It’s that time of year again. This past weekend, I put the canvas on my boat – always a bit of a sad day for me. It marks the end of the traditional boating season.

We’re lucky, though. Living here, we still get those occasional warm winter days that make for perfect surprise outings on the lake. Even when it’s only 50 degrees outside, the greenhouse effect inside the enclosure can make it feel like a comfortable 70 degrees on deck. Sometimes even warmer.

But there’s one thing you have to be careful about. These enclosures can trap exhaust fumes from the boat’s engine or generator. It’s a phenomenon often called the “station wagon effect” or “backdraft effect.” When a boat is moving, or when the wind blows from the stern, a low-pressure zone can form behind it, drawing exhaust fumes back into the cockpit or cabin, including under a canvas top.

These fumes contain carbon monoxide (CO), which is extremely dangerous. CO exposure can cause dizziness, nausea, confusion, loss of consciousness, brain damage, and even death.

Whether this becomes an issue depends on your boat’s design, where the exhaust exits, and even your cruising speed. It’s entirely possible that you’ll have no problem at 3 knots but start pulling fumes into the enclosure at 7 knots. Wind direction and temperature can make a difference too. The point is, don’t assume it can’t happen to you or that running at a certain speed makes you safe.

So what can you do? Here are a few simple steps to stay safe while cruising through the cooler months:

  • Install and maintain a carbon monoxide detector. If your boat has an enclosed cabin or living space, this is a must. Year-round. CO detectors save lives. Test them regularly and replace them as needed.
  • Keep fresh air flowing. Make sure there’s always ventilation when an engine or generator is running. Open a forward hatch or port to bring in fresh air, whether you’re underway or at anchor.
  • Maintain the exhaust system. Check for and repair any leaks. A small exhaust leak can quickly turn into a big problem in an enclosed area.
  • Pay attention to symptoms. If anyone on board feels dizzy, sleepy, nauseous, or develops a headache, get them fresh air immediately. Carbon monoxide is odorless, but your body will give you warning signs. Don’t ignore them.

Being able to take your boat out for a winter cruise is a real blessing — something many boaters up north don’t get to enjoy. Just make sure you take the right precautions so you and your crew stay safe and make it to next season ready for more adventures.