There's a mystery shipwreck at the bottom of the Halifax harbour that's baffled researchers and scientists for years.

The schooner's origin, even its name, are unknown. But a marine geologist who helped map the harbour bottom believes it was sunk on Dec. 6, 1917, by the Halifax Explosion.

What's left of the shattered steam-powered vessel sits in 28 metres of water, partially buried in silt, and covered in rust and marine growth.

"It's a copper-clad schooner," said marine geologist Gordon Fader.

Fader helped discover the mystery vessel in 2002 when he worked for the Geological Survey of Canada at the Bedford Institution of Oceanography — he was part of a team using sidescan sonar to map the harbour's sea floor.

A closeup photo of the bow of the mystery schooner. (Dana Sheppard/Heritage Dive Team )

After it was spotted, divers went down to get a closer look.

"They said it also had some very expensive additions to it," said Fader. "In other words, all of the fittings and the equipment on the deck were high quality brass and other high quality material. So we were wondering perhaps maybe it was a naval vessel or somebody who seemed to be very rich."

The British Royal Navy started using copper plates in the 18th century to protect ships from the corrosive effects of the sea and from the accumulation of critters that might damage the vessels.

Outfitting a schooner in copper and brass was an expensive proposition, and losing such a vessel would be incredibly costly. Yet no records exist detailing the schooner's sinking.

That's left Fader to come up with the theory that it was sunk during the Halifax Explosion.

"We were very sensitive after the explosion about ship traffic and events in the harbour," he said, which leads him to believe the vessel didn't go down in the years after the explosion. "I'm sure it would have been in the papers and we would have all known about it."

This is the sidescan sonar image that discovered the vessel. (Royal Canadian Navy Fleet Diving Unit)

Researchers tried to track down the origin of the schooner shortly after it was discovered in 2002. Jim Camano with the Heritage Dive Team wrote a report outlining their research.

In the report, Camano said the wreck was found about 100 metres away from the Halifax Shipyard.

Through his research he narrowed the mystery vessel down to two possibilities, the St. Bernard and the Lola R.

Both vessels were believed to have been lost during the Halifax Explosion.

No blueprints or drawings of either were found but researchers were able to tease out a few vessel specifications.

Camano and the other researchers don't think the mystery schooner is the St. Bernard, since that vessel was 27 metres long and the ship at the bottom of the harbour is only about 12 to 16 metres.

Researchers said the Lola R had little in common with the mystery schooner, aside from being about the same length. There was also no mention in any records that the Lola R was steam powered.

The St. Bernard was a lumber schooner. (Nova Scotia Museum)

After a year and a half of research and diving, the team concluded they could not identify the vessel.

However, they were able to say the schooner was expensive to build because of all the copper and brass components. It was also built light for speed.

Researchers thought it unlikely the vessel was a tug or commercial ship, but it did have many features suggesting it may have been a navy ship.

A close-up photo of the starboard side of the hull. (Jim Camano/Heritage Dive Team)

The report was completed in 2004. Since then, Fader said very little work has been done to identify the mystery schooner. But he's optimistic.

"Like all things in Halifax harbour, the last word hasn't come out on many of the shipwrecks and the history. The bottom of the ocean holds lots of secrets," he said. "However, with our new modern technologies and the will, people are always discovering new things."