I must disagree with Dobbsy. Some fleets are more or less balanced, but all the extensions are important.
Dwarf fleet is just good to go in the trashbin if you don't add the Dreadnought ship, presented in the first extension (sea of blood).
Chaos dwarves are powerfull but they can be beaten with some good tactics, and to have powerfull fleets is always a good idea when you want to have hard time playing, or if you're an experienced admiral playing against a rookie.
Anyway, this game is just great ! I fell on Warmaster because i could not find any player here (nearly), but i really like this game, one of the very best GW ones in my opinion.
The rules smell like old school, but you really have a lot of fun during the games. The game is far better than Dreadfleet if you know this game, and the only good game to play big sea battles.
You must visit TheSeaOfClaw yahoo group, and the blog :
http://groups.yahoo.com/group/theseaofclawshttp://theseaofclaws.blog.fr