A fisherman who clung to his upturned trawler for nine hours off the Kent coast survived because he is fat, his relieved family said.
Johny Ronsijn, 60, stripped naked in order to survive his freezing ordeal after the boat capsized in the North Sea.
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He was spotted by the crew of a passing tanker the following morning and eventually winched to safety by a coastguard helicopter.
The boat's skipper, Eric Maeckelbergh, 38, died in the accident on Tuesday night and a Spanish crew member remains missing.
Johny's relieved daughter Celien said: "He got lucky on the right side of the boat, so he did not get sucked under water.
"He was able to cling to the hull but his clothes were soaked and threatened to drag him into the depths.
"To save himself, he had to cut off his clothes."
She told Belgian newspaper Het Laatste Nieuws: "His body temperature dropped to 33 degrees but his blubber saved him.
"He said that everything had gone so fast and he cannot believe he's still alive."
Dramatic footage of Wednesday's rescue operation was released by the Maritime and Coastguard Agency. It showed lucky Johny, from Ichtegem, being winched to safety by the crew of an air-sea rescue helicopter.
He had managed to clamber out of the water after the boat, called Assanat, suddenly overturned at 11pm on Tuesday.
The stricken vessel was spotted at 7.45am the following morning by a passing oil tanker which raised the alarm.
Johny was taken to William Harvey Hospital in Ashford, Kent, for treatment but is now back home in Belgium. A massive search and rescue operation was launched following the discovery of the boat.
Skipper Eric Maeckelbergh, a dad-of-two, was found in the water several hours later but died after being taken to hospital.
Rescue teams ended their search for the third crew member, Spaniard Diaw Babacar, 42, on Wednesday night without success.
It is not yet known what caused the 55ft shrimper boat, which was based at Zeebrugge, to capsize in the calm waters.
The Marine Accident Investigation Branch is looking into the incident before it considers an investigation.
Boat owner Willy Versluys said: "It is very strange that no distress signal was sent.
"Something like that normally occurs automatically when a ship turns. Or as the crew itself observes problems."