I found myself staring a Yor fleet in the face a little while ago and I'd neglected to tech up my hull designs. Fortunately, reinforced hull points added to a standard cargo hull let me create an 11 HP, 4 laser, 2 (something or another) defense ship to hold them off.

At the end, my cargo ship had levelled. So I shrugged and figured I might as well get some use out of it. Half a game later,  I have a level 21, 44 HP cargo ship that's beating the hell out of everything in sight. From what I can tell it's levelling based off its standard 1 HP instead of the true HP totals. Not that I don't mind the ability to create the equivalent of a Large hull at the beginning of the game that also levels like crazy, but it seems a little overpowered.