What makes a Carrier? (ftfb)

I've just had a thought about the definition of a carrier in the new
FTFB.

With all the ships I've designed so far using the construction system,
after all the _fixed_ systems (% of mass systems) are installed (drives,
hull, ftl, screens) most ships usually have about 30% of their mass
available for offensive systems & armour.
As a guide, this should make any ship with more than 15-20% of their
mass in fighter bays a carrier (using the old 50% systems definition).	

By the way, try this for a ultralight escort carrier:
Mass: 90 (318 pts + fighters)
Hull: Weak
FTL: standard
MD: 4
Armour: 2
Hits: 18; 5/5/4/4
Crew: 5; 4/4/4/4/2
ADFC
5 Point Defence Systems
4 Fighter Bays

'Neath Southern Skies
http://users.mcmedia.com.au/~denian/