Technology: Two designs shortlisted in search for safer ferries

2019-02-28 05:06:02

By MICK HAMER IN A WEEK when almost 150 people died in a fire aboard a ferry in Norway, the Scandinavian Star, a research programme commissioned by the British government has shortlisted two devices for improving the stability of roll-on roll-off ferries. The new techniques published in a report are intended to prevent a repetition of the Herald of Free Enterprise disaster of March 1987, which killed 193. The basic problem with roll-on roll-off ferries is that a relatively shallow layer of water on the vehicle deck – the Herald inquiry was told it could be as little as 30 millimetres – would cause the ferry to capsize quickly. The Herald turned over in about 45 seconds. A collision would be the most likely cause of water reaching the vehicle deck. There have been five collisions involving British ships in the past 10 years; one (the European Gateway) capsized rapidly with loss of life. Following the Herald inquiry, the British government set up a research project to improve the stability of ferries. The research consortium, led by British Maritime Technology (BMT), spent two years assessing the technical feasibility of more than a dozen bright ideas, at a cost of Pounds sterling 1 million. The two shortlisted ideas, which researchers say are worthy of further study, are structural sponsons and buoyant wing spaces. Sponsons effectively provide the ferry with a built-in lifebelt, and could be fitted to existing ferries in about two weeks. Buoyant wing spaces are a way of sub-dividing the vehicle deck longitudinally. They increase the stability of the vessel by preventing water from washing across the full width of the car deck, and would make ferries less prone to rapid capsize while still leaving them relatively easy to load. The basic concept has two longitudinal bulkheads running the length of the ship, with transverse bulkheads between the longitudinal bulkheads and the hull. The central space is clear, and could be used for loading lorries. Cars could be loaded into the small wing spaces, perhaps with a double-deck arrangement. The researchers say that this system ‘is demonstrably a very effective way to improve survivability’. The chief disadvantage is the more difficult access for vehicles. The researchers point to problems with other ideas for improving safety. One of the more promising ideas was an inflatable sponson, a kind of emergency lifejacket for a ferry. It consists of buoyancy bags surrounding the hull of the vessel, which would inflate automatically when sensors detect flooding. The report questions the reliability of these sponsons. It says they could not be proven without further development and prototype trials. One of the problems is that the bags might be damaged during docking. A total of six designs incorporating retractable transverse bulkheads were considered by the researchers. A ferry would need about four to five transverse bulkheads for them to be effective in a collision, since a side-on collision might damage one of the bulkheads, effectively putting it out of action. The researchers estimate that the bulkheads would cost shipowners up to Pounds sterling 2.5 million a year because ferries would lose valuable space on the vehicle decks. This would make transverse bulkheads ‘financially very unattractive’ for short hauls, such as the runs across the Strait of Dover. BMT does say that they might be more attractive if they are part of a new design. A team at the University of Glasgow proposed perforating the vehicle deck (so that it could not flood), and providing a double skin all around the hull as a lifebelt for the ship. The idea behind this design is that the ferry would sink on an even keel. BMT says that one of the problems with this design is that the decks would not prevent smoke from spreading in a fire. The researchers also dismiss the idea of ‘washports’, one-way valves on the vehicle deck. As the ferry tips,