The complexity of the diesel electric propulsion arrangement was highlighted last week during an industry forum hosted by the DNV London Maritime Service Centre. Representatives from major shipowners, enginebuilders and pod manufacturers were present.
With the diesel electric concept gaining favourable ground in newbuildings, especially the cruiseship market, concern is such that this heavily integrated, software-dependant configuration is still not fully understood. Lack of knowledge and a reliance on software are cited as causes that could lead to single failure and a ‘dead’ ship.
Speaking at the event in London, Gro Paulsrud, DNV’s head of section MTPNO371, argued that complexity significantly increases the potential for human error and that the functionality of these [integrated diesel electric] systems is not fully understood by operators. ‘They are not being operated as intended. Automatic systems are being operated manually and knowledge of how to recover systems is still not appreciated,’ she said, highlighting a number of accidents or near accidents that started with one single failure resulting from operational error.
Interface problems
Paulsrud contended that many of the interface or software problems observed are due to the glut of equipment suppliers, continuous software upgrades and the fact that there is no one standard diesel electric configuration. She suggested that improvements could be made with the introduction of a full integration plan, standardised machinery and machinery interfaces and the provision of better software specification, testing and traceability.
A common theme throughout the forum was propulsion redundancy and a number of presentations were made that linked its importance to reducing the consequence of operational error. However, despite the fact that more components could increase the potential for failure, Alf Kåre Ådananes, technology manager with Azipod manufacturer ABB, believes that the ‘diesel electric solution offers greater flexibility when it comes down to redundancy and safety can be further increased by introducing a firewall between the two propulsion lines’.
True redundancy
Indeed a question from the floor emphasised the relevance of redundancy without such a division: ‘True redundancy is not only about computer systems, engines and motors. It is also about the physical layout of a ship. There is absolutely no point in having machinery redundancy if all the equipment is in one compartment. There should be twin compartments as a fire could make the redundancy redundant!’
Despite some well documented ‘teething problems’, Knut Skeisvoll, senior superintendent, Royal Caribbean Cruise Lines (RCCL), who has been responsible for the installation of diesel electric propulsions systems in 25 RCCl newbuildings, is still a keen advocate of the concept and explained that the cruise line has also focused on having completely separate shaft lines.
‘I am convinced that electric propulsion is an excellent opportunity and it is here to stay, although we must find a solution to the problems we have faced,’ he said.
DNV, which has a notation for redundant propulsion, defines redundancy as ‘the ability of a component or system to maintain or restore its function when one failure has occurred and that this can be achieved by component redundancy or system redundancy.
