"We feel unlucky that it happened," Ron Roos said. "But we feel more lucky that we're alive to tell the tale."
Mr Roos (50) was on board a 7m aluminium-hulled boat with old school mates Greg Clark (50), John Turner (50) and another friend, Bill Maitland (55).
"Once we got over the bar, a big wave just popped up in front of us. We weren't expecting it and we didn't have time to turn around.
"The boat just went straight up in the air, we rolled out and the boat flipped over."
Mr Roos said none of them was concerned initially because they were all wearing lifejackets and they were quite close to Taieri Island.
Marine Search and Rescue and the Rescue Co-ordination Centre were alerted and a helicopter containing a water rescue crew was dispatched.
Police and ambulance services from Balclutha, Milton, Mosgiel and Dunedin also attended.
Mr Roos said the four clung to the overturned boat because it appeared to be drifting back to shore.
But concerns began to rise as his three friends got separated from the boat and were swept towards the open sea.
"I tried to swim towards my mates, but I wasn't getting anywhere.
So I tried to swim towards Taieri Island but that was no good, either.
"A helicopter with Water Rescue Squad member Paul Sharp suspended from a rope managed to pick the remaining three from the chilly waters and airlift them to waiting ambulances and police staff on the beach north of Taieri Mouth.
While Mr Roos, Mr Clark and Mr Turner made it to dry land relatively unscathed, Mr Maitland was not so lucky.
Mr Sharp said Mr Maitland had other medical conditions and was suffering from hypothermia.
"He was barely responsive to my voice. He'd been in the water for more than half an hour."
Mr Maitland was flown to Dunedin Hospital in the Otago Regional Rescue Helicopter and remains in a stable condition in intensive care.
"The helicopter guy said another 10 minutes in the water and Bill might have died," Mr Roos said.
The other three were checked by ambulance staff on the beach but were not taken to hospital.
All were feeling lucky.
Marine Search and Rescue adviser Keith Simon said the incident was "another one for the record book" but it was fortunate the four on board did not turn out to be drowning statistics.
"They shouldn't have been out. There's an easterly swell, the tide's going out - it's totally the wrong weather.
"They were the only ones silly enough to venture out."
Mr Simon said the owner and driver of the boat, Mr Clark, owned a house in the area and should have known better than to attempt to cross the bar under the conditions at the time.
However, Mr Roos rejected the criticism.
"I normally get the wind up easily. If something seems dangerous, I'm the first to say, hey. But on this occasion, I wasn't scared at all.
"We went out three days ago in exactly the same conditions and we were fine.
"Greg's very familiar with the bar. He's been over it many times before. We didn't believe it was dangerous at all."
Mr Roos praised Mr Clark for staying with Mr Maitland in the water until he was airlifted to Dunedin Hospital.
He also praised the Marine Search and Rescue crew for their speedy response.
The boat was recovered from the mouth yesterday afternoon by helicopter.
