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What You Can’t See Can Hurt You

Carbon monoxide-related deaths and poisonings have dropped over the last 20 years, but boaters must still be aware of the hazards

Six vessels anchoring together with numerous young adults onboard enjoying sunny weather.

Docking, anchoring, or rafting within 20 feet of boats running generators or engines increases the chances of carbon monoxide poisoning and possibly even death. Photo: Stacey Nedrow-Wigmore

Life jackets and throwable device? Of course. Visual distress signal? Roger. First-aid kit? Got it. Fire extinguishers and signaling devices? Check and check. VHF with DSC? Yup. Anchor? Affirmative. You might think these items would be enough to protect you and your crew in most boating situations. But there may be a silent and invisible killer in your midst that these items won’t help with or fix.

Carbon monoxide, or CO, is a colorless, odorless, tasteless gas produced when burning any carbon-based fuel – gasoline, diesel, propane, wood, and so on. While the most common source of CO is exhaust from gasoline or diesel engines and generators, it can be produced by any open-flame device, such as a stove, heater, or grill. When inhaled, CO displaces the oxygen in your blood and deprives your body of oxygen. Symptoms mirror those of other common issues such as seasickness, intoxication, and dehydration, so carbon monoxide poisonings are often missed until it’s too late. Breathe in enough CO and you might pass out; it can kill in just minutes.

The BoatU.S. Foundation for Boating Safety and Clean Water is an innovative leader that aims to reduce boating accidents and fatalities, increase stewardship of waterways, and keep boating a safe and enjoyable pastime. It accomplishes this with educational outreach directly to boaters through its many programs including nationwide life jacket loaner locations, on-water powerboat training, abandoned and derelict vessel removal grants, and EPIRB and PLB rentals. The Foundation is a national 501(c)(3) nonprofit organization primarily funded through grants and individual donations.

But there’s some good news

While the realities of CO are serious, there’s also some optimistic news. The most recent U.S. Coast Guard Recreational Boating Statistics report shows only six reported cases of carbon monoxide poisoning and no deaths in 2022, a sharp decline from nearly 100 fatalities and 377 nonfatal CO poisonings just two decades ago.

This drop can be correlated to several factors. First, modern boat engines have become dramatically more efficient. Fuel injection, engine-control modules, and closed-loop controls result in a more complete combustion process, which decreases CO. In addition, around 2010, gasoline inboards and sterndrives began using catalytic converters, which also aid in reducing CO.

A second reason why CO poisonings have decreased is due to a study and recall of houseboats in the early 2000s. After nine deaths and more than 100 poisonings on Lake Powell over the course of a decade, mainly attributed to poor design and lack of boater awareness to the hazards, the Coast Guard urged houseboat manufacturers to make changes to designs, especially regarding the placement of generator exhausts – moving them from the transom to the side of the hull to avoid pulling the exhaust back into the cockpit.

A third contributor to the decline can be attributed to multiple recommendations and requirements for boatbuilders, introduced by the American Boat & Yacht Council. ABYC called for the sealing of engine room bulkheads; revised requirements for exhaust locations; called for installing CO detectors; made changes to the design, construction, and testing of boats in consideration of carbon monoxide; added transom danger and helm warning labels; and, along with other organizations including the BoatU.S. Foundation, disseminated information about the hazards of CO.

Still, while CO poisonings and deaths are generally rare, it’s important for boaters to remain aware of the potential hazards and take them seriously.


Marine carbon monoxide detectors have a clearly visible “replace by” date. Check your detectors to ensure they’re functional or need to be replaced, typically every five years.
The new CO detector, CO Alert ($349) from Digital Yacht that can be plugged into a boat’s network for extra monitoring capabilities

Photo: Digital Yacht

Most modern boats are moving toward having all on-board systems interconnected and monitored from a single multifunction display or even remotely through an app — so when one unit sounds, they all do.

A new CO detector, CO Alert ($349) from Digital Yacht ( can be plugged into a boat’s NMEA2000 network for extra monitoring capabilities. In addition to producing a loud alarm from the detector itself, CO Alert’s integration produces pop-up alerts on compatible multifunction displays to alert the helmsperson. This is helpful if, for example, you’re underway and the alarm cannot be heard over engine noise. The manufacturer says it can be expanded to send text message alerts to a remote phone with additional equipment.

Instead of deriving power from its own battery, like some analog alarms, CO Alert is directly connected to the boat’s DC battery system, consuming 25 mA of current. This eliminates the potential problem of batteries corroding and failing in a marine environment. — KELSEY BONHAM

Prevent CO poisoning on boats

1. Properly install and maintain all fuel-burning engines (including generators), grills, and appliances aboard.

2. Educate passengers and crew about the dangers, signs, and symptoms of CO poisoning during your predeparture safety brief. 

3. Avoid swimming or playing near engine or generator exhaust discharges.

4. Avoid closed-off, poorly ventilated areas onboard when your engine is running, or if your dock neighbor’s engine is running, especially if the wind is blowing from astern.

5. Never ride or hang on a swim ­platform when the engine or generator is running.

6. Ensure all vents, flues, and exhaust outlets are free of obstructions such as debris, seaweed, or algae.

7. Keep at least 20 feet away from other boats running an engine or generator, especially if wind is directing their exhaust your way.

8. Avoid sitting under the dodger when motoring downwind. CO poisoning has been reported in cases where people in the cockpit breathe fumes blown into the dodger, which can trap the gas. Powerboats running with the door between the cockpit and main cabin open can also experience this due to the “station wagon” effect.

Signs & symptoms of CO poisoning

  • Headache
  • Dizziness
  • Weakness
  • Nausea
  • Vomiting
  • Chest pain
  • Confusion

If the presence of CO is suspected, open all windows, hatches, and ports to ventilate. If someone shows signs of CO poisoning, move them to fresh air and seek medical attention immediately. — S.W.

9. Following manufacturer recommendations, install and maintain a working CO detector tested to the UL 2034 standard, which is approved for marine use. (CO detectors made for home use are tested to a different standard that may not be compatible with a marine environment.) ABYC recommends that CO detectors be installed in all enclosed accommodation spaces. This is especially important for any cabins below the waterline. Choose a location that both protects the detector from physical damage (e.g., rain, spray, sunlight) and avoids what ABYC calls “dilution of sampled air” that could occur near hatches, ports, or forced ventilation openings. Locations containing “dead air” spaces (such as corners) should be avoided as well to prevent distorted readings.

10. Never disconnect a CO detector because of nuisance alarms. Take all alarms seriously. If you hear a “chirp” from a hidden place, look for a weak battery in a CO detector or component.

11. Don’t run the generator while you’re sleeping, even to power the air-conditioner. As many boaters use generators to power air conditioners and other appliances (particularly while at anchor), a better option is to install a CO alarm system designed to shut off the generator once CO is detected. One example is those offered by Fireboy-Xintex.

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Stacey Nedrow-Wigmore

Managing Editor, BoatUS Magazine

Stacey is an award-winning marine journalist and photographer who, as BoatUS Magazine's managing editor, handles some of the national publication’s most complex features, as well as keeping it on time, accurate, clear, and timely. Stacey also manages the magazine’s active website and social-media engagement, and is part of the BoatUS video team, helping to produce more than 30 how-to videos a year. Stacey recalls that one of her earliest memories in life includes being hung by her ankles in the engine compartment of her family's 1963 Egg Harbor, helping with repair work and searching for lost items. Her love of boats may only be matched by her love of horses; she spent 20 years writing, editing, and photographing for equestrian magazines and books — including Practical Horseman