Headache on a boat: seasickness, or the engine?
A headache on the water usually has a dull cause: sun, glare, no water since breakfast, or the early stage of seasickness. There is one exception worth knowing before you go afloat. Carbon monoxide from an engine or a generator produces headache, nausea, dizziness and weakness, the same short list as seasickness, and on boats it is regularly mistaken for it.
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Why this happens on a boat
Exhaust gathers in enclosed spaces: a cabin, a cockpit with the canopy zipped up, the pocket of air under a swim platform, anywhere downwind of a running generator. You cannot see it or smell it. The pattern is what gives it away. Seasickness follows the sea, so it eases when the water flattens and stops once you are ashore. Carbon monoxide follows the exhaust: better in clean air, worse again in the same spot, and it commonly affects several people at once, including the ones who never get seasick.
What to do right now
- 1
If a headache starts while an engine or generator is running, get everyone into clean moving air first and ask questions afterwards.
- 2
Shut the generator down and move away from any exhaust outlet.
- 3
Count heads. Several people with headache, nausea and weakness at the same time is a carbon monoxide pattern, not a seasickness one.
- 4
Call for help if anyone is confused, unsteady, very drowsy or short of breath. Carbon monoxide poisoning is an emergency and needs medical oxygen, not fresh air alone.
- 5
If nothing is running and the headache tracks the motion, treat it as travel sickness: shade, water, a view of the horizon, and a session through any headphones for about 90 seconds.
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Preventing it next time
- Fit and test a carbon monoxide alarm in any boat with a cabin, a canopy or a generator.
- Never run a generator while people are sleeping aboard, and keep sleeping spaces well away from exhaust outlets.
- Ventilate the cabin under way. A following wind can pull exhaust back into the boat at low speed.
- For the ordinary causes: sunglasses, a hat, shade, and water before you feel thirsty.
When to see a doctor
Get emergency help for a headache afloat that comes with confusion, drowsiness, collapse, chest pain or breathlessness, or that hits several people at the same time. Ashore, see a doctor about headaches that keep returning after trips, one sided throbbing with light sensitivity, or any headache that is the worst you have ever had.
Common questions
How can I tell seasickness from carbon monoxide?
Look at the pattern rather than the symptom. Seasickness follows the sea: worse in a swell, better when it flattens or once you are ashore, and it picks on the people who are prone to it. Carbon monoxide follows the exhaust: it improves in clean air, returns when you go back to the same spot, and often hits several people together.
Do I really need a carbon monoxide alarm on a small boat?
If it has a cabin, a canopy you zip shut, or a generator, yes. The gas has no colour or smell, the early symptoms look like ordinary travel sickness, and the people most at risk are the ones lying down out of the wind.
Is a headache on a boat always motion sickness if the water is rough?
No. Glare, dehydration and skipped meals cause plenty of headaches afloat, and travel is a common migraine trigger. If there is no queasiness with it and nothing is running, start with shade, water and food before you blame the sea.
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Medically informational; not a substitute for a doctor's advice. Persistent or unusual symptoms deserve a clinical evaluation.