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Rogue Waves- the Economist Sept 17, 2009

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    Rogue Waves- the Economist Sept 17, 2009

    Alan sent me this article from The Economist magazine dated 17 September 2009. He thought we might be interested...



    Monsters of the Deep

    ON JULY 26th 1909 the SS Waratah, en route to London from Melbourne, left Durban with 211 passengers and crew. She was due in Cape Town three days later but never arrived. The steamship was last sighted along the east coast of South Africa—known to sailors as the “wild coast” for its violent weather—struggling through a stormy sea with waves more than nine metres (30 feet) high. No trace of the vessel has ever been found.

    A theory which might explain her disappearance, and that of some other vessels, is that they were struck by rogue waves—which begin with a deep trough followed by a wall of water the size of an eight- or nine-storey building. For many years oceanographers dismissed sailors’ reports of rogue waves much as they did stories of mermaids. But in 1995 an oil rig in the North Sea recorded a 25.6-metre wave. Then in 2000 a British oceanographic vessel recorded a 29-metre wave off the coast of Scotland. In 2004 scientists using three weeks of radar images from European Space Agency satellites found ten rogue waves, each 25 metres or more high.

    A typical ocean wave forms when wind produces a ripple across the surface of the sea. If the wind is strong, the ripples grow larger. A hurricane can amplify a wave to a few storeys. But trying to create giant rogue waves in a laboratory tank is very difficult, making them hard to study. Now researchers led by Eric Heller of Harvard University and Lev Kaplan of Tulane University, New Orleans, have started using microwaves rather than water waves to create a laboratory model.

    Rogue waves are not tsunamis, which are set in motion by earthquakes. These travel at high speed, building up as they approach the shore. Rogue waves seem to occur in deep water or where a number of physical factors such as strong winds and fast currents converge. This may have a focusing effect, which can cause a number of waves to join together. Such conditions exist along Africa’s wild coast, where strong winds blowing from the north-west interact with the swift and narrow Agulhas current flowing down the coast to produce enormous waves. Dr Heller, who likes to sail, says there may be other mechanisms at work too, including an interference effect that causes different ocean swells, travelling at different speeds, to add up to produce a rogue, and a non-linear effect in which a small change in something like wind direction or speed causes a disproportionately large wave.


    To study the phenomenon the group created a platform measuring 26cm by 36cm on which they randomly placed around 60 small brass cones to mimic random eddies in ocean currents. When microwaves were beamed at the platform, the researchers found that hot spots (the microwave equivalent of rogue waves) appeared far more often than conventional wave theory would predict; they were between ten and 100 times more likely.

    Dr Heller says the results tend to support anecdotal evidence from seamen that rogue waves are not as rare as once thought. He thinks the work could also be used to understand more about the formation of these dangerous waves, perhaps to the point where it would one day be possible to provide a warning in places where rogue waves may be prone to appear. Seafarers would be thankful for that.

    #2
    Rouge waves are scary. Very scary. They are like monsters coming out of nowhere, and hits you when you least expect it.

    I have myself experienced a rouge wave and the damages such a wave can cause: on board the Crystal Symphony on a journey between Antarctica and the Falkland Islands. I think I have posted the images before, but will see if I can find the images again and re-post them here.
    With best regards from Jan-Olav Storli

    Administrator and Owner of CaptainsVoyage.
    Main page: http://www.captainsvoyage.com
    Old forum: http://captainsvoyage.7.forumer.com/
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    Surround yourself with positive, ethical people who are committed to excellence.

    Comment


      #3
      Thank Alan for this won't you E, well spotted!
      That 1995 oil rig incident that was mentioned was the Draupner platform. Laser sensor instrumentation actually recorded the event, and this was the first time a measurement of such a rogue wave had been made. As a result, such waves, which had often been dismissed as seafarers' tales, caught the interest of research scientists. Now data from satellites is becoming available (which is how I first became aware of the subject).

      One cause of such waves seems to be where wind driven waves and current are in opposite directions, but there seem to be different types where other factors predominate – such as the effect of shape of coast line which may have some relevance to the North Sea examples. And there is some work on mathematical non-linear models (way beyond me – don’t ask !). Anyway, if such theoretical work and the statistical probabilities are backed up by the increasingly available satellite data, then designing a ship to withstand a smoothly undulating 15m high wave starts to seem inadequate.

      There was an incident involving the Caledonian Star between South America and the Falklands, and also the Bremen somewhere in the South Atlantic. I recollect it was 2001 sort of time, around the period of one of the first research projects using satellite SAR (Synthetic Aperture Radar) data.

      I would like to hear more about your own experience, pakarang.

      Comment


        #4
        Originally posted by Seagull View Post
        I would like to hear more about your own experience, pakarang.
        I think I have posted it somewhere on the old forum, but I shall in any way make a new series of images from that dreadful night when CS was hit so hard - right on the side.
        With best regards from Jan-Olav Storli

        Administrator and Owner of CaptainsVoyage.
        Main page: http://www.captainsvoyage.com
        Old forum: http://captainsvoyage.7.forumer.com/
        Join us: Save the "Kong Olav" on facebook

        Surround yourself with positive, ethical people who are committed to excellence.

        Comment


          #5
          Rough waves are relatively "common" off the South African coast, from abt. East London and NE-ward along the coast, especially along the "100 fathom cote". This is precisely because of strong wind and strong current being in opposite directions.

          In 1981 I was on the pipelayer "LB 200", acting as Floatel in the Statfjord field at the time, with 550 persons on board. During a "freak" storm coming from NE (rather than SW) max. wave height of 23.6 m. was recorded by the wave rider buoy. 120 kts. wind was reported by the Stand by boat, before the Anemometer blew out of his mast.

          We had 12 anchors out and were frantically slacking and heaving on the lines to keep the tension within the break strength of the wires.

          I have been trying to find a picture taken from Statfjord "B", showing "LB 200" with spray covering the Tower.
          It was used in advertisements for some time after, but I haven't been able to find a copy on the web. If anybody know where to find it I would be happy to see it on this forum.

          Here is LB 200 laying pipe in better weather conditions:

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