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Monday, April 14, 2008

Great White Charter Boat Capsizes Off South Africa!

Photo by Terry Goss, copyright 2006. Taken at Isla Guadalupe, Mexico, August 2006. Shot with Nikon D70s in Ikelite housing, in natural light, approx 25fsw. Animal estimated at 11-12 feet in length, age unknown.

A charter boat with 19 passengers aboard capsized off the coast of South Africa yesterday after it was hit by a freak wave while anchored-up. Three people died and 16 were injured.

The boat was taking 10 passengers (there were 9 crew members) to dive with Great Whites. Waters off this area of South Africa are known for Great Whites and Great White diving expeditions.

The AP story can be found here.

Something like this almost happened to me. Ten years or more ago I had a group of six divers on my boat and we were anchored stern-to a ledge called the Western Ear
off of Isle au Haut. I had two anchors out, bow and stern, but had my stern facing the ledge to give my passengers easy access in and out of the boat. I bet conditions were very similar to what they had when this accident happened. Flat calm seas but a slow, greasy swell.

After the dive, while we were having lunch and were all on deck talking and laughing, I heard a foamy growl. I looked up in time to see a very large breaking wave heading for us. I raced to the stern line and let it go and the boat swung around just in time to meet the sea head-to. It was just that one wave but if I hadn't released the stern line it would have pooped us for sure.

It goes to show you how vigilant you have to be even when conditions don't seem to warrant it.

Sub sea seismic activity can lead to a freak wave (tsunami), as can the shearing-off of a big chunk of glacier. Also, ships can cause big waves, particularly naval ships on maneuvers. What happens is the wave energy gets magnified by something called harmonic resonance. Even wind-driven waves can be amplified by harmonic resonance.

If you have any doubts about the power of this phenomenon (harmonic resonance), watch this famous video of the Tacoma Narrows Bridge. It was brought down by the wind.



-seabgb


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