Standard roman transport ship without battle abilities.
Consul, grabbing ships from merchants is the fastest way to gather an invasion fleet. But it is costly too! The merchants will not be happy, so we must give them enough money to stop them from bad-mouthing you to the citizenry. Do not expect also that these ships could hold their own in a battle - if they meet a proper fleet you will lose both the ships and the men aboard.
The Oneraria, also called 'Navis Oneraria' or 'freight ship', was a ship type whose shape is best described as short, round and similar to an egg, and usually it had one mast with a large square sail. It has no oars but a large cargo hold. The length-width-ratio was around 4:1 which gave it better lateral stability than a common rowing warship of this era (8:1 to 10:1 relation). As the name says, Onerarias were the typical freight ships in the Mediterranean. A widely used ship class of the Oneraria type is the roman "Corbita", with a cargo capacity from 60-300 tons, some variants may carry even 400 tons and more. The ships may be different in size but looked about the same: one large square sail with a couple of triangular sails (called a 'siparum') and one small mast at the bow with a smaller sail (called a 'artemon'). They also had two side-rudders which were connected.
Historically, Roman Corbitas were used on nearly all trade routes through the mediterranean world. They carried grain from Africa, garum from Iberia, metal, silks, olive oil, wine, luxuries or wild animals from all Roman provinces. While some small variants were able to sail the Tiber river to Portus, the port of Roma, the larger ones had to be unloaded at Ostia. It is said that the small corbitas carried up to three thousand amphorae (or 150 metric tons), the biggest ones may have borne up to ten thousand amphorae (about 500 metric tons). One piece of archeological evidence is the "Mahdia ship", which was found on the coast of Tunisia and is dated to 100 BC. Other examples date from 200 BC to 300 AD.