Guide 03 stop, check, call
The carbon monoxide alarm went off, or someone feels sick aboard
CO poisoning looks like seasickness. Fresh air first, then find the cause.
Stop first
- Move the person to fresh air at once. The Coast Guard lists irritated eyes, headache, nausea, weakness and dizziness as signs, and says to seek medical attention if necessary. In an emergency call 911 or the Coast Guard on VHF Channel 16.
- Shut down the generator and engines while you find the cause.
- Keep everyone off the swim platform and rear deck, and out of the water near the stern, while any engine or generator runs.
Checks an owner can do
- Do not silence or remove the alarm to stop the noise; treat it as real until the cause is found.
- Note which engines or generator were running, the wind direction, and whether another boat was rafted or idling nearby.
- Read the Coast Guard carbon monoxide page and its checklists before the next trip.
Call a certified marine technician when
- The alarm sounds again with the same equipment running.
- You see soot, water leaks, cracks or loose clamps anywhere on the exhaust system.
- The alarm is past the replacement date printed on it, or chirps a fault (replace it per its maker).
Sources
- Boater's Guide: Carbon Monoxide Hazards (PDF page 38), U.S. Coast Guard Boating Safety Division
- Carbon Monoxide, U.S. Coast Guard Boating Safety Division
- Boater's Guide: VHF MAYDAY procedure (PDF page 47), U.S. Coast Guard Boating Safety Division
Reviewed 2026-10-08. Your manufacturer's instructions come first wherever they differ from this page.
Keep a record and brief your technician
Log this problem on your boat with the checks above as a checklist. Tick what you have done, then print a one-page technician brief: the boat, engine hours, what happens, what you already checked and the boat's recent work. When it is fixed, it goes into your maintenance log.
The technician brief is part of Skipper: $1.95 a month or $19.50 a year. Free during preview. Pricing