Results released: The fuel tanks of coastal defence ship Ilmarinen can be emptied in a controlled way

Coastal defence ship Ilmarinen sank on 13 September 1941. The current estimate is that its tanks hold a total of 100,000 litres of light fuel oil.

The results of the expedition investigating the condition of the wreck and the location of the fuel tanks helped to shed light on how best to remove the fuel safely. At the moment, the wreck is leaking a couple of drops per minute. The wreck is covered by a fairly thick layer of corrosion. One risk of the riveted hull is it splitting, which could result in a larger oil spill. This would be particularly disastrous for the nearby Archipelago National Park.

The current state of the wreck was examined with the help of a remotely operated vehicle (ROV) and divers. ROVs are diving robots used to locate and photograph underwater objects. ROV imaging was used to map out the locations of tanks containing oil, which will facilitate a potential oil extraction operation in the future. Imaging was also used to examine the condition of the hull of the wreck and the damage to it. The investigation also made use of remotely controlled imaging devices, hydroacoustic equipment and ultrasound measurements.

Tommi Kontto, Project manager at the Finnish Environment Institute, describes the findings of the investigation as follows: “Corrosion was removed from the surface of the hull in a few spots, revealing an intact steel surface underneath. The hull is riveted, and corrosion can affect the rivets in the seams and the steel sheets in different ways. The oil in Ilmarinen’s fuel tanks is a risk to the delicate and vulnerable Baltic Sea. Based on the results of the investigation, we estimate that the fuel tanks of the wreck can be emptied in a controlled way before the oil leaking from the tanks poses a greater risk to the marine environment.”

A moment of silence on site in memory of the marines who lost their lives

When Ilmarinen struck a sea mine off the shore of Utö on 13 September 1941, 271 marines were killed in the accident. The sanctity of the grave was one important consideration when planning the investigation. The planning process for the dives involved conversations with the heritage association upholding the legacy of coastal defence ship Ilmarinen, the ecclesiastic representatives of the Defence Forces and the Regional State Administrative Agency responsible for the sanctity of the grave. None of them saw any obstacle to proceeding with the investigation. Before the start of the operation, a moment of silence was held at the investigation site in memory of the marines who lost their lives.

In the wreck, divers did not enter spaces that hold the deceased. The examination of the wreck was superficial and non-invasive.

Draining the fuel tanks of the wreck planned for 2025–2026

The Ministry of the Environment is cooperating with other authorities to support emptying the fuel tanks of the Ilmarinen shipwreck as a joint authority effort. The goal is to extract the oil from the sunken vessel in 2025–2026. The removal of oil from the wreck is funded by the Ahti water protection programme of the Ministry of the Environment (2023–2027). The programme implements the objective of Petteri Orpo’s Government Programme for the protection of waters and the Baltic Sea.