Building the world’s longest immersed tunnel requires a number of specially built machines and vessels. One of the most important has now arrived at the construction site in Rødbyhavn after a long journey from the Crist shipyard in Gdynia in Polen. The Immersion Pontoon, which is, in fact, not one, but two vessels that can be assembled and disassembled, has been delivered to the tunnel contractor, Femern Link Contractors, FLC.

Ivy 1 and Ivy 2 have been specifically designed to support the Fehmarnbelt tunnel elements during their journey from the work harbour. When the 217-metre long elements leave the facto-ry, they are light enough to float. However, prior to the immersion process, several thousand tonnes of additional ballast concrete will be added to make the elements heavy enough to be immersed in the dredged tunnel trench on the seabed. From here the tunnel element will only be supported by the two Immersion Pontoons, which will serve as the tunnel element’s 'bathing wings'.

Ivy 1 and Ivy 2 will support opposite ends of each standard element. However, the special ele-ments, which are significantly shorter, will be supported by the two vessels coupled together.

The Immersion Pontoon has two main functions: to support the elements and to control the immersion process. The vessel contains winches with over 200 km of steel wire and a control room from where the immersion process will be managed.

"It will require a steady hand and some highly advanced equipment to immerse the tunnel ele-ments with the precision we require. Our Immersion Pontoon, therefore, has been specially built for this purpose,” says Baris Nacar, Construction Marine Manager, Femern A/S.

Additional technical equipment will be installed over the coming months. The vessel will then be thoroughly tested at sea before the immersion of the first tunnel element can get underway.

FACTS ABOUT THE IMMERSION PONTOON

• Immersion Pontoon was specially built in Poland for the immersion of the tunnel ele-ments.
• The vessel can be split into two depending on what type of element is to be immersed.
• Dimensions: Length 105 metres, width 45 metres (the equivalent of one football pitch)
• Crew 22