What it is: The instantaneous result of the meeting of two or more waves of different sizes moving generally from the same direction.
Likelihood of encounter: Slim.
Chances of survival: Not good.
What to do: Hail Mary, she's on Channel 16. "The power of the boat or its direction has nothing to do with it, nor do the boat-handling skills of the captain," says William Van Dorn, professor emeritus at the Scripps Institution of Oceanography. "You're just a cork on the water that's going to tumble."
What it is: Occurs in areas where bottom topography constricts the mouth of an inlet or bay, funneling and accelerating water. When the tide is ebbing and opposing large surf, huge waves can build.
Likelihood of encounter: Good.
Chances of survival: Excellent.
What to do: Buy a tide book and use it. "Go out only when Mother Nature wants you to," says Arthur Shelton, who's been transiting California's Tomales Bay in a variety of fishing craft for 30 years. Like most narrow inlets, Tomales has shifting sandbars. Always know where the bars are, that's also where the breakers are likely to be. Even when the water over the bars is calm, they are prime places for sneaker waves (mini-rogues) to show up. "The main thing," adds Shelton, "is to not try crossing in or going out alone as a first-timer. Go with somebody who's done it and knows."
What it is: Small, short-period (the time in seconds between peaks) waves that can raise havoc in a restricted waterway or when you're too close to their source.
Likelihood of encounter: Certain.
Chances of survival: Almost guaranteed.
What to do: Try to take wakes on your bow. If they hit you from the side, you can capsize, and if they come from the rear, you can ship a lot of water. Boaters who fish inside Oregon Inlet north of Cape Hatteras, where wakes bounce off the shore and themselves, keep their engines idling so they can maneuver quickly. "Commercial boat traffic and some of the good ol' boys can make a mess of the place," says Larry Haack, who runs a Web site devoted to Oregon Inlet swampings. "During peak traffic hours boat wakes can come at you from several directions at once." Boaters here subscribe to the "smaller the boat, the bigger the bilge pump" rule. "We all use at least 2,400-gph pumps with 1 1/2" hoses," says Haack. So-called self-bailing cockpits should never be depended on and are no substitute for well-maintained bilge pumps. He also advises that you "always know where the deeper water is and have an escape route planned from wherever you are."
What it is: Where rivers empty into oceans, waters collide in constant combat. The bottom gets shifty and forms ever-changing sandbars that can cause waves to break.
Likelihood of encounter: Good.
Chances of survival: Depends.
What to do: See tidal jet rule (above) about not trying it as a first-timer. Boatswain's Mate Second Class Kyle Betts of the Cape Disappointment Coast Guard Station at the mouth of the Columbia River in Oregon, recommends calling your local Coast Guard station by phone or on Channel 16 to get the latest conditions of the bar. To find out what's going on offshore, you can access NOAA weather buoy information (seaboard.ndbc.noaa.gov). Betts says recreational boaters should only cross a bar during a standing or incoming tidal current. "A flood tide will help flatten out and space the wave periods better," he says. "On the ebb wave, periods can shrink, causing waves to slop over. But on the flood, waves will get rounded instead." Try to look ahead three or four waves, so you can apply the main goal of wave theory: no surprises.