea. It is only through his Ko'ach (impetus)), and they did not decree about his Ko'ach in Karmelis, even though it falls immediately to Karmelis. For this reason, it should be permitted also here!

Even the latter version permits spilling only because he is not concerned lest [the wastewater] go out to Karmelis, like Rashi explained!

Answer: In a balcony, sometimes when they spill water from it, it goes immediately until the place where Reshus ha'Rabim goes in a puddle, and this is his Ko'ach in Reshus ha'Rabim. Chachamim did not distinguish in all balconies;

However, in a boat it is totally uncommon that it goes near a puddle.

Explanation #1 (Rashi): He knows that within four Amos there is enough for two Sa'im of water to be swallowed, that a person uses each day.

Support: This is why it says in the Gemara that [the water] finishes in a Chatzer of four Amos.

Consequence: According to his Perush, that we discuss a Biv (drainage channel) that has four by four Amos, for if it is less than this, the water does not finish, like regarding a Chatzer, like Rashi explained in the Gemara. [If we would not say so,] which Shi'ur was given for the width?

Explanation #2: The reason for covering a Biv is due to suspicion. Since it is covered for four Amos in Reshus ha'Rabim, one who sees water leaving the Biv does not think that it comes from the Chatzer, since it is distanced four Amos from the Chatzer.

Support (for Explanation #1): The Gemara compares four Amos of a Biv to four Amos of a Chatzer. It says that the entire [Mishnah] is R. Eliezer ben Yakov.

Observation: According to the Rashbam, a channel covered for four Amos in Reshus ha'Rabim, one may spill water in it on Shabbos, for we hold that the teachings of R. Eliezer ben Yakov are few but clean (the Halachah always follows him);

Opinion #1: However, according to Rashi, the reason is because [the water] is absorbed. It is forbidden, for in wood it is not absorbed.

Opinion #2: However, the Ri says that even if it is made like a stone floor, it is swallowed (Tosfos ha'Rosh - between the stones), and it is permitted.

Explanation #1 (Rashi): [The Beraisa asks] in what case [does our Mishnah] obligate an Ukah?

Consequence: According to this, we must say according to Rav Nachman below, it means "in what case do we obligate an Ukah of Sa'atayim? [It is in winter,] but in summer, he does not need an Ukah of Sa'atayim, but he needs an Ukah of a Se'ah";

He may spill only as much as the measure [of the Ukah]. Rashi explained like this below.

Implied question: Why didn't the Gemara bring this Beraisa above [in the discussion] on our Mishnah of an Ukah? (Perhaps the Seifa of our Mishnah, which discusses a Biv, was a separate Mishnah in Tosfos' text. Alternatively, Tosfos means "the Reisha of our Mishnah, which discusses an Ukah.)

Answer: It is because it wants to challenge it from our Mishnah of a Biv.

Explanation #2 (R. Tam): This Beraisa refers to our Mishnah "one may not spill on a Biv."

Implied question: Why did [Abaye] say "but behold, wastewater...?" (Also the Beraisa discusses this! This connotes like Rashi, that the Beraisa refers to the Reisha, in which he pours water to prevent dust from rising. Only the Seifa, regarding a Biv, discusses wastewater.)

Answer: He means "but behold, a Biv..." (I.e. our Mishnah discusses a Biv in summer, and it forbids spilling - Gevi'a ha'Kesef.)

Correction: The text says "rather, for what should we be concerned?", and not like is written in Seforim "rather, there..." (The text "there" connotes that Abaye's question is not from the matter that the Beraisa discusses.)

Explanation: This is not precise. Rather, one may put into it even two Kor (or more). If not, there is no difference between [if it holds] Sa'atayim or one Se'ah (in either case, one may put as much as it holds)!