The Barbarous was a ship in the fleet of Rabid Jack, an infamous pirate lord of the recent Fifth Age. During a cutscene in Rocking Out, Bosun Giles suggests that the Barbarous was being engulfed in heavy flames by the end of the Battle of the Archipelago.
The Barbarous was one of many ships in Jack's fleet, which he used to prey on merchant, military, pirate, and transit vessels following his failed attempt to capture Mos Le'Harmless. His attacks became so frequent and brutal that the Customs and Exise Office launched a massive anti-piracy campaign that left the other pirates of the Eastern Sea unable to survive.
The pirates of Mos Le'Harmless, unable to cope with both Jack and the Customs Office, attacked Jack's base in the Cursed Archipelago, a chain of uninhabited islands in the southern Eastern Sea. Here the Barbarous played a major role in defending Jack's fleet, although its captain and appearance remain unknown.
The ship was presumably fell to fire by the end of the battle, although had it survived the pirates of Mos Le'Harmless would have burned it to hide any trace of Rabid Jack. However, recent instalments in the pirate quest series suggest the Barbarous may have recently returned from the dead along with the rest of Jack's fleet.