BOAT-COMPARATOR Guide

Carbon Monoxide Poisoning on a Rental Boat: An Invisible Risk Worth Knowing

Generators, inboard engines, swim platforms: carbon monoxide kills recreational boaters every year without a smell or visible smoke. How to recognise the danger and protect yourself on a rental boat.

Carbon monoxide (CO) is invisible, odourless, and still responsible for occasional fatal poisonings on rental boats every year, mostly around generators and poorly ventilated inboard engines. It is a real risk, but a very simple one to prevent once you know where it hides.

Where CO comes from on board

CO forms in the exhaust of any combustion engine: an inboard engine, an onboard generator, but also a barbecue or stove used in a poorly ventilated space. On a boat, it collects especially near the swim platform and the stern, behind a boat at anchor or at the dock with the engine running, and below deck or in the cabin if an air intake pulls in exhaust from a boat moored close alongside.

The situations that expose people most

Two scenarios come up repeatedly in the US research on the topic. The first is swimming or "teak surfing" (being towed or swimming just behind the stern while the engine idles): a study published in the American CDC's epidemiological bulletin documented children poisoned by CO while swimming or being towed right behind a running motorboat (CDC, Morbidity and Mortality Weekly Report, 2002). The second involves cabin cruisers or houseboats moored with the generator running: a CDC investigation into poisonings on Lake Powell (Arizona/Utah) recorded several deaths among swimmers gathered under a houseboat's swim platform while its generator ran, alongside roughly a hundred non-fatal poisonings recorded over a decade on that single lake (CDC, Lake Powell houseboat report, 2000).

Signs that should raise a flag

Headache, dizziness, nausea, unusual drowsiness: the early symptoms of CO poisoning are easy to mistake for seasickness or heat exhaustion, which often delays diagnosis on board. The key tell: several people are affected at once, usually near the stern or in the cabin, and symptoms ease as soon as they move into open air toward the bow.

Good habits on a rental boat

Never swim, and never let a child swim, near the swim platform or a running exhaust, even at anchor. Ventilate the cabin thoroughly before sleeping or spending time in it, especially at anchor between two boats rafted together. During the technical briefing before departure, ask about a CO detector on any closed-cabin model fitted with a generator or a combustion heater — increasingly common on newer charter fleets, notably in Croatia and Greece. If in doubt, cut the engine, get into open air, and ventilate before anything else.

Keeping the risk in perspective

On an open, well-ventilated RIB or day cruiser, the risk stays very low: nearly every documented case involves an enclosed space (a closed cabin, a generator, prolonged teak surfing). The point is not to give up swimming off the stern — it is to keep one simple habit: engine off before anyone swims behind the boat, cabin ventilated before anyone sleeps in it. The rest of the mandatory safety equipment aboard rounds out these habits before heading out.

Compare the platforms now →

Also worth reading

• How much does it cost to rent a boat in 2026? Real prices
• License-Free Boat Rental in France: Rules, Prices & Where to Book
• Renting with or without a skipper: how to choose