The S.S. Zelbess is the former S.S. Invincible in Chrono Cross, having been refitted to serve as a cruise and pleasure ship. After the death of Zelbess in Home World, Fargo was unable to reconcile his past actions and instead created the S.S. Zelbess, a pleasure ship that operated around El Nido. It featured a magic act, classy restaurant, casino, and special battle tournament held for monster trainers called the Grand Slam. He rigged the casino, and used the ship to cheat tourists out of their money. When the Black Dragon's dreams started to manifest themselves in Marbule, the Demi-humans eventually left to work on the ship, such as the Demi-Human Innkeeper.
They were exploited and treated as inferiors; even the Sage of Marbule was left to slave as a janitor. Eventually, Serge convinced the Sage to teach the healing song of Marbule to Nikki, and when Fargo from Another World arrived, he renamed the ship the S.S. Invincible (despite Home World Fargo's notes that it couldn't set sail). The Demi-humans subsequently powered the ship to reach Marbule.