Murray Wakefield said he was returning to the yacht berthed at Careys Bay about 5pm on Sunday.
While descending a ladder from the jetty to the keeler, he slipped and fell into the chilly harbour water.
He manoeuvred himself around to the ladder at the stern of the vessel, but was unable to haul himself up.
"It was tough ... I was just hanging on for dear life."
Wearing heavy work boots, he remembered kicking the propeller in desperation as hypothermia set in.
Mr Wakefield believed it was about two hours later when Port Otago’s pilot boat Potiki motored into the bay.
Captain Shree Paranjpe said he and his crew, consisting of launch master Ian McLean and deck hand Frank O’Neil, first thought the cries for help could be children fishing near Boiler Point.
But upon shutting off their engine they realised the yells were something more serious.
They rushed around to the end of the jetty and saw a man clinging desperately to a yacht, then rushed back to their launch before steering it alongside, hauling him out of the water and wrapping him in a blanket.
As he lacked the strength to climb up a ladder, they motored around to the tug mooring area where emergency services were waiting, before a chilly but grateful Mr Wakefield was taken by St John ambulance to Dunedin Hospital to be treated for severe hypothermia.
"We were really, really pleased — gosh it was a lucky thing," Capt Paranjpe said of the fortuitous rescue.
"Such a lovely feeling."
Feeling a bit the worse for wear but in otherwise reasonable nick, Mr Wakefield said he was extremely thankful for the help of the pilot boat crew.
"They saved my life, man."
His yacht was not normally berthed at the jetty, but his other boat was at present occupying his usual mooring, he said.
The 48-year-old, who works in the forestry area of Port Otago, said his boss had agreed to give him yesterday’s shift off, and he was planning to take it easy and recover from the experience.
"Just put my feet up."
