There are currently three classes of ship that ply the islands within the Aether Sphere. The most powerful ships are naval armour-clad ships that utilise a number of innovations to create platforms of destruction. The first is that the use a full (and very expensive) disc of aetherite to provide a spherical plane of propulsion. This allows the ships to perform amazing aerobatics for ships of their size. The second is the inclusion of metallic armour on their hulls, providing them with substantial projection from aether cannon or clockwork bombardment. These ships are the projection of power for the various island nations and they each have their specialities - the Lombardis are the most advanced, the Teutons the strongest and the Frisians the fastest.
The majority of ships that sail the aether are modelled on traditional sailing ships, with masts and sails to catch the wind (with many of the ships taking advantage of the increased dimensions of the ships to run up even more sails). In these ships - usually merchant vessels - lift is given through aetherite whereas forward motion is given through a combination of aether and wind power. They are nowhere near as fast as the military vessels, nor as agile, but they are much cheaper and easier to maintain ... and they can, of course, land in water!
The last class of ships cannot really be called that - they are more enhanced balloons. The slow, ponderous and silent flight of the air-hulks is a common sight around the island nations. The balloons are filled with charged aether gas - providing an unnatural amount of uplift, giving these massive hauling ships their strength to carry their cargo. They are, however, ponderously slow and of no use militarily.