Interesting stuff jayman38. I guess is what need is ship class to mass guide like frigates are this mass battleships are that mass, like an eve online system.
There isn't one. At least there is nothing that comes anywhere close to being agreed on. Some servers have official classes, some factions use their own systems, and some people think the whole question of sizes and classes doesn't matter at all.
I don't know if nameless is still around, but Ragnarok uses his system. Some people base it on mass, some on keel length, some seem to have no system or use the ships appearance and shape alone to determine type/class. Calibri made a system that uses filesize to determine class. There's three options here:
http://www.starmadewiki.com/wiki/Ship_Classification but also at least ten more if not 100 floating around, all differing to degrees from tiny to insane.