Okay a bit of plot spoiling
Sajuuk is really just a dreadnaught on steroids, it's armor is almost twice that of the mothership and it's beamcannon is the most powerfull in the game, it can slice a vaygr cruiser in 3 hits (if the armor isn't upgraded) the only problem I can remember with it is that it can't target fighters.
It's what you and Makaan is searching for throughout the game
For the ultimate spoiling try
http://well-of-souls.com/homeworld/hws/
You can find information about all HW 1, HW 2 and Cataclysm ships here, as well as a few outtakes, some HW 2 ships are a bit vaguely detailed though, I think it's made before the official release of HW 2, there's also a lot about the plot