Gibbons sat on the rear seat behind Turner, who was driving on the left-hand side which is standard for jet boats.
All onboard had consumed alcohol that day.
During their return journey later that night, they reached a section of the river that had a gravel bar in the middle.
Turner saw the gravel island at the last minute and turned the boat to the left. During this manoeuvre, the rear right of the jet boat hit a submerged rock, causing it to roll.
All the group were ejected from the boat onto the gravel island, along with the boat.
Gibbons was trapped by his legs under the boat. His friends managed to pull him out but he had sustained significant injuries and died at the scene.
The post-mortem examination found a fracture of the right knee and that his lower right leg was almost completely amputated.
Turner was charged with operating a ship in a manner that caused unnecessary danger to other persons. He pleaded guilty and on July 22 last year, he was convicted and fined $3000 in the Invercargill District Court and ordered to pay reparation of $20,000.
The legal blood alcohol limit for New Zealand drivers 20 years or over is 50 milligrams per 100 millilitres.
At sentencing, the District Court judge said a blood sample taken from Turneron the morning after the crash was analysed by ESR and found to contain 74mg of alcohol per 100ml.
The ESR estimate at the time of the crash, Turner's blood alcohol level would have been between 130 and 195 mg.
Turner admitted to police he had consumed up to eight cans of beer during the afternoon but said he did not feel intoxicated.
In the coroner's report, Johnson said although Turner was not charged with causing Gibbons' death, his drinking did contribute to it.
"I am satisfied that this evidence before me shows that the level of alcohol consumed by
Mr Turner was one of the two factors that resulted in Mr Gibbons' death.
"Mr Turner's drinking was therefore partly responsible for Mr Gibbons' death and thus contributed towards it.
A report by the Transport Accident Investigation Commission showed it had previously recommended prohibiting people in safety-critical roles being impaired by alcohol or drugs. It's recommendation included people operating recreational vessels.
Johnson said she recommends that the Ministry of Transport reconsiders its current position regarding TAIC's recommendation.
The ministry reportedly responded by saying that although in 2017 the Maritime Transport Act (MTA) was amended to enable drug and alcohol testing in people in safety-sensitive roles in the commercial sector, it has decided not to proceed with such a scheme in the recreational sector.
It said this is because it considers that section 65 of the MTA prohibiting operating any vessel in a dangerous manner included "operating a recreational boat while affected by alcohol or drugs".
Johnson said nothing in the Act provides for an alcohol limit that can guide people to know when they are illegally operating a recreational vessel in a dangerous manner.
"The fact that "enforcement would be particularly complex" should not be a reason for not having a rule in the first place.
"I agree with TAIC that having no legislation or rules specifically to prohibit people
operating recreational vessels being impaired by alcohol or drugs is a safety issue. And I agree with TAIC that Gibbons' death highlights the ongoing risk of not implementing safety actions to address its recommendation."
