A five-year investigation into the grounding of a container ship on the Manukau Bar has come up with no safety improvement recommendations.
The Transport Accident Investigation Commission has released its findings into the September 2010 grounding of the 100m coastal container ship Spirit of Resolution.
The ship had left Onehunga Port and the signalman at South Head had observed the waves at the bar approaching the maximum safe bar crossing height of 4m.
The Resolution had almost completed the crossing when the wave height suddenly increased, the ship's speed dropped to almost to zero and it was carried sideways into shallower water.
No one was injured but the rudder was sheared off and there was some damage to the bow and containers.
Crew used the ship's bow thruster to haul it off the bar and it had to wait two days to be towed to New Plymouth.
The report said the captain had enough information to make a decision on whether or not to cross the bar.
There was a wave-rider buoy about 120km south of the harbour which provided information about wave trends, but it wasn't working that day.
Information from that buoy may have informed the Resolution skipper the waves were getting too big, the report said.
However, there was "an element of bad luck" with the timing of the crossing, the commission said.
It looked at whether there should be a wave-rider buoy at the bar.
Ports of Auckland had not tried to install a wave-rider buoy after a navigation buoy and two attempts at a pile beacon were destroyed by rough seas.
The commission said that unless shipping traffic significantly increased or cheaper technology for predicting and measuring wave height was developed, the current system was sufficient.
It noted Pacifica Transport no longer operates out of Manukau Harbour and the other regular shipping service was likely to cease within a couple of years.