A New Zealand father who was missing at sea with his six-year-old daughter on a tiny catamaran for 27 days says he was never in danger and that a broken rudder forced him to sail to Australia.

Key points: Alan Langdon and his six-year-old daughter Que left New Zealand on December 17

Alan Langdon and his six-year-old daughter Que left New Zealand on December 17 The girl's mother hired a child-recovery expert to investigate

The girl's mother hired a child-recovery expert to investigate After 27 days at sea, they arrived in Ulladulla, NSW on Wednesday

Alan Langdon left Kawhia Harbour on a tiny catamaran with his daughter Que on December 17 and said his original plan was to sail north to the Bay of Islands in time for Christmas.

However, he turned up about 2,600km off course in Ulladulla, New South Wales, on Wednesday.

What could have been passed off as an innocent summer adventure took an odd turn when the girl's mother, Ariane Wyler, who is estranged from Mr Langdon, hired a child-recovery service in an attempt to locate the pair.

The six-metre catamaran that Alan Langdon and his daughter sailed to Australia on. ( ABC News: Greg Nelson )

When one of the boat's two rudders broke four days into the trip, Mr Langdon said they had to abandon their plans.

"Once we had no rudder, we didn't have as many options," he said.

"We waited for the fine weather [so we could fix it]. At that stage, we were being pushed south and out. I didn't realise sailing with one rudder was going to be as difficult as it was."

Mr Langdon and Que spent almost four weeks on Mr Langdon's 6.4-metre boat.

He said he had no idea he had been reported missing in New Zealand, and did not realise he would be sailing into a media storm.

On New Year's Day, he decided that heading to Australia would be the safest option.

Alan Langdon and his daughter Que, who sailed from Kawhia Harbour to Ulladulla. ( Facebook )

"I knew we'd arrive somewhere in Australia. I knew we had plenty of fresh water," he said.

"It was just a question of time. I didn't want to push the boat."

New Zealand Police on Wednesday confirmed the duo had arrived at the coastal town, about 225 kilometres south of Sydney, on Mr Langdon's catamaran.

Col Chapman, the Australian child recovery expert hired by Ms Wyler, said he had suspected Mr Langdon would attempt the near 2,600km journey.

"Despite initial thoughts to the contrary and, nothing against the New Zealand authorities, they did think it [the journey] was foolhardy and that no-one in their reasonable mind would attempt it, he did," Mr Chapman said.

It was reportedly the second time that Mr Chapman had been hired by Ms Wyler to look for the pair after he found them living in rural New Zealand more than a year ago.

Map Alan Langdon's journey

He is talking to Australian officials, and New Zealand Police are waiting for more information about Mr Langdon's crossing of the often-stormy Tasman Sea.

But Ms Wyler always thought it was possible Mr Langdon would attempt to reach Australia.

"He knows the sea, he knows the wind, he understands that," she said on Friday.

"He's a very capable man. He's able to fix things as they go wrong."

In a statement, New Zealand Police confirmed they would assess "the background" to the matter before taking further action.

The Australian Federal Police confirmed they would assist authorities in New Zealand.