The owner of the burning boat, John Walker, who survived the fire but was airlifted to hospital with serious burns, was trying to get help.
"I heard some yelling and then [Mr Walker] came and knocked on my window. He was badly burned all up his face and his arms and hands were just all black.
"He wasn't knocking, he was banging and he was yelling that his friend was on the boat.
"He was saying '[my friend] is on the boat'. He was pretty well just repeating that. He looked disorientated and obviously distressed."
The tide was out and the boats were on the sand at the time.
Mr Foster-Christie, an apprentice boatbuilder, jumped out of his window with a small fire extinguisher but quickly realised it would be insufficient.
"It was too late. The doors were open, fire and smoke were billowing out. You couldn't see anything.
"I only had a 1kg extinguisher, you would have needed a 20kg extinguisher, at least."
By this stage Mr Walker, thought to be a lifelong Waiheke Island resident in his mid-50s, was lying on the beach being treated by other people who had seen the fire and stopped.
Mr Foster-Christie said he was conscious and screaming in pain.
Mr Walker is believed to have been living in the boat near the Waiheke Boat Club in Putiki Bay for only a few months.
Detective Inspector Scott Beard said officers had been unable to speak to the injured man because of his injuries.
The cause of the fire was still being investigated.
"At this stage it is unexplained, but we have a police investigation team over there and until the scene examination has been completed, until we have a post-mortem examination, we can't say exactly what has happened," he said.
"We're interviewing local residents, people who are living on the boats around where the boat was itself, and anybody who can assist over on the island."
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