He had managed to climb to the top of the upturned hull out of the water.
His family has revealed he removed his clothes in order to survive.
He was rescued when the upside down wreckage was spotted by a passing oil tanker at 7.45am, 17 miles off the Kent coast.
Mr Ronsijn had managed to climb onto the hull, and remained there until he was spotted by the passing tanker.
A second crew member has died and a Spanish fisherman is still missing.
Speaking to Belgian newspaper Gazet van Antwerpen, Mr Ronsijn’s daughter said: “He got lucky on the right side of the boat.
“So he did not get sucked under water.
“He has been 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. “
The Department of Transport’s Marine Accident Investigation Branch is looking into the incident before it considers an investigation.