Will it Float?

[cjflanagan]

Mercruiser Magnum 350 ~ Alpha 1 combination w factory /Thru-Hull Exhaust. Transome plate where exhaust would have gone thru is factory sealed with a metal plate. Do I need an exhaust bellows if the transome plate is sealed?<br /><br />BP

 

[cjflanagan]

Re: Will it Float?

Do you need an exhaust bellows if you have thru hull exhaust?

 

[ziggy]

Re: Will it Float?

i want to try my educated GUESS for this one. i would think, no. from what i understand, the exhust bellows is the least important as what keeps the water from comeing in the engine is the riser and the flapper. that's after the metel plate going back to front. the ehaust bellows themselfs can even leak and have tears in them. the bellows would be between the elbow and the back of the upper which leads to sea water thru the prop. all of the area from prop to elbow up to the flappers may have water level in it at rest. so. if ya got a block off plate on the transom plate instead of a elbow. the water stops there. <br />more guessing but i'd think that you would have flappers on your open ehaust and risers next to prevent water intrusion into the engine. <br />that's my guess.............feel freely to correct me so i don't lead boiling point 212 wrong way.

 

[rbezdon]

Re: Will it Float?

I think you are mostly right Ziggy. The exhaust is not sealed for water. The way it works is to have a riser system significantly higher that the boat water line to prevent intrusion of water into the boat through the exhaust port. The bellows is simply a channel for the exhaust gasses to get away from the transom. In fact, my bellows is full of holes all along its length by design for back pressure relief. The only thing I am sure is not correct is that the flappers stop the water from coming. The water stops completely as a result of the static line being higher than the boat water line. The flappers are for a water surge such as when the wake splashes up against the transom when coming down off plane in a sudden slow down of the boat. The wake causes a surge of water which could, if it hits right, force water up the exhaust system (even more so at very low idle or a stalled engine condition) and into the engine and boat. The flappers will slow or stop most of the water but they do not seal tight. Don S has made a point of this in several other posting as well. Flappers do not and can not stop all water ingression, they just prevent major ingression. That is why flappers are needed even with through hull exhaust as well. If the exhaust outlets are any where near the water line, the back wash from the wake or waves hitting the transome (particularly common in reverse) could let water ingress when the exhaust flow is very low at idle or if the engine stalls.

 

[ziggy]

Re: Will it Float?

vatter41, you said it better than i. the static waterline of the boat is how far the water would be up into the exhaust when at rest. and it would be below the flappers. i did a poor job of discribing that the flappers do not stop water from going beyond them. they just slow it down as you stated. the risers are what stops it from flowing into the engine as the risers are hopefully way above the static waterline. following sea (gettin chased by a wave that overtakes ya from behind)would be the other situation that flappers help to slow down the water comeing back up the exhaust. along with sudden stops and reverse as you stated. thanks for sayin it better than me. happy boatin.........<br />ps, i read dons's post on flappers too. very good post.....sorry boiling point 212, i didn't mean to turn this into a flapper post.....

 

[QC]

Re: Will it Float?

I think you guys are missing something. He has thru-hull exhaust. His question is, does he need the exhaust belows with thru-hull exhaust. I am not sure about any other need for the exhaust belows, but this is not about water getting into the manifolds through the bellows as there is no connection from the bellows to his manifolds now . . . His flappers are probably in the end of the the thru-hull like mine.<br /><br />This is a Bravo, but you can see the bellows doesn't even meet the flange on the drive with mine, and there is a solid plate between the bellows and the transom assembly.<br /><br />

<br /><br />Here is one of my flappers:<br /><br />

<br /><br />Someone needs to confirm, but I see no value to my bellows as there isn't even any connection unless the trim is all of the way down. They put that hose on for something, but the picture I took is still within the normal "trim" range, so I can't see how it does anything.

 

[rbezdon]

Re: Will it Float?

You are right Quiet cat, but I think we made both points. The plate pevents water from coming into the boat, end of story. It can enter the bellows hole but stops at the plate. What good is the bellows at all??

 

[QC]

Re: Will it Float?

Yeah, when I reread I think Ziggy and you both get there, but it seemed like we were talking a lot about water entering instead of the question. I was kinda looking for clarification too, becasue my bellows just sort of sits there doing nothing.<br /><br />No prah dude, just thought a couple of pictures might help too.

 

[cjflanagan]

Re: Will it Float?

Thanks so much guys. IXNAY ON THE EXAUST - BELLOWSNAY. I owe ya'll one.<br /><br />BP