I don't know if this has been covered before but…i'm not sure exactly HOW Chaos raiders navigate the warp. the Navis Nobilite isn't exactly available to hire out Navigators to Chaos ships.
My best guess (even if this isn't exactly reflected in the Black Crusade rules) is that chaos ships either use sorcerers to chart a course through the warp or they bind daemons to the ships and have THEM navigate to their target destinations. or they might just punch through the warp and run blind, trusting their fate to whatever chaos god the crew worships.
any thoughts on the matter? feel free to share. i'm considering running a short black crusade game and this is a detail that might be important later.