The Mars sank in 1564. It was at the time perhaps the biggest ship in the world—a fearsome vessel with over one hundred guns and 700 men onboard. The Mars met its end in a bloody sea battle between Sweden, which had built the formidable warship, and the combined armies of Denmark and the German province of Lübeck. During the battle, the Mars caught fire but, despite the clear danger, the Mars was still boarded in its last minutes by enemy forces. The flames ignited the gunpowder stored on the ship causing a huge explosion that blew out the stern of the ship and took her, and the men aboard her—the Swedish sailors and invading forces alike—to the bottom of the ocean. Why was she boarded at such a dangerous time?
One suggestion was that the boarders were desperate to recover the thousands of valuable silver and gold coins the ship was said to carry, even if it meant risking—and ultimately losing—their lives.
Johan Rönnby, head of the MARIS research institute at Södertörn University set up to study the Mars, said, "Mars is a legendary ship in Sweden, and almost everybody wanted to find it. It was built by the King Erik the XIV, who was son of Gustav Vasa—Vasa is our Tudor dynasty. The ship is connected to the building of Sweden. Sweden had become a country, and there was an attempt to make Sweden a European superpower and Mars was part of that concept, really. Erik had built maybe the biggest ship in the world in the 1560s, so Mars was a special ship. She was more than 60 meters long and very modern-equipped."
The conditions in the Baltic Sea—the temperatures and absence of shipworm, which can destroy submerged timber—mean any ships that have sunk in its waters are often well preserved. Over the course of Ocean Discovery's search, the team had found tens of wrecked wooden ships maintained in a good state by the Baltic waters, located using the trawl snag data from the fishermen, but none had been the Mars.
One suggestion was that the boarders were desperate to recover the thousands of valuable silver and gold coins the ship was said to carry, even if it meant risking—and ultimately losing—their lives.
Johan Rönnby, head of the MARIS research institute at Södertörn University set up to study the Mars, said, "Mars is a legendary ship in Sweden, and almost everybody wanted to find it. It was built by the King Erik the XIV, who was son of Gustav Vasa—Vasa is our Tudor dynasty. The ship is connected to the building of Sweden. Sweden had become a country, and there was an attempt to make Sweden a European superpower and Mars was part of that concept, really. Erik had built maybe the biggest ship in the world in the 1560s, so Mars was a special ship. She was more than 60 meters long and very modern-equipped."
The conditions in the Baltic Sea—the temperatures and absence of shipworm, which can destroy submerged timber—mean any ships that have sunk in its waters are often well preserved. Over the course of Ocean Discovery's search, the team had found tens of wrecked wooden ships maintained in a good state by the Baltic waters, located using the trawl snag data from the fishermen, but none had been the Mars.
The sidescan sonar is the best technology available, but it's not so detailed that you can see cannon and things," said Lundgren. "It's more technology for locating, not for marine archaeological survey."
Having spotted the wreck, the team sent down an ROV for a closer look. "The camera quality on the ROV is quite poor. We did see the intact hull side but we didn't see any gun ports. We were filming for an hour but we didn't see any cannons. Navigating an ROV on a complex wreck site like that is hard. It's very three dimensional, there's wood sticking up, and the umbilical from the ROV can get tangled. The ROV surveying couldn't prove it was the Mars, it could only prove it was a large warship," Lundgren added.
Absolute confirmation would require human divers
"In 2012, we made a photo mosaic of the whole site with 600 pictures put together. It's at 70 meters depth, it's totally, totally dark in the Baltic Sea. It's a tricky case to work on. You need to take diving technology and rebreathers and a lot of lamps, of course," said Rönnby.
Using sidescan sonar and multibeam sonar, the project began to build up a high-resolution three-dimensional picture of the wreck too.
Multibeam sonars can be either mounted on the underside of a ship or on an ROV and, by emitting sound waves and recording how long and from what direction they bounce off a surface and return, can build up a 3D picture of the sea floor.
The project is also working with a BlueView sonar scanner from MMT, which when positioned on the seafloor can gather 60 million measurement points in 15 minutes. Combined with the million photos taken by divers, a map that's precise to two millimeters has been built up—higher resolution than the multibeam. In time, however, the BlueView point cloud will be merged with that from the multibeam sonar so the two technologies can fill in any gaps from each other.
Having spotted the wreck, the team sent down an ROV for a closer look. "The camera quality on the ROV is quite poor. We did see the intact hull side but we didn't see any gun ports. We were filming for an hour but we didn't see any cannons. Navigating an ROV on a complex wreck site like that is hard. It's very three dimensional, there's wood sticking up, and the umbilical from the ROV can get tangled. The ROV surveying couldn't prove it was the Mars, it could only prove it was a large warship," Lundgren added.
Absolute confirmation would require human divers
"In 2012, we made a photo mosaic of the whole site with 600 pictures put together. It's at 70 meters depth, it's totally, totally dark in the Baltic Sea. It's a tricky case to work on. You need to take diving technology and rebreathers and a lot of lamps, of course," said Rönnby.
Using sidescan sonar and multibeam sonar, the project began to build up a high-resolution three-dimensional picture of the wreck too.
Multibeam sonars can be either mounted on the underside of a ship or on an ROV and, by emitting sound waves and recording how long and from what direction they bounce off a surface and return, can build up a 3D picture of the sea floor.
The project is also working with a BlueView sonar scanner from MMT, which when positioned on the seafloor can gather 60 million measurement points in 15 minutes. Combined with the million photos taken by divers, a map that's precise to two millimeters has been built up—higher resolution than the multibeam. In time, however, the BlueView point cloud will be merged with that from the multibeam sonar so the two technologies can fill in any gaps from each other.
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