After finishing up, without thinking he connected the two exposed wires to turn the pump back on, but before he realised his mistake it was too late.
A spark jumped from the connected wires and landed in the engine bay, prompting an explosion which engulfed the engine bay and left Wills in flames.
"When it went off I thought 'what have I done'. When it exploded I sat there with dumb amazement, there was a fire above and below the engine.
"I looked down at my legs and it was peeling off in large sheets, one was so big it could cover a tissue box," he said.
He said he could feel no pain - that came later.
At that moment Wills did not believe he could survive the flames.
"I thought shall I sit here and burn? I thought I may as well try do something. I thought of my kids in Australia, my girlfriend and the poor fellow who built the boat."
He managed to stand, shake off the flames and make his way to the cabin, where he doused his still-burning hair.
Peter Wills during his recovery in the Middlemore burns unit. Photo / Doug Sherring
No longer ablaze, he said he caught a glimpse of himself in a mirror and saw his charred face staring back at him.
He spied the fire extinguisher on the boat and made his way back to the blaze in the engine bay to douse it.
Being a former volunteer firefighter in Victoria in Australia definitely came in handy, he said.
"The danger was just starting when I realised what I had done to myself, I climbed out through the hatch, I had a mate 100m over on another boat and called to him, then he was on his way.
"I crawled back in the boat and turned on the shower and started peeling the skin off me before the shock hit."
After a few minutes, his friend made it to the boat and gave him some pain relief which was enough to make him believe he could survive the ordeal, he said.
"I thought there might be a chance. I thought of the Westpac crews, I know that they can keep a dead man alive."
He said he closed his eyes, hung on tight and listened to his heart pounding.
An Auckland-based Coastguard rescue crew found him wrapped in a duvet sitting in a ball after a long, cold shower.
The Senior Coastguard volunteer Chris Griggs said the first priority was giving Wills more pain relief, as it was so intense he was struggling to speak.
Coastguard volunteer Chris Griggs, left, was one of the first rescuers on the scene to aid Wills after the explosion. Photo / Doug Sherring
"He was squatting down, a ball of pain effectively. It was a very disturbing sight."
However, after the pain relief Peter was able to tell the crew where his burns were and which areas were most painful.
"It went from one life-threatening situation to potentially leading towards another. From being really burnt and to being moderately hyperthermic and heading towards severe hypothermia."
Losing so many layers of skin, he became cold after being in the shower. So he was wrapped nearly completely in a duvet to prevent hypothermia.
While moving him off the boat Griggs caught sight of the burns on Wills' back.
"I was behind him and could see the flaps of skin that had come away from him, just peeling off and hand-span sized pieces, too."
He managed to catch up with Wills on Monday night and was told he'd suffered burns to 28 per cent of his body. However, the full damage would only be known later in the week once his bandages came off.
He said Wills was blaming himself for what happened but Griggs praised him and the neighbouring boaties for the initial treatment of the burns.
