Diesel exhaust

Does it smell like exhaust fumes or raw fuel ?

In a 30 year old boat the smell of diesel could be coming through the old hoses, but check for actual leaks or evidence of past leaks. Used to run a boat that fumes came into the stateroom from the line form the fuel neck when the tanks were too full The smell of exhaust is of more concern, and can kill you. Check your exhaust system for tell-tales of leaks (most likely around connections). If you have engine room blowers they may be drawing the exhaust fumes in when stopped. Yes a gas detector is useful, and pretty much necessary to locate the source, but I'm not sure of the type you need. Fire Departments have them. Maybe if a member works for a FD they can give some insight, otherwise a call to the local FD may be a good idea when you smell it.

The OP has a diesel boat given what he says its powered by. I am not aware of anyone who has been overcome by CO produced by a diesel engine.

Also, I have been in a few engine rooms where the fumes were strong enough to make my eyes water and am still here.

Any combustion engine fueled by a hydrocarbon based fuel produces carbon monoxide, (CO), which is preferentially absorbed as compared to oxygen by human's red blood cells as they flow thru lung tissues. Under no circumstances should diesel engine exhaust be considered benign, or less dangerous to humans safety than engine exhaust produced by alternative fuels such as gasoline, which is a hydrocarbon fuel, as is diesel.

Is this a boat you just purchased or one you've owned for a while? To your knowledge, how long has this problem existed?

Seems likely if you didn't notice it when purchasing and the surveyor did not comment on it that it worsened with use, which certainly leads to the theory of it being an abnormal leak, whether fuel or exhaust, and not a normal characteristic of the boat. One of the yards in your area may well have leak detection equipment. That would be ideal.

Is there any liquid in the bilge (s) ?

High humidity can magnify smells which might account for the above.
If there are no wet spots on the engines genny, no puddles anywhere, then maybe the soot is the issue. Take a sniff of some raw fuel and see if that's the same smell. At least that might narrow down the search.

Can you start the engines and observe ? Maybe there is an exhaust leak that might be more evident when they are cold ? Does it even get cold in Corpus Christi ?

While the above advice is not wrong or harmful, a healthy dose of reality should also be applied.

"Lastly, an extensive literature review produced no scientifically reported cases of fatal CO poisoning attributed to diesel fuel exhaust."
http://www.ncbi.nlm.nih.gov/pubmed/18643868

Carbon monoxide poisoning is probably among the least of the hazards of a diesel exhaust leak and the least threat to people on the boat. The other nasty stuff in diesel exhaust has a well documented history or causing health problems and that should be the driving force behind finding and eliminating exhaust leaks.

Installing an ultra sensitive CO detector in the area(s) of the strongest smell might be a good way to determine if the source of smell is an exhaust or a fuel issue.

Marmot: Your citation is without credibility, as history has demonstrated since its invention more than
one-hundred-twenty years ago. During World War II the Nazis employed it as a means of effecting human homicide. The remainder of your post is misleading, and tacitly encourages a reader to minimize or disregard the fact that any combustion engine utilizing diesel fuel produces carbon monoxide (CO), which is preferentially absorbed by the human body as compared to oxygen, and is cumulative over time. This is why seemingly minute concentrations of CO are potentially hazardous.

Regarding the recommendation to install a CO detector as a means of distinguishing between exhaust or diesel fuel as the source of smell, note that carbon monoxide is an odorless substance to humans, thus by definition it is not the cause of smell, although other chemicals contained in diesel engine exhaust gases might be detectable by smell, however not by a CO detector. Also, liquid or vaporized diesel fuel by definition does not contain CO, thus a CO detector is irrelevant to discerning presence, or absence of diesel fuel in any form.

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