“One of the main aims of the preliminary assessment of MV Estonia is to determine the origin of the damage on the starboard side of the wreck. This study provides essential input for the safety investigation authorities in drawing the final conclusions about the cause of this damage,” says Tauri Roosipuu, project leading expert of OJK. “The subject matter of the study commissioned by OJK was to model and simulate the bottom contact of MV Estonia and to assess the structural deformations caused by the bottom contact. The aim was to find out by using calculation, what happens to the hull and its structure when the ship hits the seabed: Will damage occur? How large and what kind of damage will occur? Where will damage occur? And is it possible that newly reported damage can have been caused by the bottom contact?”
“This study is based on a numerical assessment, where the ship descent and the bottom contact are modelled in time domain to obtain the description of structural deformations and damage”, says Professor Kristjan Tabri (DSc), the main author of the study from Tallinn University of Technology. “For that purpose, the digital structural twin of MV Estonia and the surrounding seabed were modelled. Since the seabed around the wreck is highly variable in its characteristics, from very soft sediments to non-deformable rocks, relevant soil parameters were considered when creating the seabed model. To apply a realistic motion kinematics and descent velocity to the numerical simulation, a separate simplified calculation model was developed with the sole aim to evaluate the ship’s descent velocity towards the seabed.”
“The report addresses several challenges in simulating the ship grounding to a deformable seabed at the water depth of about 80 meters. Simulating a ship's contact with deformable seabed is not common nor necessary procedure for the design and normal operation of ships, so in order to do this, it was necessary to develop a method of bringing together the specifics of two separate scientific disciplines, naval architecture and geology in one calculation environment,” says Professor Kristjan Tabri. “In the context of MV Estonia catastrophe, the simulation of the bottom contact of the ship was a first-of-its-kind, in the nineties the initial phase of the accident was simulated up to the loss of stability and in the simulations carried out during comprehensive scientific research in 2000s the ship was flooded up to large heeling angles, but not until it collided with the seabed. Now we have covered the very last phase also.”
Main conclusions of the study are:
- The ship experiences extensive damage due to the bottom contact, even when descending in a nearly statical manner.
- The ship is supported at the middle by protruding rigid acoustic bedrock, while the fore and aft of the ship is supported by softer clay.
- Structural damage is caused both by the soft seabed and by the acoustic bedrock.
- Most significant structural damage occurs at the aft and at the middle of the ship.
- The location of the calculated side damage corresponds well to the location of the reported side damage in the wreck.
- The reported damage has been formed on the edge of the extensive damage located under the wreck (above the fender line).
- The numerical simulations propose a highly probable scenario of the side damages occurring as a result of the contact between the ship and the sea bottom.
An international public procurement was announced by the Estonian Safety Investigation Bureau for the execution of the study. The main contractor of the study was Tallinn University of Technology, supported by the contractors Foreship OÜ and MEC Insenerilahendused OÜ and consulting external partners from Stockholm University (Sweden) and Finland. The contract was signed on 30 August 2022 and the work was delivered on 31 August 2023 at the total expense of 244,850 euros (excluding VAT).
Background info: In 2020 it was discovered that the hull of MV Estonia had suffered damage. As a result of this discovery, a preliminary assessment was initiated by the Estonian Safety Investigation Bureau, the Swedish Accident Investigation Authority and the Safety Investigation Authority, Finland. As part of the investigate activities conducted since 2020, Tallinn University of Technology with its partners has been commissioned to do a research study on the effect of contact with the seabed to the vessel.
