You only need carbon monoxide detectors In the enclosed cabin, right? - Wrong! By Thomas C. Benton, AMS®, CMS, CMI
Sometimes a flybridge or cockpit can accumulate dangerous levels of carbon monoxide (CO)
from Back drafting, also known as the "Station Wagon" effect. This can happen even if the
cockpit doesn't have a full enclosure.
Recently while assisting a major manufacturer with endurance testing on a pair of new 7.4 Liter EFI gasoline inboard packages, I noticed that spray from behind the boat was hitting me on the back of my neck as I ran down the lake. The test platform that had been chosen for the new package is a typical 30' express cruiser. We needed to be able to run in any weather conditions, so we had installed a partial top from the Radar arch to the windshield. With cold weather being just around the corner, we planned to install side curtains and an aft curtain to make the 300 hours of full throttle testing bearable.
After just a few days of operation, I was starting to develop headaches. At first I thought that the constant grueling operation at 4400 RPM, and the noise were to blame. Then it became apparent to me that since the spray was coming from behind, the exhaust fumes that exit the stern below the swim platform, must be coming into the cockpit as well. I thought that surely without the side and aft curtains installed, I must be getting enough fresh air, and when we installed the aft curtain, the problem should stop. We installed the side curtains, and the spray seemed to get worse. After a couple of days, we installed a modified aft curtain on the back side of the radar arch. This stopped the spray from entering the cockpit, however the headaches didn't go away. By this time I was even more suspicious about the cause of my headaches, so in an effort to confirm my suspicions, I decided to install a CO detector.
I ordered some inexpensive carbon monoxide indicating devices, and installed one on the dash. These "buttons" as I will call them, are marketed by Applied Science Corporation, Tampa, Florida. They are available from the BOAT/US catalog for $3.22 each, postage paid. They are orange in color, and turn darker as CO levels increase. It takes from one to six minutes for the device to change color, depending on the concentration of CO that it is exposed to, and when exposed to fresh air for a period of time, it turns back to orange.
Over the next few days, I watched as the button seemed to change from orange to light or medium gray, but I wasn't sure if it was reacting to CO, or if the overcast weather was playing tricks on my eyes. The units come sealed in plastic, and are reported to be effective for one month after opening, so I placed a sealed one next to the open one for color comparison. Sure enough, even with the aft curtain installed, it appeared that some carbon monoxide was still getting into the enclosure. During a morning engine warm up, while the boat was tied up in the covered slip, the button turned almost black. This time I could even smell the exhaust, and I decided that the button did in fact work, and that the vessel did have a CO problem.
I started looking for the point of CO intrusion. The zippered entrance in the aft curtain leading into the enclosed cockpit was at times puckered inward at the bottom, depending on the boats direction and speed in relation to the wind. I found that unzipping the side curtains would change the amount of pucker, but didn't do away with it. I tried opening the forward facing cabin hatches about 1/2", this seemed to create a positive pressure in the enclosure, and doing so caused the bottom of the aft curtain to pucker outward instead of inward. After running this way for an hour or so, the button had changed back to orange, and after a day of running with positive enclosure
pressure, I wasn't having headaches anymore.
The buttons do not meet the recommendations of the American Boat and Yacht Council for "Carbon Monoxide Detection Systems On Boats", but they helped me prove to myself, and an associate, that the problem did exist, and may well have saved my derriere. Once the problem had been identified, a permanent CO detector with three levels of protection was ordered for installation in the cockpit area. The modified canvas enclosure that we installed on this boat, and the fact that we are operating at approximately 40 mph for extended periods of time, may be contributing factors to the Back drafting problem. However, it is my opinion that any "Express Style" cruiser with exhaust exiting the stern, may be subject to the same problems.
If you read any of the multitude of boating magazines and industry newsletters, I'm sure that you have noticed an increase in articles on carbon monoxide lately. After attending an ABYC seminar on accident investigation last year, and sitting in on the excellent presentation that Charlie Game put on concerning carbon monoxide testing on Hatteras Yachts, I started including a general recommendation in all of my surveys, suggesting that a CO detector be installed in the enclosed accommodation spaces, or sleeping quarters, aboard the marine vessel. My recommendation will now be modified to include consideration of the cockpit, and flybridge areas as well, especially if the vessels design, and canvas configuration, lends itself to Back drafting, or the "Station Wagon" effect.
Even with detectors aboard, everyone should be able to recognize the symptoms of CO poisoning. I got headaches, but victim's can also experience nausea and even dizziness initially. The symptoms are often confused with seasickness. The effects of CO are cumulative, and only when levels of CO have become critical will unusual symptoms appear - The victim's lips may turn bright red and he or she may lapse into convulsions.
Tom Benton, AMS
Marine Surveyor & Consultant
I have determined that it is prudent to install a carbon monoxide detector in any enclosed space that is inhabited aboard a marine vessel.
Office: (918) 782-1001, - Fax: (918) 782-1004