Seasickness

Motion sickness caused by conflicting signals from the inner ear and eyes on a moving boat; it costs divers fluids, comfort, and sometimes the dive itself.

Seasickness is motion sickness triggered by a boat's movement: the inner ear reports rolling and pitching while the eyes, fixed on a stable deck or cabin, report stillness, and the mismatch produces nausea, cold sweats, yawning, salivation, and eventually vomiting. For divers it is more than misery. Vomiting drains fluids and worsens dehydration, a recognized decompression risk factor, and a badly seasick diver makes poor decisions during gear-up and may abort the dive entirely. Interestingly, most sufferers improve dramatically once underwater, where the motion largely disappears.

Managing it starts before the boat leaves: take proven medication such as dimenhydrinate, meclizine, or a scopolamine patch well before departure, following the label and ideally after testing it on land for drowsiness, since sedation and diving mix poorly. On board, stay on deck in fresh air, watch the horizon, keep to the boat's midline where motion is least, avoid reading and screens, and skip greasy food and alcohol the night before. If it hits anyway, vomit downwind, rinse, and rehydrate.

Divers prone to it learn their own playbook: gear up early before concentration on tasks below deck triggers nausea, be first in the water rather than bobbing at the surface waiting, and choose shore dives or larger, more stable boats when serious swell is forecast. Noting sea state and how you felt in the dive log helps you spot your personal threshold.