The oil freighter Esso Languedoc outside the coast of Durban (1980). The man who took it, Philippe Lijour, estimated the mean wave height when this occurred to be about 5-10 m. The mast on the starboard side is 25 m above the mean sea level. The wave approached from behind and broke over deck, but caused only minor damage. Picture from here.
When I started this deep-sea biologist gig, my wife asked me if going to sea be would dangerous. I lied and said no but not that she believed me anyway. A short list includes:
- Falling overboard and being lost at sea
- A submersible failing to return to the surface
- Running out of air in a submersible I
- njury or death due to accidents with large sampling equipment on deck
- A minor or severe injury being complicated by the lack of medical personal at sea
- Rough seas
- And the newly added slicing your abdomen open with a chef’s knife.
I could go on but you should be able to get the picture. Luckily, several precautions are taken and crews trained to avoid these situations. However, the one that fascinates me the most is not necessarily easily prepared for. Rogue waves.
A rogue wave is a large wave that is at least double significant wave height (SWH). SWH is the average height (trough to crest) of the one-third highest waves valid for the indicated 12 hour period (NOAA). They are unpredictable and can provide a significant threat to the largest of vessels. Largely rogue or freak waves, much like the kraken, are fodder for ocean lore based in reality. The most well-known and well-documented rogue wave is the New Year Wave recorded in the North Sea at the Draupner oil platform on January 1st 1995. The current SWH was 12m (39ft) with the New Year Wave being recorded at 18.5m (61ft). The EU funded the MaxWave project also using satellite data recorded signatures of several rogue waves.
The National Weather Center’s Ocean Prediction Center (NOAA) lists three potential hypotheses to explain the formation of rogue waves.
- Constructive interference. Multiple wave trains of differing strengths and directions intersect producing a short-lived summed wave.
- Focusing of wave energy. Storm generated waves form counter to the normal wave direction that shortens the wave frequency. The superimposed wave trains lead to a longer lived rogue wave.
- Normal part of the wave spectrum. The complexity and multitude of factors generating waves produce the full spectrum of wave sizes. The smallest waves, capillary, occur with a greater probability than the largest waves, rogue.
There are numerous rogue wave reports including this report of rogue wave slamming into a Gloucester dragger. Other rogue waves hit Acapulco this month and a 49ft sailboat off Florida. The most troubling report for me is the account published in the peer-reviewed Geophysical Research Letters of an incident in 2000 that occurred to British oceanographic research vessel west of Scotland that experienced the largest waves ever recorded by scientific instruments in the open ocean. Under severe gale force conditions with wind speeds averaging 21 ms-1 a shipborne wave recorder measured individual waves up to 29.1 m from crest to trough, and a maximum significant wave height of 18.5 m. The fully formed sea developed in unusual conditions as westerly winds blew across the North Atlantic for two days, during which time a frontal system propagated at a speed close to the group velocity of the peak waves.
More at (and photos from) Freak waves, rogue waves, extreme waves and ocean wave climate