Bava Batra

There was a certain river boat about which two men were disputing.  One said, 'It is mine', and the other said, 'It is mine. One of them went to the Beth din and appealed to them: 'Attach the boat  until I bring witnesses to prove that it belongs to me.' [In such a case] should we attach the boat or not?  R. Huna says we should attach it,  and Rab Judah says we should not.  [The Beth din having attached the boat],  the man went to look for his witnesses but did not find them, whereupon he requested the Beth din to release the boat, leaving it to the stronger to obtain possession.  In such a case should we release or not? Rab Judah says we should not release,  R. Papa says we should release.  The accepted ruling is that we should not attach in the first instance, but if we have attached we should not release. [If there are two claimants to a property  and] one says,' It belonged to my father,' while the other says, 'To my father' [without either of them bringing any evidence], R. Nahman says that whichever is stronger can take possession.  Why, [it may be asked,] should the ruling be different here from the case in which two deeds [of sale or gift relating to the same property and] bearing the same date