In a race against time

The successful reconstruction of a shipwreck from 1188: archaeologists have announced their research results on the discovery of a medieval shipwreck four years ago in Wismar harbor. According to the findings, the ship is much older than assumed at more than 800 years old

It was the third sensational discovery made by underwater archaeologists during the expansion of the seaport of Wismar in Mecklenburg-Western Pomerania. After two shipwrecks over 700 years old were discovered in April 2016, the experts came across a third large ship at the end of 2017. It was resting at the bottom of Wismar Bay three meters below the water surface: a robust cargo ship 24 meters long and four meters wide, almost completely preserved thanks to the anaerobic conditions in slightly acidic water, protected from bacteria, rot and woodworms. Careful documentation of the wreck revealed that the ship was a descendant of the Viking ships.

Marine archaeologist and salvage manager Dr. Jens Auer (Mecklenburg-Vorpommern State Office for Culture and Monument Preservation) describes the “great ship of Wismar” as medieval shipbuilding at its finest: “This heavy cargo ship of Nordic construction style was built with great care and was immensely durable. It was built with overlapping pine planks in clinker construction and has beautiful curves. As it was in use during a rather peaceful time, it probably carried cargo such as wood, STEIN or heavy loads of beer.” Oak and pine trees were necessary for the construction of the large cargo ship. They were probably felled in western Sweden between 1184 and 1190.

But just a few years later, the sturdy merchant ship made its last voyage to the southern Baltic coast and sank in the Bay of Wismar. The wreck is the “best-preserved and most complete find of a ship type to date”, explains Auer. “It marks the transitional phase from Viking building traditions to Nordic clinker shipbuilding in the Middle Ages.” According to Auer, the construction and use phase of the merchant ship thus falls into a period in which Danish maritime trade flourished under the rule of Knut VI and Valdemar II.

It is hardly surprising that the wreck was found on the southern Baltic coast, as this was part of the Danish dominion at the time. “What is interesting, however, are the conclusions that can be drawn for the history of the town of Wismar. Obviously, the “portus Wissemer” mentioned in 1209 was already an important enough port for a large Scandinavian merchant ship to call at before the town was founded,” continues Auer.

But what should be done to preserve this treasure? Even the salvage was a race against time, as the onset of winter was imminent. And how could the 228 individual parts of the sailing ship be mapped quickly enough after salvage to protect the now oxygen- and drought-exposed goods from decay? Using a conventional 3D scanning method such as the FaroArm tactile 3D scanner, it would have taken over a year to document the intricacies of the construction and the state of preservation. Expert Auer knew that they had to get there faster.

He put together a team with the best available specialists in underwater archaeology, photogrammetry and 3D imaging: Thomas Van Damme, Massimiliano Ditta, Marie Couwenberg and Benjamin Halkier. During a previous job in shipwreck conservation, Auer had already become acquainted with the Artec Eva 3D scanner: a lightweight handheld 3D color scanner based on structured light technology that allows non-contact scanning. When Auer tested the scanner on wet ship planks and saw how quickly and accurately the scanner captured the full spectrum of the wood structure, his decision was made immediately. They would use the Artec Eva grazing light scanner.

And the success proved him right: “Seven planks a day, including cleaning, scanning, annotation, description and photography. Our team of four documented all 228 wooden components in 33 days,” explains Massimiliano Ditta. And Van Damme adds: “Artec Eva has the great advantage that it is much more user-friendly than photogrammetry. Even people who have little experience with 3D scanning could have done this documentation. It was really fun to scan the wood with this device because it is very easy to handle. Previously, we would have had to take over 300 close-ups of each piece from the most varied and uncomfortable angles.”

The result is impressive. After the planks were scanned from all four sides and then converted into colored polygon meshes, there are now perfect digital replicas of the planks. In addition, all the features of the wooden planks were fully captured. Using the Rhino 5 3D modeling application, the details were saved on the exact layers where they are located on the wood. Van Damme explains: “The annotations included details of every cut and every axe blow, all the nail holes, the smallest scratches and the wood grain. It was noted which tools were used in each case and which nails were used, whether iron or wooden nails. We also checked whether there was any evidence of repairs and which part of the tree a piece of wood came from.”

Read more in RESTAURO 2/2020.