"Without sparing a thought for himself, he stripped out of his uniform, and with the aid of a member of the public wearing a wetsuit, immediately swam out to where the 15-year-old-boy was clinging to his upturned craft.
"Thanks to Constable Davidson's selfless and courageous actions, the boy, who had been in the chilly water for almost 30 minutes, was able to be rescued safely without further incident."
Mr Guthrie said it could have been a different story if Mr Davidson had not acted when he did.
"We could just as easily have been dealing with a tragedy ... "
But for Mr Davidson it was just another day on the job and, after a hot shower and cup of coffee, he was back to work.
"I just did what any other cop would do," he said.
"I was confident I would be able to get out to him so just stripped down to my undies and swam out. I explained that I was a police officer and jokingly apologised that I didn't have my notebook with me, but that the rescue boat was on its way.
"I just tried to provide him with some reassurance and keep him talking until the rescue boat arrived."
Thomas George was returned to shore and taken to Dunedin Hospital for a check-up.
He is understood to be receiving treatment for mild hypothermia, police said.
Despite the teen being well prepared with a wetsuit and lifejacket, and despite him being a fairly experienced young sailor, police said the water was cold and so he would have been in serious trouble if he had he been stuck in the water for much longer.
Mr Davidson commended the member of the public, who jumped into the water with him and swam out to the yacht, for his part in the rescue.
Mr Guthrie acknowledged the help of the Coastguard and other members of the public who had assisted in the rescue.
Neil George, Thomas' father, also attended the incident with students from his class in an inflatable speed boat.
"It's what they call a teachable moment," he said.
He said his son was "fine" despite the ordeal.