They are the stuff of legend and maritime myth: giant waves, taller than tower-blocks, that rise out of calm seas and destroy everything in their paths.
For years scientists and marine experts have dismissed such stories as superstition. Walls of water do not rise out of the blue, they said. But now research has revealed that 'killer waves' do exist and regularly devastate ships around the world. They defy all scientific understanding and no craft is capable of withstanding their impact.
'Rogue waves in the past have been ignored and regarded as rare events,' said Jim Gunson, the Met Office's expert on ocean waves. 'Now we are finally getting a handle on them and finding out how common they are.'
These mammoth events are not tidal waves or tsunamis, however. Nor are they caused by earthquakes or landslides. They are single, massive walls of water that rise up - for no known reason - and destroy dozens of ships and oil rigs every year.
The story of the super-tanker München is a classic example. She was one of the biggest ships ever built - the length of two-and-a-half football pitches - and unsinkable, it was claimed.
But on 7 December, 1978, the pride of the German merchant navy, en route to America, disappeared off the face of the earth. Despite the biggest search in the history of shipping, all that was found of the München and her 26 crew was a lifeboat that had suffered an incredible battering.
'Something extraordinary' had destroyed the ship, concluded an official inquiry, which dismissed the München's sinking as a highly unusual event that had no implications for other forms of shipping.
Now scientists believe this calm assurance may be dangerously misguided. The destruction of the München was anything but uncommon, as a BBC2 edition of Horizon, Freak Waves, will point out on Thursday.
'Ships are going down all the time,' said MP Eddie O'Hara, chairman of the parliamentary committee on maritime safety. 'If you read the maritime press there is a boat going down at least once a month, with the loss of crew usually measured in dozens of lives.'
In the past, bad maintenance or poor seamanship were blamed. Now scientists suspect the truth may be far more bizarre.
It is now known that the Queen Mary was hit by a 75ft wall of water while carrying 15,000 troops in December 1942. 'The ship came within an ace of capsizing, but it was all hushed up at the time,' O'Hara told The Observer.
And only two years ago the British superliner Oriana was struck by a 70ft wave that smashed windows and sent water cascading through the ship, swamping six of its 10 decks. A month later eight men were killed when a freak wave struck the Anorient trawler 87 miles west of Loop Head in Co Clare, and two Britons taking part in the world's toughest yacht race last March were seriously injured after a 50ft wave swept over their vessel 70 miles off the Australian coast.
These giant waves cannot be predicted by standard meteorology. Waves - even in the worst of storms - should not reach much more than 40ft. The fact that walls of water up to 100ft are being observed regularly suggests that something is worryingly wrong with meteorology theory.
Waves are normally caused by high winds whipping over the sea surface, but the origin of the freak waves baffles scientists. One theory suggests that waves and winds heading straight into powerful ocean currents may cause these huge walls of water to rise up out of the deep. Another suggests that, under certain conditions, waves can become unstable and start to suck in energy from neighbouring waves and so grow massively and rapidly.
Researchers are still arguing over these ideas, but what is indisputable is the fact that the design of modern ships is inadequate for dealing with the freak waves.
The point will be emphasised this week when O'Hara tables a Commons motion expressing concern over ship safety in freak weather. Hatches need redesigning, he says, while the resistance of windows to the impact of freak waves has to be considerably improved.
Massive improvements - that could cost merchant fleet owners billions of pounds - may have to be carried out on ships if they are to survive the freak waves. 'Ship design is simply not good enough,' said Douglas Faulkner, a Royal Navy ship designer and chairman of naval architecture at Glasgow University. 'Although you can never legislate for everything, you can make the best attempt possible to reduce the risk. The issue of unusual waves is something we really can't ignore.'
