[Ziro_of_the_Turks]

Pirates should have the best attacking ships.
Zormite should have the fastest ships.
Samurai ships should have the best "health".
Dustari ships should be balanced.
Forest shouldn't have ships. They're made out of wood, which comes from trees.

Edit: Or instead of making each kingdom have a different advantage, simply allow for ship upgrades. Also, maybe make the ground-cannon dockable onto the ship. This will make it so we'll have to take better care of our ships.