If the diver had been hit at a slightly different angle, this could easily have been a fatal accident, Maritime NZ Northern regional manager Neil Rowarth said.
"Recreational boaties must understand skipper responsibility.
"Every boat has a skipper, they are legally responsible for the safety of people in and around the boat, and must know the rules of the sea.
"In this case, the skipper was speeding and not keeping a proper lookout."
Whiteman turned his boat around to help the diver, and one of his three passengers called the police. They took the diver to Ti Point wharf where they were met by Police and an ambulance.
"The skipper was inexperienced and had no boating qualification," Rowarth said. "This was his first boat and only the third or fourth time he had taken it out on the water.
"I urge every new skipper to get training and help from a boat club or Coastguard Boating Education. It's not hard, it's not expensive and you get to meet boaties and have some fun learning.
"What you learn makes you, your family and friends, and others in the water safer – and if you see a dive flag, slow down."