The specially designed immersion vessel has passed its final safety checks and won approval from the Danish Maritime Authority after considerable delay, clearing the way for the first elements of the Fehmarnbelt immersed tunnel to be sunk off the coast of Lolland this spring.

The Fehmarnbelt Fixed Link is an under-construction 18km-long road and rail tunnel between the Danish island of Lolland and the German island of Fehmarn. It is being constructed as an immersed tube, which will see precast large concrete elements laid end-to-end on the seabed to create the tunnel.

The element immersion vessel, known as the immersion pontoon IVY, is made up of two joined units, IVY 1 and IVY 2.

For “standard” tunnel segments – each measuring 217m long, 47m wide and weighing 73,000t – each end of an element is attached to one of the units, which provide the buoyancy needed for transport. For “special” elements – each 39m long, 47m wide and weighing 21,000t – the two units are combined to operate as a single vessel.

IVY’s winch system comprises 66 winches and some 23km of steel wire, allowing operators to lower elements to depths of up to 40m with fine control.

Femern Link Contractors (FLC) will place the elements end-to-end with millimetre precision in a specially-dug trench. There will be a total of 89 elements (79 standard and 10 special) adding up to the full 18km length.

Dredging of the trench was completed in 2024 and work to prepare it to accommodate the elements is underway. FLC says it has laid an even gravel foundation in the first section of the trench to ensure a level base for the tunnel elements.

This month, the plan is for IVY 1 and 2 to have the first tunnel element delivered to a jetty at the Danish work harbour. There, ballast concrete will be added to make the element sufficiently heavy to sink. The completed unit will then be taken to the trench and immersed in a controlled operation.

Delays

The Fehmarnbelt project has been delayed by at least two years from its initially planned opening date of 2029. Sund & Bælt, the Danish government-owned company responsible for the project, has said it will publish an updated schedule once immersion of the first elements has begun.

Commencement of the immersion of the elements has been long anticipated. The first tunnel element was cast in May 2024 and the immersion vessels arrived on site in October 2024. Yet, almost 18 months later, not a single element has been submerged – and they have been piling up on site, with 14 standard and three special elements having been cast.

Danish state client organisation Femern A/S (a subsidiary of Sund & Bælt) said the delays were because of issues with the immersion vessels. Due to this, the project recently had to cancel procurement of two major contracts.

Revelations about the tensions between the state-owned client and the contractor were revealed earlier this year. Correspondence between the director of FLC (featuring Vinci, Aarsleff, Wayss & Freytag, Max Bögl and others) and the Danish transport minister – seen by NCE – revealed a blame game about the cause of the delays and the extent of the issues.

With immersion now imminent, all parties are looking to get the project back on track – albeit with a delayed timeframe.

When finished, the tunnel will carry four motorway lanes and two electrified high‑speed rail tracks. The project promoters say it will cut cross‑belt travel times to about 10 minutes by car and seven minutes by train and boost trade and connectivity across the region.

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