Ever since the late 1990s when a rash of fatalities aboard houseboats underscored the dangers of carbon monoxide poisoning, the marine industry and the U.S. Coast Guard have been trying to figure out how to minimize or eliminate infiltration of this dangerous exhaust byproduct into the living spaces of recreational boats.

Sources of carbon monoxide (CO) on boats include gasoline engines and generators, cooking ranges, and space and water heaters. The tasteless, odorless, colorless gas, produced any time a material containing carbon — such as gasoline, wood, propane, coal or natural gas — is burned, is called “the silent killer” for good reason. Exposure to prolonged or high concentrations of CO can result in death or serious injury because CO reacts with hemoglobin and reduces blood’s oxygen-carrying capacity. Symptoms mimic sea sickness.

Today, more boatbuilders are installing carbon monoxide detectors as standard equipment and boat owners are more aware of CO’s risks.

Still, the recent recall of certain sport cruisers, the firsthand report of a boat owner and an ongoing study by the U.S. Coast Guard all demonstrate that the risk of CO poisoning remains because the problem defies a simple solution.

Instant Recall
High levels of CO at the helm stations and cockpits of 47 and 37 Excalibur express cruisers sold by Wellcraft and Four Winns prompted their Australian builder, The Riviera Group, to initiate a recall campaign in late 2005.

Although Riviera’s report to the Coast Guard states that no accidents or fatalities have occurred, federal law requires that boatbuilders recall vessels when they contain defects that “create a substantial risk of personal injury.”

According to a report by a Riviera spokesman,“ After the design and building of our new M360and M400 Sport Cruisers, we tested these products extensively for CO levels.

“What we found were levels of CO that exceeded the American Boat & Yacht Council (ABYC) guidelines in the cockpit and helm station areas. It is important to note that the ABYC guidelines seem to say that ventilation is the only solution; we disagree and have gone much further in developing other modifications to the boats to reduce CO levels,” said Riviera.

Riviera called in an aerodynamicist from the Australian GMH race car team to help with a re-design of the boats’ hardtops to eliminate backdrafting, also known as the “station wagon” effect.

Air moving over or around a boat creates a low pressure or suction area around the stern that can increase the CO level on the boat, according to ABYC. “Under certain speed and operating conditions, the low pressure area may form in other regions and permit carbon monoxide to enter the hull through openings that are not on the back of the boat.” These openings could include vents for air conditioning, the head and galley, as well as port lights, hatches, doors and cockpit and deck drains.

Riviera also determined that the design of the exhaust bellows used on the MerCruiser MX6.2 320HP, 496 MAG and 496 MAG HO engines with which the boats were equipped was also contributing to carbon monoxide build-up. “Once the testing was complete we liaised with Mercury in Stillwater, OK, who approved the fitting of enclosed exhaust bellows,” according to Riviera.

The last component of the recall requires boat owners to take specific measures to decrease risk.

Riviera says, “Ventilation of the cockpit is still paramount.” To this end, a recalled boat will receive a decal warning of the need to keep forward-facing port lights or windows open when vessels are underway, particularly at speeds below 10 knots or when anchored, docked or rafted with other vessels. Boat operators need to make sure that the cockpit is well ventilated at all times when engines and generators are running because CO can migrate from there into enclosed cabin spaces.

Concerned Owner
The owner of a 2004 Brunswick-built Meridian 381 Sedan Flybridge reported to BoatU.S. that he’s been unable to use the boat due to high concentrations of CO — in excess of 1,000 ppm, high enough to cause permanent brain damage or death in less than an hour — in the main cabin. The problem has been present since the day he took delivery, regardless of whether the boat is in the slip, underway or at anchor.

Although the “new boat smell” that comes from plastic resins, veneers and upholstery can sometimes trip CO detectors, the owner says that the detectors on his boat sound only when the twin MerCruiser 8.1L engines and the generator are running. Factory technicians have attempted without success to locate the source of the fumes. The manufacturer continues to test and make repairs. The owner is considering litigation since his requests for a replacement boat have been denied.

A spokesman for Meridian told BoatU.S. that the only issues they’ve had with CO detectors occur when boat batteries drop below 12 volts. He said they had problems with the “station wagon effect” on the Meridian 580 model until the exhaust was routed underwater. He also said that a design change for the 2006 391 (the 381 will be discontinued) also routes the exhaust underwater.

The Coast Guard’s Role
According to U.S. Coast Guard accident statistics, nearly 200 fatal CO poisonings are known to have occurred on or near recreational boats over the years. Since the symptoms from exposure to low levels are similar to seasickness, the actual number of boaters who have been affected by CO may be considerably higher than statistics indicate.

For the past year, the Coast Guard and ABYC have been testing express cruisers to “provide a better understanding of the CO exposures that occur, to identify the most hazardous conditions and to begin the process of identifying controls to prevent or reduce CO exposures,” says Dan McCormick of the Coast Guard’s Office of Boating Safety. The tests follow guidelines set up by the National Institute for Occupational Safety and Health. NIOSH, which is part of the Centers for Disease Control and became involved in the boating CO issue following the houseboat deaths.

“A great deal of work has already been performed to evaluate CO exposures and controls on houseboats, but less effort has been given to understanding the extent of the CO hazard on other types of recreational boats,” McCormick said.

According to ABYC, “Carbon monoxide accumulation is affected by a multitude of variables: boat geometry, hatch, window and door openings, ventilation openings, proximity to other structures (like docks and neighboring boats), swim platforms, canvas enclosures, location of exhaust outlets, vessel attitude, wind direction, boat speed and boat system maintenance.”

Ten different models of boats built by five different manufacturers were evaluated while stationary and at various speeds from 5 to 25 mph. Each test boat was fitted out with multiple sensors so that CO concentrations could be measured at various places on board and with canopy enclosures set up in different configurations. Results of the study are under review and should be published within a few months.

Safety Awareness
To avoid CO dangers, the Coast Guard recommends:

(c) Copyright BoatU.S. Magazine, July 2006