The main character in Star Trek
is not the starship, since there have been series in which the Enterprise
does not appear. If you mean any old starship, including Voyager
and the Defiant
, those are still just stand-ins for Starfleet.
As long as its a Starfleet ship, then yeah, we're good to go. If the main character ship is a garbage scow piloted by Harry Mudd, is that still Star Trek
? Not for my money it ain't. The definition is pretty flexible but not that flexible.