Ferries may be causing killer waves

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The Independent Online
HIGH-SPEED FERRIES may face strict speed limits after British scientists demonstrated how the ships can cause huge waves that have been blamed for the death of a fisherman. The Maritime and Coastguard Agency has imposed limits on Seacat ferries, capable of 50mph, which operate out of the port of Harwich. Last month John Sibley drowned when his fishing boat was overturned by a five-metre-high wave.

Mr Sibley's boat was overturned about 10 miles off the coast. An inquest will be held next week, but the Marine Accident Investigation Board has suggested that waves from a high-speed ferry operated by Stena Lines were the most likely cause of the accident.

These waves are also blamed for causing severe erosion on British and European coasts through their exceptional size and power. People living by the coasts of Anglesey in North Wales, the port of Dublin and in Suffolk have already been warned by coastal authorities to beware of the waves, which can rise suddenly from a flat sea.

Now New Scientist magazine has reported that scientists at British Maritime Technology (BMT), a research company, have managed to reproduce the waves in open water. According to Ian Dand of BMT, when a ferry reaches a critical speed their bow produces a "soliton", a solitary wave consisting solely of a peak but no trough. The waves can be devastating, he said.

In deep water the wave may only be a few inches high. But in shallower water it builds up into a mountainous size and, because there is no corresponding trough for it to fall into, the impact is greater than with normal ferry waves.

Tests by BMT found the critical speed falls as the water gets shallower. "In the southern part of the North Sea, which has a depth of between 30m and 40m, the critical speed is about 40 knots," Mr Dand told New Scientist. That is the normal cruising speed of ferries leaving the Harwich port.

Mr Dand thinks that the cause of the solitons is solely due to speed, not shape. An investigation into the effect of changing the hull design found it would not remove the danger: "It looks as though designing the problem out is not going to be possible," he said.