This is an excerpt from the Compass, September of 2012, United States Power Squadrons
You see them every day: swimmers holding onto the swim platform chatting with friends onboard, boats anchored close together with air conditioners chugging away, children teak surfing off the swim platform of the family boat. All of these situations could become fatal because of the high risk of carbon monoxide poisoning. (Teak surfing is when a swimmer hangs on to the swim platform and is dragged behind the boat.)
Produced by the burning of carbon-based fuels, deadly, invisible carbon monoxide gas has no taste or smell.
Carbon monoxide from the exhaust of inboard engines, outboard engines and generators can build up inside and outside boats in areas near exhaust vents, such as the swim platform, making it dangerous to congregate or swim in these areas when the motor or generator is running.
Read more from the U.S. Coast Guard about how to protect against carbon monoxide poisoning.