Barge is pure win, bump it and as it flips it will simply massacre any ship it bumps (saw a barge flipped by NPCs instakill a poor freighter a few days/a week ago....
Barge + pirate ID; Give me your cargo or my mate here will bump my ship...
Barge should gain epically fast turning, but just horrid turning while in speed (if that is possible)
It is balanced perfectly fine for what it is intended for. Yes, being treated like a pinball by ships one tenth the size of yours is annoying. That isn't a balance issue, that is a game mechanic issue.