Rear exhaust on 31 Commander rolling back.....anyone corrected this?

We have a 31 Commander and the exhaust dumps out the back under the swim platform.  If we have the forward windows open we're good but in the winter or cooler weather with the windows closed, we get exhaust rolling back over the transom.  Has anyone added 90 degree bellows to the ends of the exhaust to help divert the exhaust? Or is there a better solution?  Any help is appreciated!

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I had exhaust fumes getting into my boat while underway. I own a 35' CCC. There was a lengthy discussion on here regarding this but the abbreviated version is that even though the engines started great and ran very well, they were still not running perfect. A tuneup and eventually having one of the carbs rebuilt solved my issue of exhaust fumes. I will try to find the old discussion and post it here.

Thank you Steve, I'll take a look at that thread.

This is known as "The station wagon affect". Remember when you were kid and you road in the back of the station wagon with the back window down. we were getting our daily dose of CO poisoning. That's why we slept so well on those long car rides. Every internal combustion engine, no matter how well tuned, produces CO. The effects of co on people mimics sea sickness. Our body prefers co and absorbs it 100 times more easily the oxygen. Under the right conditions, exhaust fumes will roll up the transom and into the cockpit of a moving boat. I have a picture of a friends 32 Carver Convertible cruising at 18 knots and the flag on the stern is flying into the cockpit. 

I installed 2 smoke/co detectors on Wanderer, 1 in the salon, 1 in the v-berth.

There was a story in the BoatUS magazine recently of a young boy who rode on the transom of a ski boat on the way back to the marina. Upon docking, he fell into the water. They pulled him out and he was deceased from CO poisoning. Kids absorb it more readily than adults. 

To answer your question, there are turndown pipes that disperse the exhaust under water. Can't remember the name of it right now.

The only time I have exhaust coming into the cockpit on my 31 is when the wind is behind me blowing faster than I'm cruising. I wonder of my canvas has something to do with it, changing the airflow over the back. 

I try and run with the hatch in the v berth open.  Seems to help

Our 31 is a sedan flybridge. We keep the back door shut at all times when running. At times on the flybridge I can even feel a mist on my back while running. The Forward hatch has a vent in it to let in some air but not much. We spend a lot of time in choppy water so having windows open is not an option. The problem with down turned exhaust is that you can't see if its pumping water. Also at planing speed the exhaust will be out of the water anyway. Dave

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