Friday, February 29, 2008

Rogue waves in the news again

I don't know how many of my readers have ever investigated the phenomenon known as "rogue" or "freak" waves. They've always fascinated me, and a recent news report from South Africa has revived that interest. Apparently one person drowned and 18 others had to be rescued after a freak wave hit the beach near Durban, South Africa last weekend. It's not the first time this has happened. Just a few months earlier thirty-foot-plus waves hit the island of Reunion in the Indian Ocean after a storm some days earlier off South Africa. The waves had traveled the thousands of miles to Reunion with their force scarcely diminished. Six people were reported missing after their arrival.

Rogue waves have been rumored and reported for as long as humans have gone to sea, but many European and US scientists were sceptical about them - despite the evidence of damage claimed to have been caused by them. When I was growing up in South Africa they were a regular item on the news as ships would limp into harbor, hulls cracked and torn and cargo (and sometimes crew members) washed away. The photograph below is of a Norwegian tanker that was clobbered by a rogue wave off South Africa in 1974. I saw this ship myself as she lay in Cape Town harbor, waiting for repairs, and was amazed that she'd survived to reach port at all. Authorities stated that one could have driven a double-decker bus through the hole in the bow.

Rogue waves are believed to have caused the loss of countless vessels over the centuries. In South Africa it's widely suspected (although, of course, not proved) that the SS Waratah, which vanished without trace in 1909 off that country's coast, was hit by a rogue wave. If it encountered one as large as that which struck the tanker illustrated above, the much smaller Waratah wouldn't have stood a chance. The MS München, regarded as "virtually unsinkable", was lost in 1978 in what is believed to have been an encounter with a rogue wave during a storm in the Atlantic. It's thought to have damaged her so badly as to render her uncontrollable. There have been many other reported encounters with rogue waves.

The crews of ships that have survived encounters with rogue waves speak of the experience as being like a "hole in the ocean" into which the ship falls, only to be struck by a "mountain of water". The "hole" is, of course, water being drawn into the wave ahead of its passage, thus lowering the water level. If one hits such a combination head-on, one's ship can be in grave danger. Perhaps the most gripping photographic evidence of such dangers was provided by the Chief Engineer of the MS Stolt Surf, damaged by a rogue wave in 1977.

Whilst battling through waves in excess of the usual 10 metre height, she encountered at least one 'freak wave', which towered above the tanker, reaching a height of at least 22 metres and rising above the height of the bridge deck . . . The breaking wave crashing onto the deck and superstructure of the Stolt Surf caused considerable damage. Three of the tank hatches and the door to the pump room were torn off, despite their strong construction. The pipelines running across the decks were bent and the gangways were tossed over the deck and wrecked. Steam pipes and electric cables were torn and ruptured, whilst the wave smashed a number of windows and port holes. Flooding entered the ship, smashing the furniture and tearing off bulkhead panelling. Despite the severe damage, there were no serious injuries, and only one sailor was subsequently hospitalised. The Stolt Surf was fortunate in that her engines remained operational, and the ship was able to remain heading into the waves. Had she lost headway, the storm would have forced her to turn sideways into the oncoming waves, where she risked being hulled or capsized, particularly if she encountered another rogue wave.

In the following photographs of the Stolt Surf's experience, remember that the ship is 556 feet long and 81 feet wide. That gives you a scale for the size of the waves. (Click on the pictures for a larger view.)

A detailed account by the Chief Engineer, with lots more photographs (particularly of the damage to the ship), may be found here. It's well worth reading.

A classic measurement of the rogue wave phenomenon was conducted by US Navy Lieutenant-Commander R. P. Whitemarsh in February 1933. He was in command of the tanker USS Ramapo, crossing the Pacific, when the ship encountered a severe storm. Clearly a cool-headed man, Whitemarsh had his crew take careful measurements of the monstrous waves they encountered (and, fortunately, survived). The wave length was measured at 1,000 to 1,500 feet, with wave periods (intervals) of 14.8 seconds. By careful measurement and triangulation the height of the waves from trough to crest was calculated. The largest was estimated to be 112 feet. That's the height of a ten- to twelve-floor building!

Scientists have only recently begun to investigate the rogue wave phenomenon after actual measurements sparked their interest (particularly the "Draupner Wave" in 1995, recorded at over 80 feet). Recent research has indicated that rogue waves are far more frequent than previously thought. The European Space Agency measured ten during a mere three-week period of satellite surveillance in 2001. There are ongoing research efforts to analyze why they occur, as well as attempts to figure out how to forecast conditions in which rogue waves are more likely to be encountered. South Africa's been doing this for some years, with considerable success.


1 comment:

Firehand said...

I'd heard of these waves before, an amazing phenomenon. Thanks for the pictures and the links.