My ship has five Navigators - a master that supervises and pulls off the hard bits, three journeymen that do most of the routine 'shift work' of navigating, and one apprentice that works directly at the master's side.
We also have six Astropaths - five that are part of the AAT and send/receive the usual info, and one Watcher of Dusk (PC) that stands outside them as the Lord-Captains personal psyker. There are some bad feelings both ways between theses groups, but the AAT do their jobs faithfully and the Watcher stays out of their way and keeps to the shadows.
I really like this dynamic. Its full of the possibitly of tension and empowers each pc. But if the roles need to be fleshed out by NPCs it leaves and invites all sorts of plot lines and interesting drama. Love it.
Er we go! Git da Humies! Choot em! Chop em! Waaaagh!!