Two Queensland men lost in rough seas when their prawn trawler sank should never have been fishing in the treacherous stretch of ocean with such heavy nets, an inquest has heard.

Skipper Matt Roberts, 61, and crewman David Chivers, 36, disappeared when their boat, the FV Cassandra, overturned and sank off the north-eastern tip of Fraser Island in the early hours of 4 April 2016.

The men’s bodies have never been found after huge swells prevented rescuers reaching the stricken vessel, which is believed to have rolled when one of its nets snagged on the sea floor.

Expert witness Barry Ehrke told the Gladstone inquest into the trawler’s sinking the vessel should not have been in the notoriously rough stretch of ocean 10km off Waddy Point.

“In that area there’s a lot of current and there’s numerous hook-ups on obstacles on the bottom,” said Ehrke, who was commissioned by Maritime Safety Queensland to prepare a report into the sinking of the Cassandra.

South-east winds smash into southerly tides and make the water’s surface “disturbed”, the retired fishing boat owner and industry advocate said. In those conditions, he said, the Cassandra’s “quad” net set-up, which hung from the end of its seven-metre boom arms, was too unstable.

Earlier, the inquest heard safety wasn’t a high priority aboard the Cassandra.

An emergency exit had been welded shut for years and an unqualified boatbuilder had been used for a recent refit to get the Cassandra ready for its new life as a prawn trawler.

The boat’s owner had no knowledge about the safety requirements on board and didn’t provide its crew with safety training, the court heard. The vessel’s safety management system also lacked key information for dealing with net “hook-ups” on the sea floor.

A video captured by a remotely operated vehicle used to explore the wreck, which lies upright in waters too deep for divers, showed the boat’s safety gear had failed, the counsel assisting the coroner, John Aberdeen, said.

Automatically deploying life rafts remained attached to the boat, most likely because the Cassandra’s huge nets fell across them as the boat rolled, he said.

The vessel’s two emergency radio beacons also weren’t activated and life jackets were seen on the video floating inside the hull.

The inquest continues on Wednesday.