They spotted the boat Easy Rider, moored off Ruapuke Island and swam to it. No one was on the boat, but their cries for help were heard about 10pm by boat-owner Rewai Karetai and his wife Gloria Davis, who were camping on the island.
Mr Karetai rowed out to them in a dinghy and towed them to shore.
Mr Karetai and seven others died in Foveaux Strait two months later when Easy Rider capsized and sank.
Mr Bethune said he was steering Extreme One in "sloppy" waves when the large wave hit.
"I didn't see it coming at all."
Ms Zonneveld, of Edendale, a friend of Mr Cullen's, said her sister was visiting from Wellington. Both were keen anglers and accepted an invitation to go fishing that evening.
The sisters were wearing several layers of clothing including thermals and leggings but the men were lightly dressed in jeans, T-shirts and sweat shirts.
Ms Saxton said she was in the cabin when she saw a wall of water "like light blue glass" come across the boat from the right.
The survivors said they knew Shaun Bethune and Mr Cullen were dead when they went blue and became non-responsive during the swim.
Mr Bethune cradled his son before letting him go, Ms Saxton said. Mr Cullen had been swimming between the two women and they made the decision together to release his body.
The bodies of both men were recovered next morning.
Maritime New Zealand accident investigator Ian Howden told the inquest it was well known that rogue waves could "come from nowhere" in Foveaux Strait.
Coroner David Crerar found Shaun Bethune and Mr Cullen died of hypothermia.