Responsa for Bava Batra 151:7

במאי אוקימתא כרבי ספינה נמי תיקני במסירה דתניא ספינה נקנית במסירה דברי רבי וחכמים אומרים לא קנה

is analogous to that of the following Tannaim.<span class="x" onmousemove="('comment',' R. Nathan agrees with the Sages, and the first Tanna with Rabbi. ');">¹²</span> For it has been taught: Letters may be acquired by <i>mesirah</i>,<span class="x" onmousemove="('comment',' V. Glos. The buyer acquires the right to the debt as soon as the bond is delivered to him. ');">¹³</span> these are the words of Rabbi. But the Sages say: Whether [the seller] has written [a bill of sale] but has not delivered [the bond],<span class="x" onmousemove="('comment',' Even though the bill of sale had been delivered. ');">¹⁴</span> or whether he has delivered [the bond] but has not written [a bill of sale], [the buyer] does not acquire possession until [the seller] has written [the bill of sale] and delivered [the bond].<span class="x" onmousemove="('comment',' The delivery also of the bill of sale is assumed (Kid. 47b). ');">¹⁵</span> How has the matter been established? [That the first Tanna is] in agreement with Rabbi! Should not [then] a ship also be acquired by <i>mesirah</i>?<span class="x" onmousemove="('comment',' Why then does the first Tanna require meshikah? ');">¹⁶</span> For it was taught: A ship is acquired by <i>mesirah</i>, these are the words of Rabbi. And the Sages say: It is not acquired

Maharach Or Zarua Responsa