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Abnormal Waves

Agulhas Current - February 23, 2008

There are three major contributors to green faces on board the ship yesterday.

    1. We're right smack dab in the Agulhas Current, which is one of the strongest ocean currents on the entire planet. Running mainly from northeast to southwest, in some places it's as fast as 6 knots. Knots, or nautical miles per hour equal miles per hour times 1.15, so we're talking a current that's about 7 miles per hour, which is pretty damn swift.

    2. This Southern Africa region is also characterized by variable weather patterns - low and high pressure systems that move from the South America's Atlantic coast to the eastern seaboard of the South African one. At 1pm yesterday afternoon, which was about the peak of my trauma, the South African Weather Service predicted "Heavy Seas: Very rough seas with wave heights in excess of 5m expected over the southern half of the Mozambique Channel with "cyclonic" gale force winds of 30 to 35 in the south.

    3. Between Durban and Port Elizabeth, two lovely South African cities, there aren't any “sheltered harbors or anchorages,” meaning we can run but we can't hide.



Even if we can't hide, the ship is outfitted with stabilizers for just this type of situation. They are basically fins mounted beneath the waterline. I believe ours may even be "gyroscopically controlled” or “active fins" that change angle to combat the roll caused by wind and waves, but I haven't confirmed that. What I have confirmed is that I hate to imagine how we'd be doing without the stabilizers.

One other factor is at play: we are in an area prone to giant, rogue or so-called "abnormal waves." In their book Basic Ship Theory, Rawson and Tupper note that "Abnormal waves can be created by a combination of winds, currents and seabed topography. A ship may be heading into waves 8 m high [we had a few at 7 m today and have been encountering 5 m waves most of the day. We're talking 16 to 23 foot waves, my friends] when suddenly the bow falls into a long, sloping trough so that in effect it is steaming downhill. At the bottom it may meet a steep wall of water, perhaps 18 m high and about to break, bearing down on it at 30 knots." These "monstrous, freak" waves can be devastating.

I feel calm because my stomach has ceased to churn, although I wondered if I shouldn't take some Dramamine before going to bed so I that I wouldn’t wake up in the same dire straits (no pun intended) as I had the previous morning, I decided not to and was fine.

Posted by mpho3 07:59

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