"Karl's mates, people the family knew and even people we didn't know turned up with their boats to find Karl," said Hugh Earwaker.
"There would have been 50 people out on the water at the start.
"Everyone was deflated when we couldn't find him," he said.
"The input from others was mind-blowing.
"We can't thank everyone enough."
Family and friends were still checking the islands and foreshores on a daily basis - although Hugh Earwaker said everyone was realistic about their chances after this amount of time.
He said it was now about closure.
"We want Karl back so we can put this behind us and move on," he said.
Hugh Earwaker said the situation was totally baffling - apart from being upside down there was no damage to the boat.
"There are no clues as to what went wrong," he said.
He said his son swam on a daily basis and was fit, healthy and competent in the water.
"Karl must have been hurt somehow, maybe flipped by a surfacing whale, or he would still be with us."
The matter has been referred to the coroner.
