I had this idea for ships ranked by numeric class 1-6.
Regardless of a ship's class, all jump drives, aka "hel-cores", are powered by intense bursts of BBN. The regular engines all run on hydrogen fuel.
is ideal for it's abundance and recycle-ability into water and algae,
both of which can sustain the crew for months in the event of a jump
drive breakdown. However, prolonged exposure combined with infrequent
and/or shoddy maintenance can make metal quite brittle. Every pilot can
tell you stories of a ship whose fuel cells shattered, released hydrogen
into the ship's artificial atmo, and blew the whole crew to kingdom
come. "Only a fool neglects his fuel" is an adage commonly heard in
every corner of the galaxy.
Some larger ships can be modified to siphon hydrogen fuel from gas planets, but with the high cost of custom "H scoops" also comes the risk that the ships could be destroyed by the dangerous skimming. Skimming planets involves buzzing their atmosphere and pulling hydrogen into condensers, but doing so exposes the ships to other harmful effects, not the least of which being simple icing of the vents, thrusters, and other such mechanics. If a ship freezes up while skimming a large gas giant, it can easily be pulled into the core depths and crushed by the immense pressure.