I dont know if any1 is aware of this but in each ships sim file is an entery for their tonnage.
Funny enough tho, its under MASS, not displacement !
excert from the C3 sime file:
GC......SD......
mass...hF....gc_height... A....fr_ratio....?....put_on_water..M...Surfaced.. ...displacement.........draught.33.A....drag
It wont effect you tonnage tho since thats taken from the cfg files. I just thought it be a nice lil bit of FYI thingy