Freak waves Flashcards
What are freak waves or “rogue waves”?
Relatively large and spontaneous ocean surface waves that are a threat to all ships, regardless of type or size.
More precisely defined as waves whose height is more than twice the significant wave height (SWH).
What is the definition of significant wave height (SWH)?
The mean of the largest third of waves in a wave train.
What causes freak waves or ‘rogue’ waves?
It is not fully understood what is the cause.
Therefore not necessarily the biggest waves found at sea; rather, they are exceptionally large waves for a given sea state.
Where were freak waves thought to occur?
Only in deep water or where a number of physical factors combine, such as where strong winds and currents meet.
However, recent satellite imagery has shown such waves in comparatively shallow waters like the Baltic.
Reports often refer to freak or rogue waves looking like?
A wall of water.
Meaning they are very steep-sided as well as being very high in comparison to other waves encountered before and after the rogue wave, and possibly preceded by a very deep trough.
What are the areas of highest predictable risk of rogue waves?
Appear to be where a strong current runs counter to the primary direction of travel of the waves.
The area near Cape Agulhas off the southern tip of South Africa.
The warm Agulhas Current runs to the south-west, while the dominant winds are westerlies.
Are rogue waves common?
They are rare events, hence the seafarer can only remain alert to their existence and have strategies in place do deal with one should such a wave be encountered.
Seafarers cam avoid these area, we now know such waves can occur in areas which do not have the characteristics referred to above.
Name examples of casualties attributed to rogue waves.
MS Munchen (mid-Atlantic, December 1978) - lost at sea leaving only ‘a few bits of wreckage’ and signs of sudden damage including extreme forces 20m above the waterline.
MS Louis Majesty (Gulf of Marseille, Mediterranean Sea, March 2010) - an unexpected pack of three waves of 26 feet hit the ship while it was on a cruise between Cartagena and Marseille.
2 passengers were killed in a lounge by flying glass from a shattered window.
Damage to the ship was done by the 2nd and 3rd waves. While these waves were much lower than freak waves appearing in open oceans, published evidenced indicates that their behaviour was similar to that of freak waves.
