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nuts & bolts

Saving the Vasa ship from rust

Publicerat fredag 11 mars 2011 kl 14.55
"There is a lot of corrosion inside the holes"
(6:27 min)
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Vasa carpenter Monika Ask holding one of the new stainless steel bolts in her hand. Over 5,000 rusty bolts need to be replaced with rust-free ones. Photo: HENRIK MONTGOMERY / SCANPIX
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The tool that Ask uses remove one of the old bolts uses five metric tons of pressure. Photo: HENRIK MONTGOMERY / SCANPIX
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The royal Vasa ship sank on its maiden voyage in 1628 but was salvaged 333 years later in 1961. It has been a challenge for preservationists ever since. Photo: HENRIK MONTGOMERY / SCANPIX

Barely a kilometer into its maiden voyage, the royal Swedish Vasa warship was on its way to Poland when it sank in the Stockholm harbor nearly 400 years ago. It was dug up from the bottom of the sea in the early '60s, and has become one of Scandinavia's most famous tourist attractions. But maintaining the ship is a big challenge for preservationists.

Now, even the bolts that the original conservationists used to keep the giant warship all in one piece have rusted, threatening the surrounding wood. So, on Thursday, just in advance of the 50th anniversary of the ship's salvage, the museum began the long process of replacing the old bolts with shiny new ones intended to fix the problem.

BOLTS LIKE GIANTS' BONES

A carpenter named Monika Ask stands atop a red Skylift, which has her hoisted about two stories up in the air of the Vasa museum. She's hovering by the port side of the old warship, while another worker peers out from a porthole. Suspended from the ceiling, a giant metal jack – bigger than Ask, herself, – is poised in the air. She guides it over to the ship, and uses it to extract something from the ancient wood.

Ask sends down the jack, which kind of resembles a huge screwdriver with the head of a vaccuum cleaner, to an engineer with a braided beard, Anders Ahlgren. He's waiting down below on the museum floor, behind a red and white striped ribbon indicating the work area. From the jaws of the jack, Ahlgren carefully draws out a long rusty piece of metal – nearly the size of a walking stick. This is one of more than 5,000 old bolts that the Vasa museum intends to replace with stainless steel.

Ahlgren compares the old and new bolts. In his hand is a shiny new one. At his feet is the old one, which looks like the leg bone of a giant. It’s tagged with a plastic label: no. 344.

“It’s a more simple construction, the old one,” says Ahlgren. “The new one has several parts, but it’s also lighter,” he adds.

Ove Olsen, a conservation technician, in the ship helping the carpenter change out the bolts. He explains that after the rusted bolt is removed, the hole needs to be widened a bit, because the new bolts are ever so slightly thicker. He also has to clean out the corrosion that the old bolt left behind in the hole. Then, he uses soap to lubricate the hole and make way for the new bolt.

"REAL MONEY" NOT INVOLVED

“The research has shown that iron is a catalyst in the chemical process degrading the wood,” says Magnus Olofsson, the head of the Vasa’s department responsible for the ship's preservation. “And we wanted to get out as much iron from the hull as possible. The bolts are a big part of the iron in the hull, so we started trying to see how we could replace the bolts.”

The process could take more than five or six years, during which the museum will remain open for visitors. By the museum's estimation, they can change out 10 bolts a day, but some will take longer – all the bolts are a little different, and some are situated in more difficult places than others.

Olofsson acknowledges that there is a slight risk that the new bolts will cause unwanted structural changes in the ship, and that the team will need to monitor the vessel for damage along the way.

And as for how much the project will cost?

“I have no idea,” says Olofsson. “This is a collaboration between the Vasa museum and Sandvik. It’s a research project from both parts. There’s no real money involved with this. Sandvik handled the material, the stainless steel. And we do some work and have ongoing tests for a long time ahead.”

CENTURIES OF AMBITION

Because they're partly hollow, the new bolts weigh less than the old ones, by a combined weight of about 7 tons. That will help reduce the weight of the ship overall.

“The ship is moving downwards, slowly, slowly, and we want to get rid of as much weight as possible from the hull,” says Olofsson.

Doomed from day one, the royal ship first suffered from the overly ambitious King, who loaded it with more cannon than it could bear and still sail. The top-heavy ship sank, and some 150 people drowned on the way down. Salvaging the 67-meter long vessel from the sea was also an ambitious task, and so was the subsequent building of a whole museum around the ship. For the last 50 odd years, the ambition has lain with the preservationists. How long can they keep the ship afloat in the current of time?

Olofsson says that the Vasa is the only complete ship in the world that is preserved from the 17th century, and he hopes the ship will survive for 1,000 years.

“I’m sure I can keep that promise,” Olofsson chuckles.

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