I have no evidence to support this, but it's my opinion that if the smell of a fart under water will come up with the bubbles, so will the CO gas in exhaust. And it doesn't matter where else the exhausts exits, if there's no wind to blow the CO away, it can find its way into your boat. Our Party Cruiser has a dry side-exhausted Onan genny, our SkipperLiner has an under-deck wet exhaust. Both have succeeded in setting of CO alarms on calm days. And fwiw, our under-deck exhaust was tested and found to be no more less dangerous than any other type of exhaust. Several times while on the hook we've had the genny running the entire day to keep the AC and fridges running, with no signs of CO at all. BUT, there's always at least a slight breeze, and that seems to be all that's needed to disperse the C0.
You simply have to be extremely careful running the generator. If it's setting off C0 alarms, you shouldn't be running it...
Many boaters bring exhaut problems on them selves. In the south many boaters run ther Gennys 100% including me. When we anchor out we DON'T EVER use a stern anchor. Usually there is a breeze and allowing the boat to swing with the wind causes the fumes to blow away from the boat. If we leave the back doors open (not very often due to the air conditioning) we leave the front open to allow air flow thru the cabin.
If we beach we don't run the Genny unless the wind is offshore. We almost NEVER beach cause bottom jobs are so EXPENSIVE.
i start my generator before i start my main engines. when we anchor out i do turn it off for a while now and then but in mostly stays on. i have been thinking about a 1000cc honda gen for the fridge only since i dont have an inverter and dont plan on putting one in.
I know some houseboaters do that, to save gas vs running the main genset. I have a 1000... which is one of the reasons I went to solar. Listening to that thing surge every time the fridge or the battery charger kicked in was a real distraction.
Reality Check: In the south many of us run our Genny's 100%. For the most part we don't end up dead or even sick. We don't swim under solid swim platforms. Most of us pay attention to which way the breeze is blowing and keep the back shut when underway. Alternativly we crack a window in front if the back door is open. Many of us run the air conditioner at night, we keep the back door closed and anchor with a lot of scope so the boat can swing with the breeze. We keep the battries up in both CO detectors and test them once in awhile. We even inspect the exhaust system on our Genneys. (How about that) S**t can happen but most of the time, if common sense is used, we don't make the evening news.