Since this is an AU, is it safe to assume perhaps these unmanned ships have the ability to do those things?
A crew of three can fly a huge plane, a crew of one or two can drive a mighty train etc, why not a ship with the same principles?
because an plane or an train gets maintenance when it's stopped. an ship gets maintenance underway.
Indeed, neither of the two are away from maintenance facilities for any period of time (with the slight exception of some locomotives being based further away from their home depots but even then maintenance can be and is done whilst they are not in operation.