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FINDINGS LIBRARY · GAS AND SAFETY

No CO alarm on a boat: what ABYC A-24 asks and how surveyors report it

UPDATED 5 NOVEMBER 2026 · 3 EXAMPLE FINDINGS · 1 SOURCES

Where a boat needs carbon monoxide detectors under the revised ABYC A-24, which detectors qualify, where not to fit them, what a surveyor checks and three example findings graded A, B and C.

AT A GLANCE
No CO alarm
USUAL GRADE
A for no CO detector in a cabin used for sleeping on a boat with a generator, engine or cabin heater. B for a detector past its replacement date or not rated for boats. C for a detector badly placed
FOUND WITH
Looking for a detector in each habitable space, reading its label for the standard and the replacement date, and pressing its test button
JUDGED AGAINST
ABYC A-24, in its latest revision, which asks for CO detectors monitoring every habitable space, tested to UL 2034 including the sections for recreational boats
REPAIR COST
The detector and fitting time. Replace each unit before the date marked on it

Carbon monoxide has no smell or colour. On a boat it comes from engines, generators and fuel-burning heaters and cookers, and it collects in cabins where people sleep. A detector is the only warning, which is why a cabin boat without one gets a finding.

What the standard asks

ABYC's A-24 covers carbon monoxide detectors, and its latest revision is built around habitable spaces. In ABYC's own summary: detectors must monitor the atmosphere in habitable spaces, meaning spaces used for sleeping, cooking, eating, navigating or steering, and washing or the heads. Storage lockers, open cockpits and engine rooms don't count. Detectors must be tested to UL 2034, including its sections for recreational boats.

ABYC also says where not to put them: anywhere they could be damaged, anywhere the sampled air is diluted, such as beside hatches, ports or ventilation openings, and in corners with poor air circulation. And replace each unit before the date marked on it.

How a surveyor checks it

Walk through each habitable space and look for a detector. Read the label: the standard it meets, whether it's for marine use, and the replacement date. Press the test button. Then look at the sources: a generator, a diesel heater, a gas cooker, and how the exhaust leaves the boat. A cabin boat that sleeps aboard with a generator or heater and no detector is the A.

Placement matters too. A detector beside an open hatch reads clean air while the cabin below fills.

No CO alarm: example findings

The same defect written up at each grade, the way Axsail writes it from what the surveyor says on board. The grade follows what was found, so use these as wording, then grade what you see.

SAFETY EQUIPMENTA
Aft cabin and saloon

No carbon monoxide detector in the aft cabin or saloon. Vessel has a diesel generator and a diesel-fired cabin heater, and the aft cabin is used for sleeping.

Recommendation: Fit marine-rated CO detectors to ABYC A-24 in the aft cabin, the forward cabin and the saloon before the vessel is next used overnight.

SAFETY EQUIPMENTB
Saloon, CO detector

CO detector fitted in the saloon. Replacement date on the label has passed and the unit is a household model with no marine listing.

Recommendation: Replace with a CO detector tested to UL 2034 for recreational boats, and add detectors in each sleeping cabin, within 12 months.

SAFETY EQUIPMENTC
Forward cabin, CO detector

Marine CO detector in date and working on test. Fitted directly beside the forward hatch.

Recommendation: Move the detector away from the hatch to a spot with normal air circulation at the next maintenance period.

ASafety. Safety or compliance deficiency. Fix before the vessel is next underway.
B12 months. Deficiency that needs timely attention. Fix within about 12 months.
CRoutine. Note or observation, cosmetic or maintenance. Routine maintenance at the owner's convenience.

What the fix costs

Job Reported cost
Marine CO detector, per habitable space Detector price
Fitting, battery or 12 V Owner or electrician's time
Moving a badly placed detector Owner's time
Replacing units past their date Detector price

One of the cheapest safety findings to put right, and one where the buyer can fix it before the first night aboard.

Photos to take

Each detector with its label readable, the replacement date close up, any cabin without one, and the CO sources such as the generator and heater exhaust. With Axsail, say which cabin you're in as you take the photo and it goes on the CO finding.

Writing it up

List the habitable spaces and which have a detector, the type and replacement date of each, whether it worked on test, and the CO sources aboard. Name the standard in the recommendation: "fit CO detectors to ABYC A-24 in each habitable space".

Frequently asked

Where should a CO detector go on a boat?

ABYC A-24, in its latest revision, asks for detectors that monitor the air in every habitable space, which ABYC defines as spaces used for sleeping, cooking, eating, navigating or steering, and washing or the heads. Storage lockers, open cockpits and engine rooms don't count as habitable.

Can I use a household CO detector on a boat?

ABYC asks for detectors tested to UL 2034, including the sections for use on recreational boats. A household unit may not be built for the vibration, damp and 12 volt supply on a boat, so look for one listed for marine use.

Where shouldn't a CO detector go?

ABYC lists three things to avoid. Places where it can be damaged, places where the air is diluted, such as beside hatches, ports or ventilation openings, and dead corners with little air movement.

How often should a boat CO detector be replaced?

Before the replacement date marked on the unit. Sensors wear out, and ABYC's guidance is to replace each detector before its date.

What should I do if the CO alarm goes off?

ABYC's advice is to evacuate, ventilate, investigate and put the cause right. Don't silence it and carry on. A failing exhaust elbow, a generator running at anchor and a neighbouring boat's exhaust are all possible sources.

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Standards it's judged against

ABYC

American Boat and Yacht Council standards

What the American Boat and Yacht Council is, how its standards are written and kept up to date, why they're voluntary but still decide survey findings, how to get the full text, and the standards surveyors cite most.

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ABYC A-1

Liquefied Petroleum Gas (LPG) Systems

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ABYC A-24

Installation of Carbon Monoxide Detectors and Alarms

What the latest revision of ABYC A-24 asks of carbon monoxide detectors on boats, which spaces count as habitable, which detectors qualify, where not to fit them and how to cite A-24 in a finding.

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Fire Protection Standard for Pleasure and Commercial Motor Craft

What NFPA 302 covers on pleasure and commercial boats under 300 gross tons, fire, explosion and carbon monoxide hazards, the latest additions on lithium batteries and engine compartment detection, and when surveyors cite it.

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