Shipwreck expedition to the Baltic Sea

Anne Marie Høier Eriksen & David John Gregory
National Museum of Denmark

During reconnaissance the early 2000s and prior to the installation of the North Stream pipelines, three wrecks were picked up by sonar, but the reconnaissance team could not stop for a closer examination of the wrecks at the time of discovery. A group of experts and sailors some twenty-seven people strong were quickly assembled at the end of October 2022 before shipping out of Västervik in eastern Sweden bound for the Gotland Deep.

We had one week to prepare for this expedition to the Baltic Sea. An extraordinary and rare opportunity had arisen as the M/V Sima had been surveying in the Gotland Deep and was kindly made accessible for a research expedition by Gert Norman, the owner of J.D. contractors and founder of the Sea War Museum Jutland, Denmark. In terms of research, the advantages of participating were phenomenal, especially as the costs for running a vessel of Sima’s size are normally prohibitive for archaeological projects and we wanted to make the best use of the time as possible.

The day after departure from Västervik we arrived at the first of the three positions marked the pipeline reconnaissance team. The wreck site was quickly relocated with the ships multi-beam-echosounder. The ROV (Remotely Operated Vehicle, an unmanned underwater robot) connected to the ship via cables was prepared and sent down to the wreck for a closer look. See Figure 49.

Figure 49. The ROV (equipped with cameras and lights) was prepared to be sent 150 meters down to the wreck. Photo by Anne Marie Høier Eriksen.

The ROV’s full complement of advanced cameras relayed data up to the control room located in a container where a pilot navigated the ROV using a large number of screens and controls. See Figure 50. Understandably, the pilot was not alone in the room—it was full to bursting with the other expedition participants. The atmosphere was thick with anticipation as the ROV navigated through the complete darkness more than 150 meters below the ship.

Figure 50. The experienced ROV pilot from Ocean Discovery is navigating the ROV over and around the wreck while taking photos. Photo by Anne Marie Høier Eriksen.

Perfect preservation

The surprise and delight felt by the crowd was audible as the proud outline of an extremely well-preserved ship first caught the light from the ROV. The visibility was about 4-6 meters, which enabled a good view of the wreck as the ROV moved slowly over and around the wreck. The two masts remained standing, although the sails, rope and metals have decayed. See Figure 51. On the deck we sighted a broken dinghy, a tragic reminder of the events that preceded the wrecking of the vessel. Another gasp gusted through the control room as the ROV camera captured a figure of a man’s head carved in wood located at the top of the steering rudder. See Figure 52. In terms of style, this figure allows us to date the ship to around the 16th-17th century. In addition to the ship’s lines, this head is an indication of Dutch shipbuilding techniques, suggesting that the vessel had originated in the Netherlands.

Figure 51. Wreck 1 – A photogrammetric model of the 27 meter long excellently preserved shipwreck dated to around the 1600s. Model by: Ocean discovery, Sea War Museum Jutland

Figure 52. Wreck 1 – on the steering rudder a carved wooden figure of a man’s head with a bird on top (possibly a swan) was located. Model by: Ocean discovery, Sea War Museum Jutland

The thousands of photos taken by the cameras on the ROV were stitched together as a mosaic creating a 3D photogrammetric model of the ship. See Figure 51. Raising and conserving the ship would be extremely difficult and costly (Björdal and Gregory 2012; Rule 1982; Hocker et al 2012); by using this technique, we can still get a good overview of the wreck which can provide detailed information about shipbuilding techniques and the maritime trade and seafaring in the Baltic Sea.

Besides the models we also obtain data of the extreme environment in which the wreck is located. A datalogger measuring the conductivity (used to calculate the salinity), temperature and depth was also sent down to the wreck site on a winch from the deck of Sima. Among other things, such parameters can give us a good indication of why the ship has remained so well preserved.

Termites of the ocean

A wooden ship wrecked in waters with higher salinity and oxygen levels than those surrounding this wreck would quickly be colonised and degraded by Teredo navalis, a boring mussel also known as shipworm. New wood with a high amount of cellulose can completely deteriorate over a few months. However, the shipworm not only needs wood for protection and nutrition, but it also needs to filter the ocean water for oxygen. The low oxygen content of the waters here are the main reason this wreck is so well preserved. However, in terms of overall preservation at the site, the microbial deterioration of the wood and other organic materials as well as the corrosion of metals will still be a problem in the long run. Thankfully, this kind of degradation takes hundreds (or even thousands!) of years. The depth at which the wreck is found is not only favourable for preservation in terms of low oxygen level; it also reduces of other environmental risk factors, such as sea currents and erosion as well as additional hazards from fishing and other human impact.

Figure 53. A sample was brought back to the surface for dating and further analysis at the laboratory by the National Museum of Denmark. The sample was a naturally broken piece of the wreck which was laying away from the wreck, so it could be collected without disturbing the site.

Back in the lab

Although a lot of information can be gained from the photogrammetric model and the measurements obtained from the dataloggers, it can be possible to learn about the origin of a wreck by examining the wood from which it was constructed. However, as we did not want to disturb the wreck site in order to secure a sample of the wood we searched until we found a suitable piece broken off from the wreck and slighted removed from the main area of the site which we could bring back to the lab for further analysis.

We are currently working on analysing the material. Please follow the research of this (and other) analyses done by the ENDURE project here.


  • Hocker, E; Almkvist, G; Sahlstedt, M (2012) The Vasa experience with polyethylene glycol: A conservator’s perspective. Journal of Cultural Heritage, 13:3, p S175-S182
  • Rule, Margaret (1982) The Mary Rose: the excavation and raising of Henry VIII’s flagship. London: Conway Maritime, p 224
  • Björdal, C. G. & Gregory, D. 2012. WreckProtect: Decay and Protection of Archaeological Wooden Shipwrecks, Oxford, ArchaeoPress.

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