Jamie Stephen Boniface was 28 when he went out fishing with friends James Anderson and Nathan Gorton at the Riverton estuary on September 9, 2018.
The three men were in a motorised dinghy that spun around 180 degrees while Mr Anderson, who piloted the boat, appeared to be accelerating along a plane.
The three men were thrown into the water before the boat capsized.
While there were three life jackets aboard the dinghy, none of the men were wearing one at the time they were thrown from the boat.
They were all wearing long gumboots.
In her report, coroner Heather McKenzie said after the dinghy capsized, all three men surfaced about the same time — almost within arm’s reach of each other.
"Mr Anderson and Mr Gorton grabbed the front of the dinghy which was above the water," she said.
"Mr Anderson yelled at Mr Boniface to ‘get his gear off’ and he and Mr Gorton removed some of their clothing."
At this time, Mr Boniface started to swim to the shore which was about 100m away.
It was after a witness heard a man call to Mr Boniface to take off his gumboots that he went under the water and did not resurface.
Mr Gorton attempted to swim to Mr Boniface, however the current was too strong and he lost sight of him.
Mr Boniface was located by divers on September 12, 2018. He was fully clothed but was not wearing gumboots.
Ms McKenzie said while Mr Anderson stated he had consumed two beers while on the boat, there was no evidence he was affected by alcohol — there was also no evidence that the behaviour of Mr Boniface or Mr Gorton had caused the boat to spin.
Mr Boniface’s blood alcohol level was 116mg and there was indications of cannabis use in his system, however there was no evidence that these affected his ability to swim to shore.
It was reasonably possible Mr Boniface’s chances of survival "would have materially increased" had he been wearing a life jacket, Ms McKenzie said.
She said it was reasonable to infer someone wearing gumboots which filled with water would be weighed down.
"In many circumstances, particularly where the water is over the person’s head and water conditions might be challenging such as due to the current or swell, I consider it possible that it would be difficult to remove gumboots in the water."
She recommend that gumboots not be worn on boats of less than 6m.
