He had lost sight of his family, who had also lost sight of him. As Joanne and the children drifted further out to sea, the waves got bigger and bigger, making it harder to stay on the boards, while visibility had also got worse. They were all wearing life jackets – but they had no food or water.
“I had assumed Austin had made it a lot quicker than he had,” she said. “As the day progressed, no vessels and nothing coming to save us.
“If he hasn’t made it, what have I done, have I made the wrong decision, and is anyone going to come and save my other two?”
Austin, meanwhile, had started to swim the last 4km (two nautical miles), abandoning his own lifejacket after a time because it was not helping him.
Throughout the next two hours, it was prayer, Christian songs and “happy thoughts” which kept the “really scared” 13-year-old going.
“I was thinking about mum, Beau and Grace. I was also thinking about my friends and my girlfriend – I have a really good bunch of friends,” he said.
“When I hit the floor I thought, how am I on land right now – is this a dream?”
Then he had another thought: his family “could still be alive out there – I have to go save them”.
It was about 18:00 local time (10:00 GMT) when he finally reached his mother’s bag and rang for help.
The call sparked a huge search, police said in a statement on Monday.
Austin – who had passed out after making the call – was taken to hospital where he called his father, bawling his eyes out. He still didn’t know if Joanne and his siblings were alive.
Then, minutes later, he got a call to say they had been found. Everyone – doctors and police officers – were jumping up and down with joy.
“It was a moment I will never forget,” said Austin.