I don't think the game gives you enough money to justify maintenance for most to all ships. In GalCiv 2, it was not unusual to get several thousand bc or more a turn, so most ships had maintenance costs. GalCiv 3 and GalCiv 4 are much more money tight, enough so that a few hundred bc per turn was a lot. GalCiv 3 had no maintenance for cargo and tiny hulls. GalCiv 4 is even more money tight, so no maintenance costs for cargo, tiny, small, and medium.
