He swam against the tide for more than an hour, broke two toes and ran on rocks and barnacles to get help to save a drowning friend - but Terence Gosnell says it's his friend who is the real hero.

The ordeal for Mr Gosnell and fishing partner Colleen Herrick began when their boat hit a semi-submerged log on the northern side of Motuihe Island in the Hauraki Gulf about 4.30am on Thursday.

Mr Gosnell, 42, who lost his 5-year-old brother in a boating accident in 1975, said it was Mrs Herrick's calmness that saved their lives.

After the 4.8m boat sank in 10 to 15 seconds, Mr Gosnell decided to swim to the island to raise the alarm and get help to Mrs Herrick, who was clinging to its side.

"I looked up at the heavens at one point - believe it or not - and said: 'Oh God, you can't do this to me twice in my life - losing two people I care about'," he said. "The last pocket of air in the nose of the boat was almost gone, with both of us holding on. But Colleen remained amazingly calm.

"We made the decision that because I was the stronger swimmer, I should go for help."

Mr Gosnell, of Glen Innes, said the icy water had numbed his body, so he did not feel the pain running with two broken toes and being cut by rocks and barnacles. "I've cut my feet to bits, hands to bits - I shredded myself running for help. Every part of my body feels like it's gone through a mincer. I've collapsed a few times, but got up. I didn't care because I had to save my friend."

He ran for about a kilometre after reaching shore before finding a ranger, who raised the alarm.

Meanwhile, Mrs Herrick, 53, said she counted stars and thought of her eight grandchildren - the youngest of whom just turned 1.

Mrs Herrick and Mr Gosnell, both followers of the Ratana faith, have known each other for more than 35 years and have been out fishing together more than 500 times.

"I wasn't afraid because I had faith in God and I had faith in Terence," Mrs Herrick said. "I knew he would do everything to save me."

Mrs Herrick was eventually found by the Mechanics Bay-based Marine Rescue Centre and picked up just over an hour after the boat sank.

She was taken by ambulance to Middlemore Hospital and treated for hypothermia.

"It was tearful just waiting for the rescuers to come back," Mr Gosnell said.

"When they came back and I asked if she had been found alive - they said yes - I just broke down. All that had been worth it.

"Everyone is telling me I should buy a Lotto ticket. I'm just glad to have my friendship intact - that's all the reward I need."

- additional reporting by Vaimoana Tapaleao