Seasickness, sometimes referred to as "mal de mer," is the mariner's most common ailment, and among the most dreaded. Susceptibility is virtually universal. Untreated, seasickness leads to rapid physical and mental deterioration, posing a major hazard to crew health, safety and morale. As anyone who has been seasick knows, it is an illness to be reckoned with.

Seasickness results from a mismatch of sensory inputs processed by the brain's balance center to help orient the body's position. Place someone in the cabin of a heeling and rolling boat, and you immediately invite mal de mer. Below decks, the eyes are oriented to the floor and ceiling and detect no tilt. But fluid in the inner ear shifts with the boat's motion, sending a different position signal to the brain. Sensors in the neck, muscles and joints relay additional information, depending on how the person moves.

The conflict of sensory data from all these sources ultimately activates a series of responses we recognize as seasickness, especially the intense nausea and vomiting. The trick to preventing seasickness is to avoid sensory conflict by coordinating the sensory input, especially between your eyes and ears. Simply put: If your eyes are seeing what your ears are feeling, you are going to have a great day at sea. If not, you may want to find the nearest railing.

PREVENTION

You want to minimize the time you're going to spend below decks while underway. That requires some pre-trip preparation. Try to bring the things you will need, such as chart books or binoculars, to the cockpit or flying bridge before you leave.

It's always best to stay in the fresh air, away from engine fumes, and near the center of the boat, where motion is less pronounced. Try to keep your eyes on the horizon to provide a stable reference point. Sit or stand upright with your head and upper body balanced over your hips, and anticipate the boat's motion as though "riding" the waves.

Standing and taking the helm will help you accomplish this by reducing sensory conflict. Steer the boat by reference to the horizon, clouds, oncoming waves and distant marks. When possible, avoid close-focused visual tasks such as reading charts, working on computers and studying the screens of navigation instruments.

The same advice given to pregnant women trying to stave-off nausea also holds true here: Nibble on saltines and sip water or juice.