Exhaust backdraft?

[saburke17]

Hey guys, what would cause the exhaust to be pushed/sucked backwards towards the helm? On my trip i noticed that when my front strataglass was down there was noticeable diesel exhaust smell being sucked into the helm while i was steaming forward at 20 knots, Any idea's?

Sean

[mike ohlstein]

https://grandlakeliving.com/boating-2/p ... poisoning/

[Carl]

You'd think going along at a good clip with exhaust shooting out the back would have the exhaust fumes left way behind you.
But that is not always the case. As the wind and breeze comes around your boats top and side it creates a low pressure area behind your boat pulling the exhaust back into the cockpit, helm and cabin.

Ways to avoid it...if nice out I'll crack the forehatch a bit. Open helm window. Run at angles to the wind.

I have those rubber flappers and found angling them a few degrees and running a screw on the inside portion directed the exhaust to the outside edges of the transom which pulled a good amount of the exhaust away at some speeds. My wife hated gas fumes so it was a challenge...

I believe running the exhaust closer to the edges outside the stringers is better than having in the stock position. Something I thought about doing...might still. Having exhaust come out the sides is also supposed to help...but I hate the splashing of exhaust on the sides when not moving.

As per Mike's post...aside from the smell you need to be careful of Carbon monoxide poisoning.

[saburke17]

station wagon effect, i knew there was a name but couldn't think of it. Thanks guys!!

[mike ohlstein]

Get a Marine CO detector. The home ones won't stand up to the moisture.

[Tony Meola]

I only have an issue when running down wind if the wind is at a greater speed than I am running. I do not have any curtains up on the bridge. Try taking them down and see if they make a difference. Like Carl said, otherwise crack the hatch but in any kind of sea that means water getting into the v berth.

[Yannis]

You gotta ask those Blackfin guys...apparently their boats have this problem quite often.

[Carl]

I only have an issue when running down wind if the wind is at a greater speed than I am running. I do not have any curtains up on the bridge. Try taking them down and see if they make a difference. Like Carl said, otherwise crack the hatch but in any kind of sea that means water getting into the v berth.

Tony- If your up on the bridge without an enclosure it would be tough for you to get fumes coming back at you...unless as you said running downwind, slow troll in heavy air.

On my boat in heavy air (AKA- almost fog like, usually in early morning) the steam from my exhaust could be seen for quite some time. It reminded me of those wind tunnels where they inject smoke around a car or wing so you could see the flow. At cruise, it would blow out a couple feet and if it was a still day or going into the wind the steam billowed back to the transom and dispersed in the cockpit with a definite exhaust odor, especially if I had the helm window closed with enclosure up. You could see letting air through the boat, whether open hatch of window made a difference making the steam pileup just behind the boat, almost scary thinking lack of water flow or something wrong...but looking and flow along with a hand in the exhaust I knew it was ok and took awhile to get used to...that was till someone would come along not used to it and we started...that wrong, you not getting enough water blah blah blah. Then they'd get me thinking and it was hands on the manifold, risers, hoses, exhaust hose, feel the exhaust water...its fine, its normal.

Did it again...off the subject.

So the air and exhaust piles up behind the boat...without an air stream from inside the boat that exhaust definitely entered the cockpit, by helm area and into the cabin. Luckily being a boat in open water a couple degrees one way or the other had the breeze come enough across the transom to pull it away and I could see the exhaust steam trailing back in the distance. It also how I figured out what angling the flappers did...played when the air was heavy and I could watch the exhaust. All I had to do was get it to reach the corner and gone.
That didn't always work and I still got complaints...especially if Doreens family came out with us....they'd sit right at the back and complain about the exhaust.
Of course my answer of "then don't sit back there " was me being a wise guy with all the answers...Oh, but we like it here.
I can go faster so the exhaust doesn't sit right there...No we like going slow.
I can shut the engines!?...Stop being a wise arse, we have reservations.

Family, if I didn't love'em, I'd kill' em. Joking....about the kill'em part.


On some boats I've seen some ugly exhaust coverings that push the exhaust down into the water or directed it way off to the side. Being ugly I never pursued...not sure if a back pressure issue....but it depends on how much you want to cut down on the fumes.

[Tony Meola]

Carl

If I had a fume problem, my wife would be screaming at me. I have been in the cockpit with someone else running the boat and had no sense of fumes coming in the cockpit. I wonder if it has to do with the difference in design between the Fly bridge model and your Cabin structure.

[Carl]

Tony-

It might be...the house on the Express comes back bit further and I used to have the sides enclosed with clear curtains which I assume can make the air more turbulent in the cockpit sucking in more exhaust fumes. The FBC with a longer cockpit...more room for air to come in and mix. I don't know, it was a good long time since I've been on a FBC running and I never really paid much attention to the fumes...aside from it being mixed with salt air and smelling great.

...and I do get the transom being the best seat in the house and fumes can stink. But only so much you can do when you have 2 Big Block, Carburated 440 Motors idling you along at 7 or 8 mph, unless you have a cross wind or breeze those fumes are sitting right at the transom. Go figure, its where the exhaust comes out.
Tacking a bit works..but not when you have to get somewhere or in a channel.

When running, unless certain conditions come into play, its not much of an issue. Even going slow...usually not a problem...sometimes it is.

As I said, it's all good. Those times out with the family and friends are some of the best times on the boat. Pendulum swings both ways.