It's grossly unrealistic when you consider some guys on a trireme having nothing but some arrows and maybe a few swordsmen can destroy tanks sitting on a transport.
What is the relevance of the cargo? tanks are just so much very heavy ballast on a transport. If the trireme has a ram that can hole the transport it may not be unrealistic. A transport loaded with tanks sinks real well.
..or a helicopter.
I can't fathom why helicopters can't fly over water.