Excavation, recovery and conservation of a 15th century Cog from the river IJssel near Kampen in the Netherlands

On the 15th of September 2015 the excavation started of at least three medieval shipwrecks. The largest of these, an early 15th century cog, was first discovered in 2012. The discovery of all three shipwrecks was made during an archaeological survey carried out in preparation of a large scale dredging project in the IJssel river. This project is part of a Dutch national programme building flood defences along all major rivers.

Last week the diving platform and a pontoon with heavy lifting equipment have been positioned above the findspot in the middle of the river. After completing further survey and coring work on the site, the underwater excavation and documentation of the wrecks and other related objects will take place over the next three months. The ultimate goal is to excavate and raise the cog in as intact a state as possible before the end of this year. After lifting, the cog and all other recovered wrecks and objects will be transported over water to Lelystad on the IJsselmeer coast, where a purpose built conservation facility is being prepared at the premises of Batavialand Foundation. The whole process of post-excavation, research and conservation, will take at least three more years. If all goes to plan, the stable cog will be returned to Kampen and displayed at a special exhibition near the site of its original discovery, and next to the well-known replica the Kamperkogge.

Excavation under water
The bodies of the three wrecks are for the most part sunk into the river bed and covered by layers of river sediment. First a detailed inspection and documentation of the area around the wrecks will take place. After that marine archaeologists will remove the sediment around the wrecks, using airlifts. Archaeological divers will work behind a wide purpose-built and movable screen. The screen is intended to protect not only them but also the uncovered archaeological remains against the natural currents in the river. Even behind the screen visibility will be poor, normally less than 1 meter, further complicating the work.
Before lifting, all objects and finds will be documented in-situ using high density multibeam techniques. On-board and underwater cameras will record the whole process, and on-site archaeologists will produce instant site plans and 3D-reconstructions based on actual data. The smaller wrecks, probably two river barges, will be raised first and assessed by specialists working on site.

Raising the Cog
The cog, named the IJsselkogge in the media, is the largest of the three wrecks, measuring 20 meters in length and 8 meters wide. It seems to have been preserved in the river bed from the keel up to the height of the deck(s). The ship is listing at an angle of circa 20 degrees and it’s position is at a right angle to the course of the river, its prow pointing towards the riverbank on the Kampen side.

The preferred scenario is to raise the wreck by means of a unique, purpose-built cradle. A steel construction of beams, supports and braces will be placed over the wreck. From this construction 20 slings will be passed under the wreck using an ingenious water injection system, The slings will be interspaced at a distance of circa 1 meter along the hull of the cog. The pull on each individual sling will be electronically monitored and can be adjusted when necessary. After positioning the slings, the cog will be gradually excavated inside and out. while at the same time slowly pulling-in the slings and placing extra supports where needed. Hanging in its slings the cog will initially be turned upright and then slowly hoisted. A computer programme constantly checks the pressure of each sling on the hull during the operation. After surfacing, the whole construction of cog, cradle and screen will be placed on a pontoon.

It is expected that the archaeological work under water will take until the middle of October to complete, including the recovery of the smaller objects. The actual lifting of the cog is planned for early December 2015. The conservation work in Lelystad will begin early 2016.

A ship graveyard?
Archaeologists and historians are trying to find an explanation for the wrecks on this site. So far neither inventory nor cargo has been found in or near the wrecks. An accidental sinking or other maritime disaster therefore seems unlikely. One hypothesis is that all three wrecks were deliberately sunk at this location in order to block off a former side branch of the IJssel river. By blocking the side branch, more water would have been forced through the main river channel, eroding the underlying river bottom and thus stopping or delaying the silting-up process. Many historical written sources refer to problems for ships reaching Kampen in the first half of the 15th century because of the shallowness of the river. Sources also refer to measures taken by the town council to improve navigability. It seems a remarkable coincidence that the remains of a medieval water management project have been discovered as part of a modern day water management project.

Why raise the cog?
Dredging is necessary to enlarge the water discharge capacity of the Ijssel river. Over the next couple of years dredging will take place in the river over a length of 7,5 km, as part of the Room for the River IJsseldelta Program commissioned by Rijkswaterstaat and the Province of Overijssel. If not excavated and raised, the wrecks would remain as an obstacle in the river bed and would create an inmediate danger for modern heavy river traffic. For this reason in situ conservation was, although technically possible, not considered a reasonable option.

The Batavialand Foundation at Lelystad will be responsible for the conservation of the cog, the two other wrecks and possibly other valuable objects recovered during the whole operation. Decisions on what to conserve and how will be made by the curators in consultation with an international specialist consultation group directly after the recovery. Conservation of the cog in the purpose-built conservation facility is currently estimated to take three years. The general public will be able to see this work in progress by a built-in stairway looking through windows. After conservation the cog is due to return to its final destination in Kampen, to be displayed as a symbol of the towns Hanseatic heritage. Progress reports will be regularly communicated via the project website, as well as on Facebook and Twitter.

The discovery of the cog by Kampen is important. The ship is one of the best intact examples of a cog to have been discovered in western Europe. The wreck is therefore of great archaeological and historical value, both nationally and internationally. That the wreck was found at a distance of only about 200 meters from the shipyard where the replica the Kamperkogge lies at anchor is also quite remarkable.

The IJssel cog would have been a large seaworthy cargo vessel, with one central mast with a square mainsail. In the 13th, 14th and 15th century this would have been the most common and most popular ship type in northwestern Europe, used in particular by traders and merchants associated with the Hanseatic League . Kampen was the largest Hanseatic seaport in the Low Countries.. Goods were transferred here from river barges to sea going vessels (and the other way around) connecting the Rhineland with trading centres in the Baltic such as Lubeck and Gdansk, Scandinavia and England. These routes took the ships on voyages across the dangerous shallows of the Zuiderzee and Waddenzee, towards the North Sea.

Room for the River IJsseldelta
The Room for the River/Ruimte voor de Rivier IJsseldelta project comprises two different kind of measures to improve the river safety and flood defences in the Kampen-Zwolle region for the next decades. The first of these measues involves deepening the river bed of the Lower IJssel over a length of 7,5 kilometers between de Molen and Eiland bridges. The second measure is the construction of the Reevediep, a complete new side channel of the IJssel, draining into the Drontermeer.

As well as improvements to water safety, the Room for the River IJsseldelta project aims to deliver an important contribution to the environmental quality and spatial planning of the region. Nature conservation areas will be created in five river bank areas. covering 350 hectares of new delta landscape, new walking and cycling routes, a watercourse for recreation as well as a safe new building area for Kampen situated on a so-called climate dyke.

More information?
See the following websites: