# Wave Theory

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