Perhaps. I know very little about ancient ships, but I believe the length of a perfectly normal (semi-local) merchant vessel would be between 20 and 30 meters, although smaller 10 to 20 meters ships certainly existed - I have seen one myself.
Further on, a trireme was about 35 meters long but it's a war ship and I'm unsure about how it would compare to grain ships. A trireme was, however, a fairly small war ship during the Hellenistic period from which the antikythera wreak originate.
Archaeologically I know of two ships over 60 meters from the greeco roman period: the ones at Nemi which meassured over 65 meters each (I believe one was close to 70). In the ancient literature we find that Isis (probably a fantasy ship) was a marvel to behold at ca 55 meters (Lucian - The Ship of Wishes 435-437).