ASK THE GREAT NAMAZU
Namazu, Giant Catfish and Former Japanese Demigod turned Analyst Answers your Questions Great and Small. "In Depth Answers" from the "In Depth Source."
A READER ASKS: Namo? What do they mean by a "freak wave"?
NAMAZU RESPONDS: Dude, that depends on who "they are"? If its some crew boat skipper who was driving his boat too hard for the sea state , or his lawyer trying to answer how a passenger was injured anything can be a "Freak Wave'. So let's concentrate on what science calls a freak wave and what the law ought to call it. I think law and science can probably agree on this definition:
"A 'Freak Wave' may be defined as a wave out of proportion to the observable sea state of such magnitude that an ordinarily trained and prudent mariner would not anticipate its presence in the sea state".
OK, keep you eye on the words " ordinarily trained and prudent mariner", its what the professional mariner wouldn't foresee, not what some landlubber thinks is freakish. So to know what a professional seaman must know about sea states and wave trains we have to go to standards of training and examination. That's where we find the 'Beaufort Scale" which seaman are trained and examined in. News flash, according to the Beaufort scale seas are ordinarily "confused" meaning that any Beaufort Scaled Sea State ( they're numbered) has an average wave and a predictable percentage of waves within a predictable range higher and lower than the "average". The difference can be quite large and the coincidence of the smaller waves followed by the larger rather than an average wave is quite ordinary, but if you aren't operating your vessel at a speed prudent relative to this largest predictable difference, you didn't hit a "freak wave", you are just a negligent deck watch officer running too fast for the sea state. Let me give you an example; based on using table 11-8 of Beaufort, we find that if a wave train has a "significant" wave height of 10 feet, the highest wave in the train is going to be 18.7 feet, the average highest 10 percent is 12.9 feet, and the mean wave height is only 6.4 feet. So the 10% of the waves that your vessel is plowing into are twice the size of the mean, and the highest is going to tower almost 12 feet higher than the mean. This is predictable by any ordinarily trained seaman and not freakish.
To an oceanographer a true freak wave is generated by seismic activity or other unusual hydrodynamic forces. The height difference between the true "freak wave" and the dominant sea state sea state is vast, far more than anything that can be computed using the Beaufort Scale. We do know today thanks to satellite imagery that these waves occur somewhere in the World's oceans almost daily, but only a few and their intrusion into the normal shipping lanes is a mathematical oddity.
So my land lubbing biped friend, "freak waves" are really freakish and rare. The "freak wave" defense against negligent ship or boat handling in admiralty court is common as dirt. It only works when the opposing lawyer is a land lubber.
And Who is "Namo" ? I am....
NAMAZU , The Earth Shaker ( You don't have to always add the formal title, I'm retired from the demigod business, Namazu is fine. I've only had various titles, never a real last name, but give me a break I'm 3,000 years old and size of Japan I'm due at least the respect due one's elders. I am not "Namo" you obviously over indulged, irreverent, under educated, uncultured American biped.)