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Old 01-31-2023, 04:31 PM   #1
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CO danger in aft cockpit while underway

Oh knowledgeable hive...talk to me about being in the aft cockpit while underway and whether there's a significant danger of CO poisoning due to the low pressure area. Also, can you have the aft sliding doors open when underway if the exhaust ports are in the rear under the swim platform? Do all the windows/doors have to be open to push the exhaust aft? We're on Kha Shing 40 sedan. We're new to trawlers and will be taking off on the upper portion of the Loop in April.
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Old 01-31-2023, 04:46 PM   #2
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Is the boat diesel or gas powered? If it is diesel then most likely not an issue since diesels donít make much CO. Diesels do have an exhaust smell that my wife hates but it isnít CO usually. If it is gas powered very likely it will be an issue. With gas engines the station wagon effect is very common. You can try opening a forward facing hatch to try and break the low pressure area. Certainly have good quality CO detectors in the boat and when they go off immediately take corrective actions. It can be a killer.
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Old 01-31-2023, 05:07 PM   #3
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Also common on gas powered boats with a flybridge, when running downwind. A friend had that happen on his Bertram, fortunately he was a safety engineer with the local gas company and recognized the effects coming on before damage was done. He'd seen enough people who had died from it to know. He installed a CO detector on the bridge after that, already had them in the cabin.
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Old 01-31-2023, 05:11 PM   #4
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I keep saloon doors closed under way. Several CO detectors, but donít risk it.
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Old 01-31-2023, 06:54 PM   #5
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+1 to all the above. The "station wagon effect" is important to keep in mind especially with gas engines. https://grandlakeliving.com/boating-...-co-poisoning/.

We have diesel but I keep the cockpit door closed as much as possible and ventilate other areas well when it is open. And multiple types and locations for CO detectors.
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Old 01-31-2023, 07:13 PM   #6
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I know C.O. is an odorless, colorless gas and a diesel engine does not make much of it but.. If you smell exhaust there is danger..

We have a couple C.O. detectors on board, doesn't hurt anyting


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Old 01-31-2023, 07:15 PM   #7
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I keep saloon doors closed under way. Several CO detectors, but donít risk it.
Shipwright told me that also helps save headliners from premature death.
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Old 01-31-2023, 08:27 PM   #8
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I am safety oriented........ must have something to do with my career and training
Why risk CO poisoning. It can be deadly, and often victims don't even notice they are slowly being "gassed"!! It binds to human hemoglobulin better than O2 and does not dissipate easily once in the bloodstream, hence effective onboard treatment can be less than effective and/or take a long time (for symptoms to relieve).

Good advice from the others in my opinion...... keep the rear openings closed and also install CO detectors. We had side Pilothouse doors in our Nordic, and we often had them open while underway. This provided a pretty good cross draft, we never smelt diesel exhaust, and the CO alarms never went off. We always kept the rear windows and rear door closed when underway or even with the engine running.

CO is not something to take lightly (not saying you are, just advising).
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Old 01-31-2023, 08:47 PM   #9
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Diesel engine CO is quite low in the exhaust due to the high volume of air pumped through a diesel vs gas engine. Diesels have been used safely in underground mines for a very long time but do require Drager testing and good ventilation in these reasonably closed conditions.

CO from diesel exhaust in an open cockpit should be of no concern but the smell in some cases is bothersome..

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Old 01-31-2023, 08:54 PM   #10
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On some boats station wagon effect issues are speed dependent. On our boat we have to be aware of ventilation to avoid station wagon on the aft cabin deck if we're running on plane. More so with a headwind as the higher wind speed creates more suction. A tailwind or crosswind that's on or behind the beam fixes it. And when running at slow cruise it's a total non issue unless the wind is just right to push fumes onto the boat (only had it happen once and a 20 degree course change and slight speed reduction solved it).
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Old 01-31-2023, 09:11 PM   #11
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Our last boat, a sundeck, would get exhaust fumes inside if the wind was from astern because we cruised at 9 knots. If we changed direction usually it would go away. My wife has the most sensitive nose on the planetÖ
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Old 01-31-2023, 09:19 PM   #12
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I assume this also means no guests sitting in the aft cockpit underway?
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Old 01-31-2023, 09:26 PM   #13
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Our last boat, a sundeck, would get exhaust fumes inside if the wind was from astern because we cruised at 9 knots. If we changed direction usually it would go away. My wife has the most sensitive nose on the planetÖ
Interestingly we've only had that issue once at slow cruise (6.5-7 kts for us). Most of the time that fumes stay low enough to the water that they blow around us rather than blowing up onto the boat (and potentially in). The one time it happened the wind was moving only a half knot faster than us, so the fumes were rising more before getting blown past us. Slowing down a knot and taking a slight angle to the wind fixed it.
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Old 01-31-2023, 09:57 PM   #14
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I assume this also means no guests sitting in the aft cockpit underway?
And not the only reason. If you can't see them back there they could fall overboard and you'd wouldn't know it for miles.
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Old 02-01-2023, 09:02 AM   #15
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And not the only reason. If you can't see them back there they could fall overboard and you'd wouldn't know it for miles.
No one has seat back there underway but itís a good point. I do have a camera in the pilothouse for the aft deck.
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Old 02-01-2023, 10:12 AM   #16
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Wow...hundreds if thousands of boats and rarely an issue if everyone is awake.

Hard to be on a course for so long that outside in open air even with station wagon effect that a big dose would be had. Open doors with no flow though could be a little worse.

Look at sportfish design who often troll all day.

If worried, a detector or two starts chirping wayyyy before it is an issue.
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Old 02-01-2023, 02:47 PM   #17
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Thank you all for your thoughtful responses!
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Old 02-01-2023, 05:20 PM   #18
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We were at Lake Powell for an Operational Exercise. About 14 people took a pleasure cruise to Rainbow Bridge on a 42 sportsfisher. About half way there 4 people passed out, 5 or 6 felt terrible and the rest were fine. They had a seaplane fly in and picked up the unconscious people, crushed one persons hand coming alongside. 2 of the unconscious people then were flown by Life Flight to Phoenix. They all lived but if it had not been for the seaplane they think some would have died. Interesting, the unconscious people were not in one area but sitting in different places on the boat. Apparently no one was paying much attention because it should have been caught before it got so bad.

I was on a sedan cruiser on a smaller lake in Arizona. The fumes were pretty bad but the owner claimed it was fine. I decided to terminate the patrol and had the CG stop issuing orders to him until he came up with a written plan on how to deal with the exhaust.

Moral of the story is that I always try to keep an eye on any crew to see if anyone is having a problem. I use the 2 challenge rule, if I ask them something 2 times and they are not responding properly then there is likely a problem and it needs to be addressed immediately. A lot of our CG training has bled over into our personal cruising and I think we are much safer because of it.
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Old 02-01-2023, 05:25 PM   #19
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Awareness of about 99.99% of dangers in life will keep you out of trouble.

The reoccurring statement from people in bad situations is usually "I never knew........."

This site is a haven for fearmongering........ people who seem to be worried about pretty obvious things that are no big deal for the average intelligent person who bothers to do a little research on their chosen hobby.
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Old 02-06-2023, 04:01 PM   #20
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Agreed re. gas vs. diesel, however, all vessels, regardless of whether or not they have CO-producing devices, are required to have CO detectors if they have enclosed cabin spaces, for ABYC compliance. Why anyone would risk this, or go without smoke detectors, continues to baffle me.

More here https://stevedmarineconsulting.com/co-poisoning/
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