wind deflector on hull for exhaust opening, wallas 85DU

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primative

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Our stove was back drafting exhaust into the cabin yesterday. I called Scan and Doug suggested it was a combo. of boat speed and or wind. I agreed that I was in quite windy conditions. He suggested a cowl vent placed at the front edge of the exhaust opening would solve the problem. He said to check it out on Scans site under tech talk: http://www.scanmarineusa.com/techtalk.html
Under: Features and Issues Common to all Wallas Products.

In their pdf (techtalk_WallasProductTips.pdf) page 3, figure 1, is a graphic that has to be enlarged to read. It shows placement of the cowl vent, but there was no size info.

A question to those of you with experience of the "back draft" issue and correction with a cowl vent installation: What size/dimension? Did you place as recommended by Scan? Where did you purchase? Any other details you think may be important? Screw holes through the hull — you know!

thanks Tom and Rene
 
I installed one before Scan had their size and placement recommendation posted. So I used a smaller clamshell vent and modified it to make use of the aft two bolts which secure the Wallas flange to the hull. In order to do this, I squeezed it in a vise until the holes lined up and then filed notches in the apex of the clamshell so as to clear the front two Wallas flange bolts. In other words, the clamshell is secured by only the back two flange bolts. In this way I didn't have to drill any new holes in the hull.

In summary, the installation certainly didn't hurt anything, maybe helps in certain occasions, but does not entirely prevent the Wallas blackout issue. Even so, I think it's worth doing.
Al
 
Thanks for your input Al. I like the way you kept it clean, using the available exhaust flange screws.

I'm not sure what I'm going to do yet, but will probably follow Scan Marines instructions.

I wasn't sure from your summary whether you knew it's made a difference in reducing incidents for your unit? Is your stove an 85DU?

Yesterday I bought a Perko brand, clam shell ventilator at Sextons Marine , catalog No. 0339DP0CHR. It looks like it's a good match.

I'm hoping for more responses regarding whether there is improvement or not.

Thanks Tom and Rene
 
Our stove is a 125 DU, which I guess is a 95 DU with the blower top.

It's tough to say for sure whether it's made a difference or not. I mean, if we don't experience a blackout, did we prevent one from happening or were conditions just not right for one to occur? The best I can say is it doesn't hurt to put in a clamshell, but I do not think it is 100% cure for the situation.

Good luck,
Al
 
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