Well presumably there would be no cargo, only prisoners as the cargo and the conditions would be...err...deadly pretty much.
It's odd though because when I think a large ship, I think a Spanish Galleon and according to a simple search, they only hold 150 people.
Not sure what they were carrying...
Acts 27:18,38 NKJV
[18] And because we were exceedingly tempest-tossed, the next day they lightened the ship.
[38] So when they had eaten enough, they lightened the ship and threw out the wheat into the sea.
Also, in verse 19, they threw the tackle out as well.
and here I thought those little Galleons held only about 80 people.