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The discovery and Lifting

A huge wooden wreck emerged on October 9th, 1962 during dredging for a new dock in Bremen. Never had the captain of the dredger seen a more peculiar ship. The country’s archaeologist and historian of the Bremer Landesmuseum, Siegfried Fliedner, identified it as a Cog.
Lifting the ship as a whole was not possible. On touching the iron nails or wooden dowels, they fell off the hull. The ships timbers did not hold together any more.
Fliedner had all planks and beams, which were accessible at low tide, measured and given numbers, a helmet diver then extracted them one by one. In the turbid water the diver could only feel his way. Heavy parts were lifted onto a pontoon by a floating crane.

Picture: Archive DSM

The reconstruction and the conservation in the DSM

The reconstruction of the Bremen Cog in the German Maritime Museum took seven years. For a beginning shipwright Werner Lahn and his men laid out the parts of the puzzle in the cog-hall of the museum. A river barge had brought the 45 tonnes of cog timbers, or 2000 pieces, down the Weser to the German Maritime Museum in Bremerhaven. Several lawn sprinklers kept the timbers wet to prevent them from drying and shrinking. Nozzles along the ceiling filled the hall with fog. The large waterlogged timbers were very heavy. Only with a mobile and easily manoeuvrable crane could the shipwrights handle them and fit them into the growing Cog. Working from ladders and scaffolds was difficult. The men suffered from heavy colds and rheumatism, as the humidity in the hall was about 97 %.Some plank fragments only found their right place in the hull after long inspection and repeated trials.

The Bremen Cog was an extraordinary large archaeological find of waterlogged wood. Ever since archaeologists excavate wooden objects of the past from bogs, lakes, and rivers, they had to learn that in open air the wet wood shrinks, warps, and cracks; even if it is well preserved and does not show any degradation.
Steel workers push the bottom plates for the conservation tank under the Cog.
For the Cog we have developed a novel conservation method. It consists of two treatments: first the Cog was submerged in a bath with PEG 200, and then in a bath with PEG 3000. The tank in figures: 800,000 litres capacity; 110 tonnes of steel, thereof 37 tonnes inoxidable; 11.5 cm thick glass windows to allow museums visitors to see the Cog during conservation. In the winter 1995/1996 13 tank lorries brought each of them 20 tonnes of 100 °C hot molten PEG 3000 from the producer in far off Bavaria to the Deutsches Schiffahrtsmuseum on the mouth of the Weser. In the museum we added water: For the second bath the solution had to be 60 %.In 1999, the conservation has come to its end – after 19 years.
Steel workers from Motorenwerke Bremerhaven cut the conservation tank to manageable pieces. No steel items nor any molten steel droplets from the plasma-torches were allowed to fall onto the precious wood. We used spatulae and knives, steam jets and hot air blowers to remove excess PEG. We fitted new steel rods into the support system. The Bremen Cog is an exceptionally large and nearly completely preserved ship from medieval times. She is 23.27 m long, 7.62 m wide, and 7.02 m high to the top of the capstan on the castle deck. She holds 160 m³.

Picture: Hans-Jürgen Darlison

Picture: Archive DSM