Wave Theory | Boating Magazine

Wave Theory

A rogue's gallery of rollers and how to handle them.

Wave Theory

As our boat accelerated toward the curling lip of an out-of-nowhere wave, time got rubbery. We cleared the breaker just before it crashed and discovered why boats weren't meant to fly. As two airborne seconds stretched into eternity, the ride turned eerily smooth, and the naked propeller allowed the engine to scream as all three of us floated above the deck like an animated Dali painting. Legs and hands searched for a secure hold as the boat rolled to starboard. Splashdown came with such a jolt, it's a wonder the boat didn't shatter. Somehow only one of us - me - got hurt. But what's a few fractured ribs in exchange for an "I survived a rogue wave" bumper sticker?

That was last May. A few months later, another sneaky roller bagged me - and in the same location, off Point Loma in San Diego. Both times the waters were choppy but not overly rough. We were above a 50-foot bottom, with the wave moving up on us astonishingly fast. And both times everybody onboard started babbling about rogue waves. My wife is positive that my rogue wave stories are a cover for hotdogging too near the surf zone. To her, and many others as well, the existence of colossal walls of water that come out of nowhere remain a quaint legend of the sea, like the Green Flash at sunset (which I can also personally vouch for).

Even the law holds rogue waves in the realm of mythology. A man who blamed a rogue wave for the mysterious disappearance of his millionaire wife - a competition swimmer - was spinning a fishy alibi, concluded the Orange County, California, district attorney. Eric Bechler maintains that his wife was towing him on a body board behind a rented 19' runabout four miles off Newport Beach in 1997 when a rogue wave knocked him off the board. When he came up, the boat was circling and his wife gone. After two years of chin scratching, prosecutors finally charged him with murder.

His story may be a scam, but what if he's telling the truth? And what if the jury doesn't buy it? For Bechler, who has pleaded not guilty and is awaiting trial, and us boaters as well, the validity of his story - and rogue waves - could mean the difference between life and death. And if they do exist, is there a way to survive them?

THEORY AND REALITY

The hair on the back of my neck didn't rise until I called Richard Seymour, a research engineer who teaches at the Scripps Institution of Oceanography's Center for Coastal Studies, San Diego, California, to talk about different types of waves and how small boats should best approach them. When I asked him if he ever saw a rogue wave, he answered yes - once off Point Loma, in the same vicinity as the one that has it in for me.

For him and most oceanographers, the idea of a rogue wave is no joke. "This is a wave that a good seaman wouldn't anticipate," explains Seymour, who helped assemble the Coastal Data Information Program (CDIP) Web site (cdip.ucsd.edu), which uses weather buoy data to model and predict inshore wave activity along the West Coast. Although some oceanographers maintain rogue waves occur only during intense storms, the term has been extended to include any freakish wave that's substantially larger than the surrounding seas.

So how likely is the average recreational boater to encounter a rogue wave? A classic rogue, the kind that peaks up to 75 or 100 feet, smashes the bridge windows of supertankers, and turns aircraft carriers into surfboards, generally occur only in storms. Bluewater mariners can go a lifetime without seeing one.

On the other hand, there was that 18'-high, 27-mile-long wave that lurched up out of the Atlantic on the night of July 3, 1992, smashing hundreds of cars and injuring 75 people in Daytona Beach, Florida. But seismologists attributed it to an undersea landslide. If it had happened during the day, dozens of boaters would have gotten an instant lesson in tidal wave seamanship.

A true rogue results when two or more waves of different sizes, moving generally from the same direction, meet at one point for an instant. "It's like rolling the dice," explains William Van Dorn, professor emeritus at the Scripps Institution of Oceanography, whose book, Oceanography and Seamanship, is a bible for offshore boaters. "An accumulation of waves into a rogue, which always breaks, is a random occurrence."

NUMBER CRUNCHERS

The combining of waves is not completely unpredictable, though. Statistical analysis within wave theory can relay an idea of your chances of encountering the most extreme waves in a given sea state. A researcher, cited in another oceanography classic, Willard Bascom's Waves and Beaches, demonstrated that one wave in 23 is twice the height of the average wave in a fully developed sea. One in 1,175 is more than three times the average height, and one in 300,000 runs more than four times the average. You can encounter a lot of waves in a long day of fishing. Last item on the boating checklist: lucky rabbit's foot.

Van Dorn, who has performed numerous studies, worked out a diagram illustrating time expectancy of encountering breaking waves high enough to capsize or pitch-pole (pile driving or cartwheeling a boat bow to stern) a vessel of a given length in a given wind speed. This diagram was based on wave basin tests which showed that a breaking wave as high as a boat's overall length could pitch-pole the boat. Similarly, if the boat is sideways to the waves, it only takes a wave whose height is equal to or greater than the boat's beam to capsize it. According to his "catastrophic probability" diagram, in a 30-knot wind in a fully developed sea you might hit a 30' breaking wave about once every hour. Wind is the key element here as waves are nothing more than wind energy stored in water. Higher winds equal higher waves, unless the wind is blowing against them. In that case, opposing winds tend to flatten and cancel out oncoming waves. "You just have to keep looking in every direction all the time," advises Van Dorn, who was a technical consultant during the filming of The Perfect Storm. "A freak wave can pop up anywhere, any time."

Of course, Seamanship 101 says you need to point your nose into, or just off, a wave to avoid taking it from the side and risking a capsize. But boat speed is also critical. Too fast and you might go airborne off the lip. Too slow and you risk a wave breaking over your bow. Shipbuilders have a formula: The force of impact equals the square of the sum of the velocity of the wave and the boat. In other words, a boat traveling 40 mph meets a wave going 20 mph, the force of impact equals, 3,600 ft-lbs. Lower your speed to 20 mph, and the impact reduces to 1,600 ft-lbs. Moderate speed is the key. Otherwise when a wave breaks over the front of the boat, it will likely be a life-altering event.

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