So-called "freak" waves, such as the one believed responsible for the sinking of the Honeydew II, are in fact commonplace. Studies have shown that 15 per cent of waves will be twice the average wave height at any given time, according to an expert from NUI Galway.
Satellite and other studies of the ocean surface have shown that supposedly out-of-the-ordinary waves occur regularly, stated Prof Mike Williams of NUI Galway's department of earth and ocean science. "They found there was an extraordinary number of these waves. The term 'freak' is therefore a misnomer," he said.
"A freak wave is defined as something that is three times the mean wave height at the time of measurement," he said. But statistical analysis of waves using radar have demonstrated that typically about one in seven waves, 15 per cent, will be twice the mean or average height.
Prof Williams looked back through 19th and early 20th century records of wave heights taken by ships at sea. "The amount of 15m waves figures very highly," he said.
It was common for sailors to describe "50ft" or 15m waves "no matter how high the wave is". Accurate measurement of the height of a wave is difficult, particularly as a ship dips down into the deep trough at the edge of an approaching wave. "The thing about these abnormal waves is the trough is frightening. It is not just the height of the wave but the depth of the trough that can damage a ship."
Scientists remain unsure what causes these waves, but one theory suggests a wave moving slightly faster than others catches up with those ahead of it to produce a much bigger wave with a deeper trough.
Exceptional waves have been recorded on the open ocean but are also a common feature along our coastline, he added. "These abnormal waves are responsible for taking fishermen off rocks along the coast."
The angler watches the waves for a time before going to what appears to be a safe distance down the shoreline when a much larger wave comes and sweeps the person away.
Wave data showing the regular occurrence of these waves comes from a range of studies including two from the EU, EuroROSE and MaxWave. These used radar in an attempt to deliver forecasts of "freak" or "rogue" waves. "One wave in about 5,000 will be three or four times the average," at any location, Prof Williams said.
