Efforts to salvage the fishing boat could take days – or possibly longer – with bad weather hampering efforts.

The boat capsized and sank in heavy seas off central Queensland last month, leaving only one survivor. Ruben McDornan, 32, was rescued by a passing vessel after treading water for hours.

Police divers later found the bodies of two of his crew mates, skipper Ben Leahy, 45, and Adam Hoffman, 30, inside the sunken vessel. But four others, Eli Tonks, 39, Adam Bidner, 33, Chris Sammut, 34, and Zach Feeney, 28, remain missing.

Inspector Darren Somerville said a salvage company had started to attach rigging to the trawler, which is at a depth of 30m, to turn it the right way up. After that, more rigging will be needed to bring it to the surface.

Insp Somerville said crews were working slowly to ensure their safety.

“We do hope we can find those four people,” he said.

“Our divers are fairly confident that the vessel has been cleared, however they weren’t able to check underneath the vessel.

“And, obviously, once it’s on the surface, it will be a lot easier to search again – through the vessel, but also where it lies on the seabed.”

Insp Somerville said the trawler would be brought to the surface and towed to shore, where Maritime Safety Queensland experts would help police determine why it sank.

“It’s a tragedy, and six people have lost their lives, but hopefully by finding out why it occurred, we can give closure to the families,” he said.

Insp Somerville said it had been a difficult operation from the start, with bad weather hampering the initial search, and again when work began to bring MV Dianne to the surface.

“We hoped at that early stage we’d find them alive,” he said. “That hasn’t been the case.”