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The Swan—A 17th Century Story at the Bottom of the Baltic Sea

The Finnish dive team Badewanne has helped complete the documentary “Fluit,” about the 17th century Dutch fluyt shipwreck, The Swan, they discovered at a depth of 85 m/279 ft in the Baltic Sea in 2020. Explorer/instructor Edd Stockdale recounts the tale.



by Edd Stockdale

Header image: Photogrammetric 3D model of the wreck shown from starboard-bow side (ortho-metric projection). Photos by Badewanne Team, copyright Handle Productions 2021. Drawing by Niklas Eriksson copyright Handle Productions 2021

There are very few places where the preservation of shipwrecks is as good as in Baltic Sea. Due to low oxygen, cold water, low light, and absence of wood-boring organisms, the condition of ships that have sunk in these waters is extraordinary and, combined with the importance of the Baltic Sea for maritime trade, and as a site of historical conflicts, has resulted in large numbers of underwater time capsules in the form of well preserved wrecks.

The Badewanne team of volunteer divers based in Finland has for the last 20 years made it their mission to explore and document these historical shipwrecks and bring video evidence to the surface in order to share it with the general public.

  Through close collaboration with researchers, heritage organisations, and governmental departments around the world, the team has found, identified, and documented many wrecks lost from the 17th century to WWII.

Reconstruction drawing showing the ship with the transom in place at stern. The transom found at the seabed probably has a rusted attachment point where the lantern has been. It’s shown in the drawing. Drawing by Niklas Eriksson

One such wreck was discovered in July 2020, when the team descended to 85 m/279 ft onto what they thought was a WWI minesweeper. To their great surprise and excitement, they instead discovered a 17th century vessel of Dutch fluyt built sitting upright on the bottom in an almost-intact condition aside from some trawl damage.

The fluyt design, a three-masted ship, with a very large cargo capacity for its r size, and an innovative technical design which allowed a smaller crew to man it, were highly successful vessels that increased the profitability of their voyages. Due to these features, their success hugely expanded Dutch trade throughout the world, including the Baltic Sea trading for wood, tar and hemp, as part of the merchant navy. 

Swan has been carved onto the transom. It was name of the ship

The original discovery in 2020 was well received by world-wide media, and the story was shared through many media channels, including Quest V 21 No.3, Project Baseline in Finland Raises Awareness of Threats to the Baltic.” Collaborative links to continue research of the wreck were also made with maritime archaeologists Minna Koivikko from the Finnish Heritage Agency and Martijn Manders from the Cultural Heritage Agency of the Netherlands, along with fluyt expert and maritime archaeologist Niklas Eriksson from Stockholm University. 

In 2021, the team returned to continue research on the vessel and filming for the historical documentary film “Fluit” (alternate spelling), produced by Handle Productions, following the investigation of the origin and the mission of the fluyt, the identity of her sailors, and her untimely fate in the 17th century Baltic Sea. 

Members of the Badewanne Team from 2021 Swan identification, from the left: Mauro Sacchi, Edd Stockdale, Tiffany Norberg, Ivar Treffner, Jouni Polkko, Sam Stäuber, Tommi Toivonen, Jani Tattari, and Roope Flinkman

As the team recorded photogrammetry footage to produce a detailed model in 2020, specific tasks were already established for the 2021 return. These included making exact measurements of specific sections of the wreck to get an accurate 3D model, searching for specific sections of the wreck, and investigating the debris field around the actual hull.

Located in this field was a specific artefact of interest, which was previously thought to be the ‘Hoekeman’ feature, a carving of strong men aimed to display the success of the merchant but, with more detailed survey, it was identified as the transom plate of the vessel, face down. This was highly exciting, as these often displayed the date of manufacture and a pictographic form of the ship’s name and as such was highly valuable for expanded  insight into the history of the vessel.

After consultation with the archaeology team and careful planning of how to proceed, the transom plate was turned over to reveal both the date and a carving of a swan to the huge excitement of the team.

“The identities of ships were revealed by the carved motifs on the transom. Fragments of such motifs have been found before, but now that we have the entire composition, we are able to identify the ship in the same way as people in the 17th century did. The ship was named “Swan” and built in 1636. A closer examination of the transom will most likely reveal the coat of arms for the ship’s home port, as well,” celebrates maritime archaeologist Niklas Eriksson. 

Wreck of a Dutch type fluit ship, possibly from 17th century or early 18th century. First dived by the Badewanne team in July 2020

After documenting the transom plate both for video and 3D photogrammetry modelling, we began the next stage of research into this rare remaining example of what was once a hugely common ship and insight its history:

“These new findings are a great starting point to do more research. Knowing the launch year of the ship, 1636, and having an indication of the name of the ship helps us to learn more about the historical context. We may even be able to identify the people on board. The new findings also help us to learn more about the fluyt: a simple, common ship that created the right circumstances for early globalization. The fluyt highlighted the typical Dutch approach to ship building, and symbolized the flourishing seafaring trade of the time,” states maritime archaeologist Martijn Manders. 

 Jouni Polkko, one of the founding members of Badewanne and a leader of the team, sums it up well, “It was incredible to be the first people to see the wreck since it sank nearly 400 years ago, and now we have the opportunity to take her story up to the surface.”  Twenty years of discovering and documenting un-dived wrecks in the Baltic gives an insight into the level of excitement that this work has produced as well as the opportunity to share it with the public with the Handle Production documentary. 

”Fluit” is a documentary film project by Handle Productions. The film is directed by Sakari Suuronen, written by Beata Harju, and produced by Hanna Hemilä. Co-producer is Annemiek van der Hell from Windmill film, Netherlands. The diving project has been financed by i.a. the Foundation of Antero and Merja Parma and Swedish Television. 

Badewanne consists of volunteer divers from different nationalities. The team specializes in documenting wrecks in the Gulf of Finland. Badewanne is also involved in research of environmental threats of shipwrecks. The divers participating in the research of the fluyt have been Jouni Polkko, Tommi Toivonen, Sam Stäuber, Jani Tattari, Ivar Treffner, Mauro Sacchi, Tiffany Norberg, Edd Stockdale, Harri Laakso and Juha Flinkman. 

Edd Stockdale has worked in scientific and technical diving for over a decade and joined as Badewanne team member in 2019. He is the coordinator of the newly established Finnish Scientific Diving Academy at the University of Helsinki which was established to develop scientific diving training to further research abilities and develop new approaches to data collection in cold water based science.  When not working on research diving, Edd can be found exploring the mines and wrecks in the Nordic region or planning the next adventure. He is supported by Divesoft as well as Santi, Halcyon, and REEL Diving in Scandinavia. 






Text by Andrea Marassich. Photos courtesy of Phreatic. Header image: An inflatable (aka The love boat) is used to facilitate transportation of diving gear through the lakes.

Locoli cave is an amazing and challenging spring in the wilderness of Montalbo, Sardinia. It took me three years to set up the project, but it was all worth it. After all, David Rhea taught me that, “Slow is smooth, smooth is fast.”

I’m Andrea Marassich. I began exploring underwater caves in 2003, and I have taken part in cave exploration missions all around the world. In 2010, I fell in love with the powerful, majestic cave systems of Northern Sardinia, Italy. As a result, in 2014, I founded a nonprofit association, Phreatic, which collaborates with scientists and researchers in geology, paleontology, and earth sciences to study and document these unique environments. 

In 2019, I presented at Icnussa, the international speleology meeting in Sardinia, and spoke about Phreatic projects. During the event, a local caving club offered to carry diving gear to the first sump of a cave I had never heard of: Sa Conca ‘e Locoli. I dove with fellow GUE instructor Stefano Gualtieri, and  it was love at first sight. During the dive, I realized that I wanted to get back for more survey and exploration.

The Environment

“Locoli” is a temporary spring (active after rainfall and during certain seasons) located into Montalbo limestone massif, and is included in the UNESCO MaB (Man and the Biosphere) reserve of Tepilora, Rio Posada e Montalbo. 

Unesco Mab Tepilora Park: Karst, wetlands and coastline.

This Sardinian version of the Dolomites Alps, with its white rocks, looks out onto 25 km/16 miles of coastline. The silver ridge of Montalbo features evocative itineraries: historic trails for coal merchants and shepherds, archaeological sites, holm oak forests, and Mediterranean scrub (populated with mouflon, the golden eagle, and the red-billed chough). The peak presents doline valleys, chasms, underground rivers, as well as caves prehistorically inhabited by the Nuragic civilization. Archaeologists uncovered iron weapons in Bona Fraule, Gane ‘e Gortoe is rich in limestone concretions, Sa Conca ‘e Locoli  is eroded by the fierceness of the water, and Sa Prejone ‘e ‘Orcu is a cave-sanctuary.

Sa Conca’e Locoli

Locoli spring, which can submerge the whole valley during winter flooding, forms the entrance to the massive cave system hidden beneath Montalbo. The entrance cavern leads to a series of crystal-clear, freshwater lakes, and though the access is not technically complex, it requires the use of ropes through multiple changes of elevation, while the decorations and speleothems inside alternate with the smooth rocks levigated by water passage. 

Rope work and SRT is required to reach sump1. Hauling gear and physical effort is a serious part of the game.

After the lakes, the cave splits in two. The south passage leads to a shallow sump looping back downstream and connecting to a minor spring in the valley. The north passage goes through a series of changes in elevation, which require the use of ropes, and leads to a wide passage that provides access to the surface of Sump 1. 

This is the entrance gate to a series of huge flooded passages of breathtaking dimensions with obvious signs of a huge aquifer. The first sump is not particularly long or deep at 250 m/820 ft long with a maximum depth of 23 m/76 ft, but it leads to a very important second split. Here the subterranean river flows downstream toward the village of Siniscola and the Fruncu ‘e Oche spring, while on the upstream side it heads toward four other challenging sumps and dry areas. 

In the island of Sardinia, Sump 3 is the deepest, reaching 90 m/295 ft. 

The last exploration dive carried out in 2009 by Rick Stanton led to a collapse in Sump 5; consequently, the present survey only covers the first two sumps.  

The Project

In 2020, I organized the first scouting mission of the deeper sumps, together with Jan Medenwaldt. COVID-19 travel limitations presented difficulties in gathering a bigger team. 

In 2021, finally, we managed to organize a three-week campaign encompassing both survey and photogrammetry. The exploration of the system is particularly complex for a variety of reasons. First, the underwater portion is accessible after a relatively long dry passage, one in which cavers and cave divers must carry all their heavy gear. Subsequently, the series of sumps is difficult from a technical point of view, as the diving profiles involve serious exposures in Sump 3 and 5. 

After the dives were completed, the long clean up requires a couple days, but the smile don’t lie. Operations went smooth.

In order to complete the working goals connected with survey, mapping, photo/video, and research tasks, divers needed to extend their diving time and elected to stay inside the cave and set up a bivouac; entering the cave with dry tubes and bivouac gear without knowing where to establish the camp was risky. We found a new dry section between Sump 3 and 4, which proved to be ideal to bivouac and minimize the decompression risks connected with the profile. 

The main challenge is dealing with the geology of the cave, one that presents multiple elevation changes to move from one sump to the next. Sump 3 is the most demanding of the five underwater galleries, as the cave drops initially to 45 m/148 ft deep, then rises to 15 m/49 ft, drops to 90 m/295 ft, ascends again to 45 m/148 ft, and drops again to 65 m/213 ft before the final ascent. 

We deeply believe exploration without documentation is not getting the job done. Survey and documenting with media is a key component of our activities and we prioritize it over simply “reaching a distance”.

The exploration efforts are now divided in two areas: the newly discovered dry section between Sump 3 and Sump 4, featuring massive rooms and high chimneys that potentially connect with a fossil gallery above, and Sump 5, whose exploration stopped at a depth of 50 m/164 ft and needs  further investigation.

We are already working on new project sessions for summer 2022. 

Considering the importance of the karst system of Montalbo and its water reservoirs, the UNESCO MaB reserve decided to support our project, specifically in relation to our documentation and conservation efforts. We also received the sponsorship of the Italian Speleological Society and are now searching for more partners. 

The main objectives will be:

  • Completing the survey of the upstream section up to Sump 5. To perform this task, we will use the SUEX DRIVe and mapping devices combined with MNemo.
  • Creating a documentary featuring the most beautiful passages of the cave with the help of an expert photogrammeter and videographer.
  • Improving public awareness about caves and karst in partnership with the International Year of Karst and Cave initiative provided by the International Union of Speleology.

Citizen Science

Phreatic believes in the power of Citizen Science. All our projects and missions rely upon the crucial involvement of skilled, specially trained individuals. The Sa Conca ‘e Locoli cave project involves a number of local and foreign volunteers with various sets of competences. Many thanks to Speleo Club Nuorese for the support in the dry portions of the cave, and to all the Phreatic volunteers who joined us in 2021 including Jan Medenwaldt, Peter Brandt, Sven Bertelmann, Keith Kreitner, Laura Marroni, Elke Riedl, and Irene Homberger. 

Entrance of one of the multiple downstream passages; While one team was diving the upstream sumps and bivouacked in the further section, operations continued with oc team working in a different area.

Collaborations and Partnerships

Phreatic can count on a long-term partnership with SUEX, a world leader in high-performance underwater vehicles designed for long-range technical and professional diving.

The Locoli project operates under the supervision of the geologist Dr. Francesco Murgia, author of multiple scientific publications on the areas of Montalbo and Supramonte.

For more information see: Phreatic: Citizen Science and Groundwater Research. Email contact:

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