A boat ran aground on Rangitoto Island in the Hauraki Gulf yesterday while on autopilot.
A female passenger received serious wounds to her head, neck and ribs and was knocked unconscious, while her male companion badly injured his ribs but was able to walk from the boat. It's believed the 9m Bayliner Chindit was travelling at 26 knots on autopilot when it mounted the rocks between the wharf and Islington Bay at around 1.30am.
Coastguard Duty Officer Mike Lawrence says events leading up to the unusual crash are unknown.
The couple, who had lost their cellphone, spent five hours stranded, letting off flares in an attempt to attract attention. "It was just too early for anyone to notice them," Lawrence said.
Police were notified at 6.15am. Both passengers were taken to Auckland Hospital. A coastguard assisting at the accident site was taken to hospital with a lacerated hand after he slipped on rocks.