The famous warship, Vasa, displayed in a museum that gets 1.2 million visitors every year and ranks as one of Sweden's most popular tourist attractions, is deteriorating despite ongoing preservation efforts, scientists are reporting. Their study, citing a "significant" loss of strength in the ship's wood, appears in ACS' journal Biomacromolecules.
Ingela Bjurhager, Lars A. Berglund and colleagues explain that the Vasa sunk in the Stockholm harbor in 1628 on its maiden voyage after sailing less than a nautical mile. The ship was rediscovered in 1958, raised in 1961, treated with preservatives and finally put on display in the Vasa museum in 1990. The museum preserved the ship with polyethylene glycol (PEG) in a thick, wax-like preparation dissolved in water and sprayed onto the wood for 17 years. Concerns about deterioration arose, and the authors set out to determine the effects of PEG, iron from nails and rivets, and sulfur from decaying bacteria on the wood's strength.
The team analyzed the strength of wood taken from various locations in the ship's hull, which is largely made of oak. They report that at its worst, the wood had weakened as much as 80 percent. They suggest the loss of strength may be a result of letting the ship dry out after its recovery, allowing oxygen to react with the iron in the wood. Although they don't foresee an immediate danger to the ship, a clear understanding of the cause of the wood's degradation will be critical to preserving it for future generations. In parallel, an improved support structure is needed to minimize the stresses and deformations in the wooden hull.