I grew up on the South African coast in an area known for ships vanishing on an all-too-frequent basis. It was part of the lore of the sea and something I came to accept long before I headed across oceans on my own boat. Having a fatalistic bent helps if you are venturing off into the unknown, and for any sailor departing the security of a safe harbor and sailing out to sea is indeed heading off into the unknown. There are simply things out there that remain unexplainable.
I am sure that itís accurate to say that the coast of South Africa has more rogue waves than most areas, and I am equally sure that itís because of the three different, unrelated phenomena that conspire to create them. First there are the prevailing, unrelenting winds kicked up by a never-ending series of low-pressure systems that rotate around Antarctica. North of the lows the wind blows from the west and builds up huge seas that travel unobstructed across the Southern Ocean. The only point of land that sticks down into their path is Cape Horn; however, by the time these waves reach the African coast they have travelled 14,000 miles without obstruction. Rather than big waves, they are gigantic swells with smaller waves forming on their surface.
Whether rogue waves exist and whether you will encounter one is predictable only as a statistical probability, the same as the lottery only with a less desirable outcome. There is a percentage of probability, however small, that one wave somewhere will encounter a series of circumstances that propel it from a large disorganized wave, to a gigantic killer. This does not give much comfort to a sailor with a vivid imagination who is constantly looking over his or her shoulder for "the big one." Still, there are things you can do to prepare yourself and lessen your chances of encountering a rogue wave. The most important thing is to understand waves, what causes them, and how they react when encountering currents or shallow water.
Bob Guza, a professor of oceanography at Scripps Institute in La Jolla, CA, says: "The grouping of waves is even more random than the sizing of individual waves, and not every wave train is the same height. If the average height is 10 feet, you can expect some waves to be half that tall and other to be twice that tall." It is also not always true that the strongest winds create the largest waves. Once the wind exceeds 50 to 60 knots it begins to break the tops off waves reducing their height, and once it reaches hurricane force, the wind actually flattens out the sea. I have been in a hurricane and remember that the wind and rain flattened the seas out quite markedlyósomething I did not expect, but was extremely grateful to see. That hurricane, by the way, was hurricane Lili. We were approaching San Salvador when it hit. Lili was the second hurricane ever recorded in the North Atlantic in December and it arrived on Christmas day, 1984.
|"A consistent wind direction will bring consistent, predictable waves. As soon as the wind changes there is a lag time between the 'old' wave pattern and the new one, and so begins the first opportunity for an odd wave to develop."|
The same thing happens when a counter current meets these wind-generated waves. Instead of the ocean bottom causing friction, or shallow water slowing down the leading waves, the counter current works against the approaching swell in the same manner. The deep water of the current "trips" the swell as soon as the two forms of water meet. The sea becomes the most unpredictable along the edges of the current where the undisturbed waves collide with those that have been affected by the current. When there is a sudden change in wind direction with a new wind blowing perpendicular to the current and the old wind direction, the chance of a rogue wave developing becomes much more likely.
Now that you understand waves and what causes them to become confused and dangerous, your first line of defense as a sailor is to avoid areas where these kinds of waves can develop. For sailors leaving the eastern seaboard of the US, the Gulf Stream should be your greatest concern regarding waves as an obstacle for navigation. Fortunately, the Gulf Stream is a body of water whose current and eddies are well known and can be seen clearly from satellite photos. Before you leave land you will need to get an accurate forecast, and from that you can determine how the wind direction will relate to the direction of the Gulf Stream or one of its eddies. Wind against current, especially if you are sailing into the wind, can lead to a dangerous sea state. You will also need to interpolate how the wind and current will relate to the direction that you are planning to sail. If you are crossing the stream in a wind-against-tide situation, the beam seas can be dangerous and should be avoided. Itís this kind of forethought that can spare you from running into the likelihood of bad seas and the remote possibility of a rogue wave.
|"Wind against current can lead to a dangerous sea state. To be safe, you'll need to interpolate how the wind and current will relate to the direction that you are planning to sail."|
You also need to think about the coastline where you are sailing and how the wind and wave directions will be affected by the land. In this case itís not the shallow water, but rather deep water that is usually accompanied by a high landmass. The backwash off high cliffs is a very real danger and can be felt many miles offshore. If you stop and think for a moment about the number of different scenarios that can develop out at sea, from cross seas to backwash, ships wakes, currents, and shallow water, itís no wonder that on any given day on any part of the vast ocean, a rogue can occur. Itís a matter of averages. For your part, prudent preparation and planning are vital. Be sure that your gear is stowed properly at all times and that your safety gear is ready.
Rogue waves are notorious for arriving without warning and so any prudent mariner will anticipate the worst and be grateful for the best. As Adlard Coles once said, "Reef for the gusts, not the mean." The same can be said for dealing with waves. Expect the 20-footer instead of being lulled by the 10-footers.
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