Halfway through and a whole elephant lighter
June 2016 brought the halfway mark in the bolt exchange that will help save the national treasure and world attraction Vasa — a royal warship that sank to the bottom of Stockholm’s harbor on its maiden voyage in 1628. Detailed evaluations of the renovation work so far show exciting results. Thanks to pioneering materials and design in the bolts, Vasa is now more stable and significantly lighter. A whole, full-grown elephant lighter, actually, with weight savings of five tons.
Partnering to save a royal warship
Back in 2011, the Vasa Museum and Sandvik Materials Technology began a long-term research and development partnership to save Vasa from the corrosive damage its existing bolts were causing in the aging timber hull. So far, the team has replaced roughly half of the more than 5,000 bolts using a combination of SAF 2707 HD™ and SAF 2507®, materials normally used in the most demanding environments in the oil and gas industry.
Exhaustive evaluations show exciting results
During 2013, thorough evaluations measured movements and pressure and their effects on the ship. The new bolts were measured and logged around the clock with sophisticated equipment with an accuracy of a hundredth of a millimeter. A full year of measurements showed that the new bolts exceeded expectations.
“The environment inside Vasa’s timeworn oak is chemically complex. Now we have confirmation that the calculations and tests carried out before the bolt replacement, as well as the methods used for the insertion, were correct,” says Anders Ahlgren, engineer for the Vasa Museum. “We see that the bolts behave extremely well and, by far, meet our expectations. Thanks to the design of the bolts, we have more control and can see immediately if the hull moves,” he continues.
The successful exchange of roughly half of the 5,000 bolts on Vasa was celebrated with a ceremony at the Vasa Museum. Petra Einarsson, President of Sandvik Materials Technology, received a symbolic elephant plaque during the event in honor of the significantly lighter load Vasa will bear into the future.
Now, work with the bolt replacement is intensifying. Additional people have been hired to help replace the remaining rusty bolts with Sandvik's new high-alloy bolts. The ambition is to have all of the bolts replaced in 2017.
“Sandvik has been an invaluable support, and we feel confident in the materials and the design. We expect these bolts to remain in place for at least 150 years,” says Anders Ahlgren, engineer at Vasa Museum.
Footnote: a full-grown African elephant weighs about five tons. The heaviest elephant ever on record weighed 12 tons.