What is the effect of idling a vessel at slow speed?

Idling a vessel at slow speed can indeed lead to carbon monoxide accumulation inside the boat. When a vessel's engine runs at low RPMs, it may not create sufficient exhaust flow to effectively disperse harmful gases, such as carbon monoxide. This gas can build up in enclosed spaces and pose serious health risks to anyone onboard.

Understanding the implications of idling is crucial for safe boating practices. Engine efficiency, fuel consumption, and vessel movement are also important considerations when operating a boat, but they are secondary to the critical concern of ensuring that harmful gases are properly vented away from passengers and crew.