In Auckland District Court today, Fullers pleaded guilty to failing to ensure seats were sufficiently stable "that it would not harm passengers if the vessel stopped suddenly, moved significantly or impacted another object".
Charge sheets attribute the crash to the Kea's "digital control system".
In court today, Fullers also pleaded guilty to operating the ferry with "inadequate risk-mitigation procedures" while faults in its control systems were unresolved.
It is alleged the company adopted risk-mitigation procedures three months before the crash, which meant manual controls were to be used until the control system was fixed.
They were allegedly not followed.
Other charges but they were dropped.
Belmont resident Judy Rhodes, who was aboard the Kea at the time of the crash, told the Herald she was surprised to hear the allegations about defective digital systems on the ferry.
"You put your life in their hands and trust them to do the job they're supposed to do," she said.
"If you've got a faulty car, would you drive it?"
Fullers chief executive Doug Hudson has said he would not comment on the case while it was before the court but stressed they had complied with Maritime NZ.
The Kea has been repaired and back in service since the end of July last year.
Fullers is due back in court for sentencing on April 8.
Maritime NZ prosecutions
2011-12: 14
2012-13: 13
2013-14: 11
2014-15: 11
