Carbon monoxide (CO) is an insidious threat on the water, a colorless, odorless, and tasteless gas that can poison without any immediate warning. Produced by the incomplete burning of carbon-based fuels, CO is a common byproduct of marine engines and appliances. The environment of a boat presents unique and heightened exposure risks compared to land, allowing this gas to accumulate rapidly in concentrations that are immediately dangerous to life. Understanding how this poison is created and trapped is the first step in protecting yourself and others.
Sources of Carbon Monoxide on Watercraft
The presence of combustion engines is the primary source of carbon monoxide on nearly every boat. Propulsion engines, whether inboard or outboard, continuously expel exhaust containing CO as a result of burning gasoline, diesel, or propane. This production occurs even when the engine is well-maintained and running smoothly, underscoring that all engine exhaust is a source of risk. Auxiliary equipment like onboard generators are also significant contributors, especially on larger vessels. Fuel-burning appliances, such as galley stoves, water heaters, and space heaters, add to the overall CO load, particularly if used in poorly ventilated areas.
Unique Accumulation Zones and Exposure Risks
The danger of carbon monoxide on a boat lies in the specific physics of how it becomes trapped and concentrated on the water. A phenomenon known as the “station wagon effect,” or back drafting, occurs when the boat is underway. This creates a low-pressure vacuum at the stern that actively pulls exhaust fumes back into the cockpit and cabin areas. This effect is magnified when traveling at slow speeds, idling, or when the boat is improperly loaded, causing a high bow angle.
High-Risk Stern Zones
The area around the stern, including the swim platform, is the most hazardous zone on any boat. Since engine and generator exhaust outlets are located here, this area becomes a high-concentration pocket of CO, especially when the boat is idling or moored. Activities like “teak surfing” or sitting on the swim platform while the engine is running place a person directly in the path of potentially lethal fumes. Furthermore, when anchored, exhaust from a nearby vessel’s running engine or generator can easily drift into the cabin and cockpit of an adjacent boat.
The Physiological Mechanism of CO Poisoning
Carbon monoxide is toxic because of its strong chemical affinity for the oxygen-carrying molecule in red blood cells, hemoglobin. CO binds to hemoglobin approximately 200 to 250 times more readily than oxygen does, forming a compound called carboxyhemoglobin. When CO molecules occupy the binding sites on hemoglobin, they effectively displace oxygen, severely reducing the blood’s capacity to transport oxygen throughout the body. This displacement leads to cellular hypoxia, or oxygen deprivation, which primarily affects the brain and the heart. Furthermore, CO binding increases the affinity of the remaining hemoglobin sites for oxygen, meaning the small amount of oxygen still bound is less likely to be released to the tissues. This two-pronged attack on oxygen delivery can cause rapid cell death and organ damage.
Recognizing and Preventing CO Emergencies
The symptoms of carbon monoxide poisoning are often subtle and easily confused with common boating ailments like seasickness or fatigue. Early symptoms include a dull headache, dizziness, weakness, and nausea. As exposure continues, these progress to confusion, vomiting, chest pain, and a rapid heart rate. A person who is sleeping or intoxicated may quickly succumb to poisoning before noticing any symptoms. If exposure is suspected, immediately move the affected person to fresh air away from the boat and contact emergency medical services.
Prevention Strategies
The most effective preventative measure is the installation and regular testing of marine-specific carbon monoxide detectors in all enclosed areas. Prevention also relies on operational awareness and maintenance:
- Ensure all fuel-burning devices are properly installed and routinely inspected for exhaust leaks.
- Use forced-air ventilation systems to maintain a constant supply of fresh air to cabins.
- Never block exhaust outlets.
- Limit idling time and avoid traveling at slow speeds for long periods.
- Keep a distance of at least 20 feet from other boats running engines or generators when anchored.
- Keep swimmers and passengers away from the stern and swim platform when the engine or generator is running.