Wrote a paper on Zheng He's voyages some time ago. Zheng He was an eunuch admiral of early Ming dynasty China, who made several tribute-collecting trips all the way to the Indian Ocean and even Africa with a huge armada of Chinese 'treasure ships', possibly the largest wooden sailing ships ever built. Basically the Emperor sending off people to tell the world how awesome China was and to send them tribute, not really voyages of discovery in the sense we know.
The ships used in Chinese shipcraft at the time were flat-bottomed junks, which is good when you're trying to sail in shallow waters -- like the coast and rivers of China -- but less good in rougher seas. Even though a flatter-bottomed ship is stable, more stable than a western ship with a "high" front-profile and ballast, if it capsize, it stays capsized, and if I understand it correctly, junks aren't even that good at avoiding flipping over. It's a bit like they have their feet on both sides of the fence: they have a single hull, but it's flat, and thus they're not necessarily horribly good at anything in particular, just muddling along.
If you take the concept of a raft, though, a flat-bottomed, low-profile ship, you come across the catamaran design. Catamaran are the other branch of shipcraft in human history, descended from wooden canoes just as single-hull ships of the west are. The single-hull ship is a canoe with rocks on the bottom as ballast, and the catamaran is two canoes put together sans ballast.
A catamaran is very stable, and lies lightly on the water. It also can take bigger loads of cargo than single-hulls (relative to idno weight or size) because they don't have ballast, and they don't sink like single-hull ships: they'll bob on the water instead. Some disadvantages include that fact that if a catamaran DOES turn over, you won't be turning it back easily (though it'll stay on the surface), and that it doesn't handle riding certain kinds of waves as well as a single-hull ship (which can cut through them).
So here's a design for a large catamaran, a what-if on what they might look like if they had been developed as far as Old World sailing ships were. This is for Ysi. Got the inspiration to do this from my current map project: this'll be a great little pic on the sea, after abstracting it a bit. The sails are junk-style.
Done in Google Sketchup.
The old paper style is just a quick application of my paperising script (findable here) and some other stuff.