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The
Vasa
On
her maiden voyage into the Stockholm archipelago on August
10, 1628, the Swedish warship Vasa was broadsided by
a sudden gust of wind while still in sight of the shore. Despite the misgivings of the ship's
designer, she had been built with an extra deck, added late in the constuction process at the order of King Gustavus Adolphus. The additional mass made her top-heavy, and especially susceptible to rolling. Off-balance and unable to resist the gust, she heeled to port, seawater flowing into the open
cannon ports in her side. Within minutes, the magnificent
warship was sitting under 30 meters of water, a victim of
royal hubris. About 50 of her 150 crewmembers died in the
disaster. Attempts to raise the vessel soon after the wreck
succeeded only in righting her on the bottom and allowing
the recovery of many of her cannons.
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The
remains of the Vasa are brought to the surface of Stockholm Harbor in 1961.
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Incredibly,
the location of the ship was forgotten until 1956, when a
search by amateur archaeologist Anders Franzen ended in the
retrieval of a core sample of black oak from her hull. The
brackish water, lack of oxygen, and scarcity of wood-eating
shipworms in the Baltic Sea had left the Vasa remarkably
well preserved. She was in such good shape, in fact, that
a committee formed by the Swedish Navy and the private company
Neptunbolaget decided to raise her in one piece.
Divers dug six tunnels in the mud beneath the Vasa
and threaded cables under her, a laborious and dangerous task
that took almost a year. With the cables attached to pontoons,
the vessel was lifted gradually from the bottom, beginning
a nine-month trip to the surface. To help stabilize the hull,
some 5000 oak pegs were driven where the iron nails had long
since corroded away. Although the hull was not watertight,
underwater pumps removed water faster than it was coming in,
and the ship's natural buoyancy took over for the cable lifting
system. After being on the bottom of the harbor for 333 years,
in 1961 the upper decks met fresh air, and the Vasa
floated once again.
Raising
the Vasa was only half the battle, however. Like the
Hunley, the years underwater had left the ship in a chemically
fragile state, subject to rapid decomposition in the open
air. In addition, the water-impregnated timbers were in danger
of shrinking to one-fourth of their volume as they dried out.
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Efforts
to preserve the Vasa
continue in her new
home, the Vasa museum.
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Archeologists
immediately began working to preserve the ship. Polyethylene glycol (PEG), a compound which had been used to preserve
smaller Viking ships, was to displace the water in the
oak timbers of the Vasa. No object of such great size had ever been stabilized in this
way, however, and special methods had to be developed to apply
the PEG. Between 1962 and 1965, the ship was sprayed
down manually once a day with the preservative, a process
that took 25 man-hours to complete each time. Eventually,
an automated system was developed to take over this task.
Humidity and temperature are carefully maintained
around the vessel at her current home in the Vasa Museum
to prevent shrinking and swelling of the centuries-old timber.
Condensation must be guarded against, as moisture on the surface
of the wood could leach out the PEG preservative, and lighting
is kept low to halt photo-degradation. Despite these precautions,
the Vasa faces a new threat in the form of sulfuric acid,
created when sulfur trapped in the ship's timbers during her
many years on the ocean bottom combines with oxygen in the
air. The acid attacks and breaks down wood, and chemists at
Stockholm University are currently working on a solution to
this serious problem. Constant vigilance will be required
to preserve the Vasa for future generations.
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