Reference for Bava Kamma 232:8
ורשאין הספנים להתנות שכל מי שאבדה לו ספינה יעמיד לו ספינה אחרת אבדה לו בכוסיא אין מעמידין שלא בכוסיא מעמידין לו ואי פירש למקום שאין הספינות הולכין אין מעמידין
[his request should be complied with]: we are therefore told that there is a difference between guarding one and guarding two.<span class="x" onmousemove="('comment',' As when he has two asses of his own among those of the other drivers he will put more heart into his work. ');"><sup>15</sup></span> Our Rabbis taught: If a boat was sailing on the sea and a gale arose threatening to sink it so that it became necessary to lighten the cargo, the apportionment [of the loss of each passenger] will have to be made according to the weight of the cargo<span class="x" onmousemove="('comment',' Though one might be asked to throw away gold and another a similar weight of copper. ');"><sup>16</sup></span>