Carbon Monoxide Outside the Boat: Teak Surfing, Swim Platforms, Generators and Raft-Ups

Walk around the boat and find every place exhaust comes out: outboard (through the prop hub and the idle relief port on the leg), sterndrive or inboard (through the prop or transom outlets), and the generator exhaust (often on the side or transom). The Coast Guard's first rule is to know where they are and keep everyone away. Point them out to your regular crew.

The Coast Guard lists these spots and situations:

• The swim platform and back deck while engines or a generator run.
• Under the swim platform or swim deck, where exhaust outlets are. The Coast Guard says never go there unless the area has been properly ventilated.
• Canvas enclosures that don't vent well.
• Blocked exhaust outlets, such as a boat nosed against a seawall or another boat.
• Another vessel's exhaust: CO from the boat docked next to you can be just as deadly.
• The "station wagon effect" (back-drafting): moving forward, the boat drags a low-pressure pocket behind it that pulls exhaust back into the cockpit. Connecticut's boating agency describes the same suction trapping fumes behind the boat.
• Slow speed, idling, or stopped. CO can stay at dangerous levels even after the engine is off.

"Teak surfing" or "platform dragging" means holding onto the swim platform or transom of a moving boat and riding its wake, often without a life jacket. The Coast Guard is blunt: teak surfing is NEVER a safe activity. The swimmer's face is right in the exhaust pocket, a few feet from the propeller, and if they pass out they sink.

Body surfing directly in the wake behind a moving boat has the same problem. Wakesurfing on a proper surf boat, with the rider on a board well behind the boat, is a different activity with its own rules; see our wakesurf guide.

Several states have made teak surfing illegal, and some go further. Washington's law (RCW 79A.60.660, the Jenda Jones and Denise Colbert Safe Boating Act of 2006) is a good example of how these laws read:

• No one may operate a boat, or even let the engine idle, while someone is teak surfing, platform dragging or bodysurfing behind it.
• No one may operate a boat or let the engine idle while someone occupies or holds onto the swim platform, swim deck, swim step or swim ladder.
• Brief exceptions: helping dock or depart, getting on or off the boat, and law enforcement or rescue.
• Fine up to $100.

California's law (Harbors and Navigation Code 681) reads almost the same: it's unlawful to operate a motorized boat or let its engine idle while someone is teak surfing, platform dragging or bodysurfing behind it, or while someone occupies or holds onto the swim platform, deck, step or ladder, with the same brief exceptions for docking, boarding and rescue. It defines teak surfing as holding onto the platform, ladder or any part of the outside of the transom while the boat is underway at any speed, so a slow idle through a no-wake zone counts.

California also requires two CO warning stickers when a new or used motorized boat is sold there (Harbors and Navigation Code 683): a small one inside where the operator sees it right away, and a larger one facing out on the stern or transom. A dealer must put them on before the sale is complete; in a private sale, the DMV includes them with the new owner's registration papers and the owner must put them on. If you bought a boat in California and the stickers are missing or faded, ask your state boating agency (the Division of Boating and Waterways) about replacements. Other states have similar rules. Check your state boating agency's handbook before the season. Even where it's legal, it isn't safe.

Make it a house rule: nobody sits on, stands on, or hangs from the swim platform or ladder while an engine or generator is running. That includes:

• Kids dangling feet off the platform while you idle into a cove
• Swimmers waiting on the ladder while the skipper "just repositions"
• Someone holding the boat off at the dock from the platform

Turn the engine off before anyone uses the ladder, and keep the key out until everyone is back aboard and accounted for. That also protects them from the propeller.

The Lake Powell deaths were mostly tied to generators running for air conditioning or TV while people swam at the stern. If anyone is in the water, on the swim platform, or near the stern, turn the generator off. Remember the Coast Guard's warning that CO can linger after shutdown: give the area time to air out before anyone swims near the outlet, and never let anyone swim under a swim deck or into the space beneath the stern. The Coast Guard also says to run exhaust blowers whenever the generator is operating.

When boats tie up together or anchor close:

• The Coast Guard's trip checklist says to be aware of exhaust from boats you're docked or rafted with.
• Agree as a group: no engines or generators running while people swim among the boats. If one boat must run a generator, it goes on the outside end, downwind.
• Keep swimmers and floats away from every boat's stern, not just yours.
• A neighbor idling to recharge batteries can fill your cockpit with exhaust; ask them to stop or move.

• Running slowly with the stern canvas or enclosure closed is the classic setup. Open the forward panels or hatches so fresh air flows through.
• Don't idle for long periods in one spot, especially in calm air.
• If you smell exhaust in the cockpit, change speed or heading, open up the canvas, and get people forward.
• Tie-ups against a seawall or another boat's hull can block your exhaust; don't run engines for long there.

A leaking exhaust puts CO where it shouldn't be. The Coast Guard's checklists:

• Each trip: confirm water comes out of the exhaust when the engines and generator start, and listen for a change in exhaust sound.
• Monthly: check exhaust clamps, look for rust or black streaks, water leaks, and cracked fittings; check rubber exhaust hoses for burned, cracked or stiff sections.
• Yearly, by a qualified technician: replace bad hoses, inspect manifolds, risers and elbows, check the water pump impeller, and clean the generator's anti-siphon valve if it has one.

Our exhaust riser and elbow guides cover what to look for.

Treat any seasick-looking symptoms near the stern as possible CO poisoning, as the Coast Guard advises. Its emergency steps:

1. Move the person to fresh air, and keep rescuers safe; the area may still be full of CO.
2. Shut off the engines and generator.
3. Give oxygen if you have it.
4. Call for medical help (911, or VHF 16 offshore). If they aren't breathing, start rescue breathing or CPR.

The CDC adds that people who have been drinking or are asleep can die before they ever notice symptoms.

• A simple sign or label on the transom ("Engine off before using the swim platform") works well.
• Add "stay off the swim platform when engines run" to your pre-departure briefing (see our briefing guide).
• On houseboats and rentals, ask where the generator exhaust is before you swim.
• Install CO alarms in any cabin and test them each trip, as the Coast Guard's checklist recommends. They won't protect people outside, but they protect sleepers inside.