"We would have been dead," Mr Williams said. "Another two minutes we would have been dead. I literally just collapsed in a heap after it came off. I tried to get up but I couldn't.
"I just think I'm bloody lucky, we all are really."
He and the driver were two of three people on board the boat, travelling along the Ngaruroro River about 3pm when the accident occurred. They had been out on the water since about 10.30am and were "cruising" along in a narrow channel chillingly known as The Graveyard.
In what Mr Williams said felt like slow motion, he spotted the driver being flung 5-10m when the boat hit the bank and flipped. He, too, was thrown into the air, with the boat landing upside down on top of them both.
"I just remember the motor revved and there was a bang and I remember hitting the metal and the boat coming down on top of me. I was flung out of it because I remember it coming down on my back. I was flung out, then the boat ended up on top of me.
"When I was underneath it, I was running out of air. It felt like the boat was getting heavier and heavier."
As he lay trapped, he did not panic but thought he was going to die as he was running out of air and felt as though he was being crushed. He estimates he lay there for up to a minute-and-a-half, before rescuers arrived, pulling the boat off of them and triggering "the best feeling I've ever felt".
While Mr Williams escaped with only bruising, the driver, aged 52, suffered back and chest injuries. Both were flown to Hawke's Bay Hospital. The other passenger, aged 48, suffered bruising to his hips.
While it was a harrowing experience, it had not put Mr Williams off jetboating.
"We are experienced, all three of us are experienced jetboaters," he said from his hospital bed yesterday.
"It was just one of those things really. You didn't know it was going to happen."