The crew of the MV Blythe Star had no reason to suspect the 44-metre freighter would join the hundreds of other ships that had disappeared into the depths off Australia's treacherous south-east coast.
It was a fine day, just under 50 years ago, and the water was calm. Then the Blythe Star suddenly listed to starboard and keeled over just off Tasmania's south-west cape.
The 10 crew members made it onto an inflatable raft.
But after nine days on the raft and a subsequent three-day, cross-country trek, only seven survived.
The resting place of the Blythe Star itself remained a mystery until this year — when the cargo ship was found 10 kilometres off Tasmania's south-west coast.
Maritime archaeologists had a hunch about its location; then the CSIRO's Research Vessel (RV) Investigator, en route to study an underwater landslide, confirmed its location.
There are 660 documented shipwrecks along the Victorian coastline, but fewer than half have been found and identified.
The successful rediscovery of the MV Blythe Star has given Victorian archaeologists and historians renewed hope for the more than 300 vessels that remain lost.
Searching the depths
Heritage Victoria senior maritime archaeologist Danielle Wilkinson said historic records proved the ships existed, albeit hidden in the depths.
But the Investigator's suite of scientific wizardry allows historians to find those in the deepest waters.
"Beforehand most of our discoveries were undertaken by divers, and that's limited by depth," Ms Wilkinson said.
"Recreational diving lets you dive to about 30 metres, technical diving to 70 to 80m. Any deeper and you are getting to the limit of what's safe.
"The Investigator can search — using technology — much, much deeper environments … where divers cannot safely access.
"That's why they were able to find one of our shipwrecks, the SS Iron Crown, in 700m of water in Bass Strait."
The Iron Crown was a freighter sunk by a Japanese submarine during World War II.
The Investigator confirmed its location in 2017.
"Sometimes we have a rough idea where these ships go down based on historic record," Ms Wilkinson said.
"What you can then do is provide the CSIRO with rough coordinates and they go to those areas and run their surveying equipment.
"If they see an anomaly — something on the seabed that doesn't look natural — they can then send a camera or ROV [remote operated vehicle] down for a visual, which is what we call ground truthing, to see if it is indeed a shipwreck."
Mapping the ocean floor
The main purpose of RV Investigator's sonar sensors is to map the floor of the ocean, which in turn allows the CSIRO to find bathymetric features such as underwater mountains (sea mounts) and continental shelf slopes. These features are habitats for a rich array of marine life which can be studied by scientists on board.
Ben Arthur is a marine ecologist with the CSIRO but discovering shipwrecks has become an exciting "side hustle".
"My role on Investigator is largely to deliver marine science. Part of that is to understand the sea floor," Dr Arthur explained.
"There's sophisticated technology on board and as well as revealing natural features it can also uncover man-made objects including shipwrecks."
Dr Arthur said the equipment used to map the ocean floor had some similarities to what anglers would call a "fish finder", centring on acoustic systems.
"It sends down beams of sound from the vessel, which travel through the water and hit the sea floor, and what is on the floor bounces back," he said.
"In essence, it's a more powerful version of the systems anglers might have on their 'tinny'.
"It sounds simple but you can imagine what that's like in waters that are many thousands of metres deep. It's quite complicated."
The past preserved under water
If they find something of interest with the sonar, the scientists can deploy a camera system for video identification.
"That's critical in the case of shipwrecks because we can see what it looks like and do things like read the name of the vessel on the side of the hull if it's still there, which is really the best way of confirming what we have found," Dr Arthur said.
Ms Wilkinson said, once wrecks were discovered, a lot could be learned without disturbing them, including details of their construction and even well-preserved artefacts on board.
"Material on board shipwrecks actually preserves quite well under water, particularly underneath the sediment compared with on land," she said.
"[That includes] a lot of fragile materials such as fabrics, lace or leather — so we get a much richer artefact assemblage on shipwreck sites than we do on land sites.
"It's also our role at Heritage Victoria to protect these shipwrecks for the future."
Ghosts of the deep
The 330 missing ships, compiled as part of Heritage Victoria's shipwreck recovery program, covers the breadth of the state's nautical history.
It ranges from tall sailing ships constructed from timber to relatively modern steamships.
One of the smallest is the long boat that was used by survivors of a larger ship, the Sydney Cove, which sank off Tasmania in 1797.
They sailed to Victoria and then walked 800 miles (1,287km) all they way to Sydney.
At the other end of the spectrum is the HMS Sappho, a much larger vessel, which was tasked with relocating Commander Moresby and his entire family (and possessions) to Australia.
Ms Wilkinson said, while many of Victoria's lost shipwrecks would be too deep to find for all but the most powerful scanning equipment, much could still be discovered closer to the shore.
"We only have two maritime archaeologists so Heritage Victoria relies heavily on marine industries such as fishing and the public for discoveries," she said.