Mark Allan, 35, had drunk 10 cans of lager when he offered to take Harvy D’Silva on an “adventure” close to their home at Brompton-on-Swale, North Yorkshire, last Easter, but the escapade ended in tragedy.
The pair capsized the recreational dinghy in the River Swale and the boy grasped hold of a branch in the fast-flowing water.
Mr Allan had got out of the water but went back in to save the teenager, probably exhausting himself in the process, the inquest in Colburn, North Yorkshire, heard.
The boy ran home in 10 minutes and got in a hot bath, after Mr Allan told him to go and that he would follow him.
But the delivery driver was found dead, having suffered from hypothermia, by a search and rescue team at 9am the next day, four hours after Mr Allan’s partner Kursten D’Silva had contacted police.
Coroner Rob Turnbull heard she did not tell police her son had been with Mr Allan because they did not want Mr Allan to get in trouble for taking a teenager out on the dangerous escapade.
That had led to an acrimonious split between Mr Allan’s close-knit family and Ms D’Silva who has a two-year-old daughter by him called Boo-Betsi.
They felt by not telling police of her son’s involvement, the searchers were denied information which could have led to Mr Allan being found more quickly.
Mr Turnbull recorded a verdict that the death was an accident.
He said: “Mark is described by all who knew him as a person who lived life for the now, known to do eccentric things from time to time.
“Clearly he was well-loved by everybody.”
Mr Allan and Ms D’Silva had both drunk heavily that evening and they allowed Harvy to stay up late.
She fell asleep downstairs and did not know Mr Allan was taking her son out in the pitch black on a dinghy.
Harvy told the inquest: “Obviously the consequences would be really bad, at the time it was a really awesome idea.”
Mr Turnbull said Middlesbrough-born Mr Allan was later found to have been hypothetically one and a half times over the legal drink-drive limit.
Pc Martin Usher, who first searched for the missing man, was an experienced kayaker and estimated the river speed to be 15-20mph.
“It was absolutely treacherous,” he told the inquest. “There’s absolutely no way I would take any form of water craft down that river.”
The coroner said: “It was not until some time later that Harvy told other members of the family exactly what had happened.
“That was withheld from the police for a considerable period of time.
“The fact is that members of Mr Allan’s family knew what happened, for reasons I cannot understand no one told the police.”
Mr Turnbull said it will never be known if withholding the information made a difference to the outcome.
“He did die as a consequence of taking a dinghy out on the river with Harvy and the fact it overturned,” he said.
“If that had not happened, everything else would have been irrelevant.
“This clearly was a tragedy, it shouldn’t have happened.
“The reason it happened really stems from Mark’s decision to take that dinghy out.
“He is clearly a tragic loss to all who loved him.”
His parents Bill and Barbara, from Richmond, said in a statement afterwards they were “blessed to have had such a wonderful son”.
“Mark was a unique, unconventional person who enjoyed life and lived it to the full,” they said.
“We miss Mark every day and always will but the fun and memories will be with us forever.”
They thanked the search teams for their rescue efforts.