Eatec Engineering Analysis

Analytical Support for the Re-Opened Formal Investigation into the Loss of the MV Derbyshire

Introduction

Following an initial Formal Investigation into the loss of the MV Derbyshire and a  subsequent detailed underwater survey, the Formal Investigation was re-opened in order that the significant new information obtained from the survey could be considered. A number of scenarios leading to the loss of the ship were proposed. Through the Attorney General, Eatec provided analytical support to all parties involved with the Investigation. This involved undertaking finite element analyses of sections of the ship to identify whether the scenarios, as proposed by the interested parties, could have occurred and would have led to deformations and damage as observed by the underwater survey.

The Approach

Detailed finite element analyses were performed on a number of sections of the ship to predict their behaviour under loading conditions corresponding to proposed scenarios. In some instances, it involved calculating the pressure required to cause collapse in order that the sequence of failures could be established. For other sections it involved assessing different forms of loading in order to identify which were consistent with the observed deformations.

The analyses took into account elastic and plastic behaviour of the material and the changes in stiffness as the structures deformed.

The sections analysed included:

  • Main hatch covermv-derbyshire-2
  • Buoyancy tanks
  • Stores deck
  • A main bulkhead
  • Hull plating
  • Fuel tank
  • Slop tank

The Results

The analyses provided significant information, including the following:

  • Main hatch covers would have collapsed and ceased to be watertight under a pressure corresponding to approximately 4.2 metres of water. The Investigation concluded that the hatch covers were likely to have experienced loading in excess of this, and hence flooding of the holds would have occurred.
  • Failure of the stores deck required a pressure corresponding to approximately 42 m of water above the foredeck level, and hence flooding of the fuel tank would not have occurred. Flooding of the bow section, resulting from damage or destruction of the ventilators, would have been limited.
  • The buoyancy tanks would have imploded/exploded by the time the ship had reached a depth of approximately 35 m below the surface, leading to break-up of the ship and free-flooding of many sections. Hence distortions of certain sections of the ship due to pressure differentials must have occurred before the ship reached this depth during the sinking.

The Outcome

The results of the analyses performed by Eatec assisted the Re-opened Formal Investigation in identifying the cause of the loss of MV Derbyshire.

The analyses were able to show that particular events were unlikely to have occurred, and that the predicted structural behaviour resulting from other loading scenarios was consistent with the deformation observed on the seabed, providing additional evidence as to the cause of the loss of the ship.