There are 3 levels of of trade ship, and 3 levels of warship. Like military units, higher levels require rarer materials.
The basic level just requires wood, and is a crude raft.
The next level requires copper, and gets you a small sailing ship for trade, and a small galley for a warship.
The third level requires bronze, and gets you a massive trade ship, or a powerful war galley.
The image at the top of the post shows a trade ship, a war galley, two smaller galleys, and a war raft. The structures along the coast with large dirt lots at the ports.