Based on computational modeling by Tallinn University of Technology researchers, a report presented on Thursday suggests that the Estonia's starboard side was damaged by the ship's collision with the seafloor.
The study's lead author, Professor of Marine Structures and Technology Kristjan Tabri, explained that a computational method was used to simulate the ship's sinking and its impact with the seafloor, while assessing structural deformations and damage.
The main finding of the study is that the ship sustained extensive damage as a consequence of the impact with the seafloor, even though the contact was nearly static. The ship was damaged by both soft seafloor and hard bedrock.
The ship's stern and midsection have the most severe structural damage. The location of the damage predicted in the simulation corresponds closely with the actual location of the holes.
Based on the results of the computational modeling, the researchers at the Technical University of Helsinki estimate that the most likely scenario is that the starboard holes were caused by a collision with the seabed.
One of the primary goals of the study was to determine the cause of the damage to the ship's starboard side, said Tauri Roosipuu, lead expert of the Safety Investigation Center (Ohutusjuurdluse Keskus, OJK) project. "The study modeled the collision of the ferry with the seabed and assessed the structural deformations resulting from the collision. Based on calculations, we wanted to find out what would happen to the hull and its structure in the event of such a collision," he explained.
For this purpose, the digital twin of the MS Estonia and the surrounding seabed were modeled. Since the seabed surrounding the wreck has very different characteristics, ranging from very soft sediments to non-deformable rocks, relevant ground parameters were also taken into account when building the model.
In order to simulate realistic motions and sinking trajectory in calculations, a simplified computational model was built solely for estimating the ship's sinking velocity to the seabed. "The study tackles a number of challenges associated with simulating a ship collision with a soft seafloor at a depth of approximately 80 meters. Modeling a ship collision with a softer seabed is neither a common nor necessary procedure in ship design and operation; so it was necessary to device a method for combining the particulars of two distinct disciplines, naval architecture and geology, within a single computational environment," Tabri explained.
Modelling of the damages:
"In the context of the Estonia ferry disaster, the modeling of the ship's contact was the first study of its kind; in the 1990s, the initial phase of the accident was modeled up to the loss of buoyancy, and in the 2000s, detailed models filled the ship with water, but not to the point of collision with the seabed. Now we've reached the final stage of sinking," Tabri added.
To carry out the study, the Center for Safety Investigation launched an international tender. The main contractor for the study was Tallinn University of Technology (TalTech), supported by contractors Foreship OÜ and MEC Engineering Solutions OÜ, and external partners from Stockholm University and Finland. The contract for a total value of €244,850 (excluding VAT) was signed on August 30, 2022, and the work was handed over on August 31 this year.
In 2020, video footage was released showing previously unknown damage to the starboard hull of the ferry Estonia. As a result of this information, the Estonian Safety Investigation Bureau, the Swedish Accident Investigation Authority and the Finnish Safety Investigation Authority launched a preliminary assessment of the new circumstances of the Estonia ferry disaster. As part of the preliminary assessment, Tallinn University of Technology and partners were commissioned to conduct a study on the impact of seabed exposure on ships.
Editor: Mari Peegel, Kristina Kersa