FEATURE
WEATHER ROUTING
Rogue Waves
Detection and Avoidance
Sailors have passed down the stories of rogue waves for centuries. Once thought to be untrue by scientists, significant evidence shows they do occur, and in fact, occur more frequently than was first thought. The Queen Elizabeth 2 encountered a rogue wave of almost 100 ft. in 1995. "At 0410 the rogue wave was sighted right ahead, looming out of the darkness from 220 degrees, it looked as though the ship was heading straight for the white cliffs of Dover. The wave broke with tremendous force over the bow." (Grabianowski, 2008) Another example is when a rogue wave hit the Draupner oil platform in the North Sea on January 1, 1995, causing minor damage (Clauss, Stutz, Schmittner 2004). This is known to be the first official recording of a rogue wave. Also, in January of 2005, the research vessel Explorer was heavily damaged after it was hit by a 50 ft. rogue wave in the Pacific, knocking out three of its four engines and injuring two crewmembers (Grabianowski, 2008). The two main unknowns of rogue waves are how they form and how often do they occur.
Definition
Rogue waves are defined as waves that are more than twice the size of significant wave heights. Significant wave height is the average height of the highest onethird of the waves (Grabianowski, 2008). Rogue waves are also described as freak waves, monster waves, or extreme waves and can reach heights of 100 ft. or higher.
Rogue waves most commonly occur across strong currents, like the Gulf Stream, Agulhas Current and the Kuroshio Current. Also, strong winds associated with gales, storms, tropical systems, or frontal boundaries over a large fetch can create large waves and also possible rogue waves (Muller, Osborne, Garrett, 2005). Typically, rogue waves occur north of 30N and south of 30S due to gales and storms developing mostly in the higher latitudes. Rogue waves are not necessarily the biggest waves found at sea. By definition, a set of waves at eight ft. in an area where the significant wave height is two ft. can be considered rogue waves, however our concern is with rogue waves of 30ft or higher. Rogue waves also tend to be steeper than most
waves (Grabianowski, 2008). Captains who have claimed to see rogue waves describe it as a "wall of water".
Classifications
There are three types of classifications of Rogue Waves; Singular Wave Tower, Three Sisters, and White wall. Singular wave towers are generated by constructive wave reinforcement, which is when several different waves of different speeds and directions meet at the same time. Three sisters is the theory that rogue waves come in sets of three. Captains commonly use this term, though there is no scientific evidence to support this theory (Ocean Prediction Center). White walls develop when wind driven seas from one direction interact with swells
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Maritime Reporter & Engineering News