An investigation has laid blame on both anti-whaling vessel Ady Gil and Japanese whaling ship Shonan Maru No. 2 for their Southern Ocean collision earlier this year.
The Ady Gil was on a Sea Shepherd Conservation Society mission aimed at stopping Japanese whaling when it crashed into the Shonan Maru on January 20.
The impact tore off 3.5m of the Ady Gil's bow and left a cameraman aboard the trimaran with a suspected fracture to his rib.
The boat's skipper, conservationist Peter Bethune, was later put on trial in Japan after trying to make a citizens arrest of the Shonan Maru No. 2 captain.
A Maritime New Zealand investigation has found both vessels disobeyed international anti-collision rules for "close quarters" encounters.
Neither the Shonan Maru No. 2 captain or Mr Bethune were charged with deliberately causing the impact.
"The collision appears to have resulted from a failure on the part of both masters and the crew of both vessels to appreciate and react appropriately to the potential for collision," the report says.
The report says the Shonan Maru No. 2 kept at an unsafe speed and turned starboard to put itself in a collision course with the Ady Gil.
As the overtaking vessel, the Shonan Maru was responsible for avoiding a collision and had sufficient room to do so, the report says.
The report says is near certain the ship's captain knew the Ady Gil was there and did not adjust his course despite having "ample opportunity".
But the report criticises Mr Bethune and his crew for not keeping a good lookout and contributing to the collision.
Mr Bethune should have kept well clear of the oncoming whaling vessel, but instead maintained his course and speed, the report says.
Its helmsman did not monitor the ship's radar and left himself little time to take evasive action, it says.
Investigators found there was insufficient evidence to say whether the Ady Gil's helmsman's acceleration of the ship before impact contributed to the crash.
Mr Bethune says he accepts the reports findings and has moved on from the incident.
He has retracted an earlier statement that the collision was "attempted murder" on the part of the Shonan Maru No. 2 captain.
"Having been on the Shonan Maru and met the crew, they're just doing a job. I've met the captain. One day I could see myself sitting down and having a beer with him."
But he remains adamant the ship turning in "the last 10 seconds" to adopt a collision course was a deliberate attempt to damage the Ady Gil.
"If they didn't mean to murder us, they certainly meant to damage out vessel."
He has no regrets about his actions in the Southern Ocean.
"In the end it was just a boat and I have six guys here who are happy to be alive.
"In many regards the sinking of the Ady Gil has done more for stopping whaling than anything else we could have done there.
"Whaling is a big issue in Japan now. It's put the spotlight on the issue."
Maritime New Zealand says the incident shows the need for all vessels to act responsibly in the Southern Ocean.
In its report, its director:
a) reminds all masters of the need to comply with the International Collision Regulations, the domestic laws and regulations of their flag state and the practices of good seamanship, irrespective of the activities they may be engaged in
b) calls for a higher standard of care to be taken by all parties who may be involved during demonstrations, protests or confrontations on the high seas
c) denounces actions or inactions that could potentially endanger human life, the marine environment or property during demonstrations, protests or confrontations on the high seas
d) draws the parties' attention to the IMO's resolution assuring safety during demonstrations, protests or confrontations on the high seas.