Freak waves up to 30 metres high (100 feet) that rise up from calm seas to destroy ships do exist, researchers argue (list).
For centuries sailors have blamed mysterious surges of water for unexplainable sinkings but the claims have always attracted plenty of scepticism.
However, there is now growing evidence, including satellite imagery, which suggests the massive waves may be more than just maritime myth.
New data on the phenomenon, featured by the BBC Science programme Horizon, have led to calls for improved ship designs that will withstand huge water surges.
Walls of water
Every week, a ship sinks to the bottom of the sea, and often there seems no obvious explanation.
These disappearances are usually blamed on human error or the poor maintenance of a vessel.
But in many cases, sailors have their own theory: a single massive wave that appears out of the blue and sinks the ship with one blow.
Evidence presented by Horizon suggests a 43,000-tonne cargo ship, the Munchen - which sank with all hands in 1978 - was struck with huge force.
Several researchers who have studied the event now think a giant wave was responsible.
Although the official inquiry found that "something extraordinary" had destroyed the vessel, it concluded only that the Munchen's loss was a highly unusual event that had no implications for other forms of shipping.
Freak waves are not the same as tidal waves, or tsunamis, and they are not caused by earthquakes or landslides.
They are single, massive walls of water that rise up from apparently calm seas. Several theories compete to explain them.
Some scientists think that waves and winds heading straight into powerful ocean currents may cause a surge of water to rise up out of the deep.
Others believe that some waves can become unstable and start to suck in energy from nearby waves, growing quickly and to huge heights.
Jim Gunson, the UK Met Office's expert on ocean waves, said: "Rogue waves in the past have been ignored and regarded as rare events.
"Now we are finally getting a handle on them and finding out how common they are."
Eddie O'Hara, MP, the chairman of the parliamentary committee on maritime safety, is to table a Commons motion into ship safety in freak weather.
He told the BBC: "Ships are going down all the time. 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."
Remodelling ships to include, for example, new hatch designs to withstand extraordinary waves could cost merchant fleet owners billions of dollars.
- BBCNews : Freak waves spotted from space / Freak wave 'hot spots' identified
- ESA : Ship-sinking monster waves revealed by ESA satellites
- Ifremer : Rogue Waves 2000 / 2004
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