New deterioration scare for Sweden's Vasa
13 Sep 2012, 17:57
Published: 13 Sep 2012 17:57 GMT+02:00
"Our research shows that the strength [of the wood] has fallen dramatically. We didn't know this previously," Lars Berglund, a professor at the Wallenberg Wood Science Centre at Stockholm's Royal Institute of Technology (KTH) said in a statement.
The findings of Berglund and his team come after analyzing the effects of the polyethylene glycol (PEG) which was sprayed on the ship after it was lifted out of Stockholm's harbour in 1961, in combination with the effects of iron from nails and rivets as well as sulfur from decaying bacteria.
The researchers concluded the Vasa's wooden hull had been weakened by as much as 80 percent, suggesting that the loss of strength could have been a result of letting the ship dry out after it was recovered, prompting a reaction between oxygen and the iron in the wood.
On average, the wood of the Vasa only has about half of its original strength, the researchers found.
"This is also the first time that someone has shown that the breakdown has practical consequences. In other words, if you take an oak plank and put weight on it, it won't tolerate as much as it would have before," said Berglund.
The challenge now is to better understand exactly how Vasa's wooden structure is deteriorating and what to do about it.
"The first step now is the figure out how fast the breakdown process is and do a qualified risk assessment," Berglund told the TT news agency.
The Vasa was commissioned by Swedish King Gustav II Adolf in 1625 and was designed to be the mightiest warship in the world.
It was armed with 64 guns on two gun decks, but did not have enough ballast to counteract the weight and sank just minutes after setting sail on its maiden voyage.
A Swedish shipwreck enthusiast, Anders Franzen, located it in 1956 at a depth of 32 meters.
The ship was raised in 1961, and the museum built around the ship opened in 1990. It is one of the most popular tourist sites in Scandinavia, with 1.1 million visitors annually.