Exhaust Bellows

[MeanGene1]

I know this has been a topic in the past but I wanted to see if there has been any new concerns or advice.
I have a 2003 Kayot V200 Deckboat with a 5.0L Mercruiser I/O. This past fall my exhaust bellows came off the lower unit. I have seen several discussions replacing the bellows with an exhaust tube or a bravo tube. Is that still considered an equal or better option for a boat like mine? It does have a large rear swim platform. Does that create a concern?
My fear is propelling in shallow areas and channel trimmed up or reverse moving off a dock trimmed up. I have heard the only real issue is the exhaust is slightly louder which will not bother me.

 

[Scott06]

yes only slightly louder on plane, It would probably be the same volume as now with one end off the bellows...

 

[Bondo]

Ayuh,..... Welcome Aboard,...... No concerns,....
'n much easier to install,.....

 

[MeanGene1]

Ayuh,..... Welcome Aboard,...... No concerns,....
'n much easier to install,.....

Thank you!

 

[MeanGene1]

yes only slightly louder on plane, It would probably be the same volume as now with one end off the bellows...

Thank you!

 

[tank1949]

I know this has been a topic in the past but I wanted to see if there has been any new concerns or advice.
I have a 2003 Kayot V200 Deckboat with a 5.0L Mercruiser I/O. This past fall my exhaust bellows came off the lower unit. I have seen several discussions replacing the bellows with an exhaust tube or a bravo tube. Is that still considered an equal or better option for a boat like mine? It does have a large rear swim platform. Does that create a concern?
My fear is propelling in shallow areas and channel trimmed up or reverse moving off a dock trimmed up. I have heard the only real issue is the exhaust is slightly louder which will not bother me.

The exhaust bellows are a pain and poor design. I thought about drilling a tapping the transom side and the OD side with a couple of ss cap screws to provide a "bump" to restrict ss clamps from letting loose and sliding. But so far, mine have held.

 

[Eug5.0L]

This may be a stupid question but what prevents the water from going into the engine? Or into the manifolds etc?
Having a hard time visualizing the whole thing.

 

[MeanGene1]

I know this has been a topic in the past but I wanted to see if there has been any new concerns or advice.
I have a 2003 Kayot V200 Deckboat with a 5.0L Mercruiser I/O. This past fall my exhaust bellows came off the lower unit. I have seen several discussions replacing the bellows with an exhaust tube or a bravo tube. Is that still considered an equal or better option for a boat like mine? It does have a large rear swim platform. Does that create a concern?
My fear is propelling in shallow areas and channel trimmed up or reverse moving off a dock trimmed up. I have heard the only real issue is the exhaust is slightly louder which will not bother me.

What prevents water from going into the engine thru the exhaust?

 

[Scott06]

What prevents water from going into the engine thru the exhaust?

The height of the exhaust riser and elbows above the water line. Typically the boat manufacturer will install an engine such that there is 14-15” from water line to top of the exhaust elbows . This height difference keeps water from backflowing into engine... but it can happen in certain situations

 

[Scott06]

This may be a stupid question but what prevents the water from going into the engine? Or into the manifolds etc?
Having a hard time visualizing the whole thing.

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shows a diagram remember the exhaust goes up then does a series of 90s above the water line

 

[MeanGene1]

The height of the exhaust riser and elbows above the water line. Typically the boat manufacturer will install an engine such that there is 14-15” from water line to top of the exhaust elbows . This height difference keeps water from backflowing into engine... but it can happen in certain situations

Maybe I am being too paranoid about this but, would a boatload of people increase this risk? And what happens if it does take on water?
Does this risk go away with the proper exhaust bellows in of the exhaust tube?

 

[poconojoe]

This is why it's never good to make a sudden stop when you are at a decent speed. Water will rush toward your stern and up through the exhaust. Always power down gradually, never suddenly.
This is where the exhaust shutters come into play, sometimes called flappers.
They help against backflow of water. Sort of a check valve.

They are inside your exhaust risers.
They however are prone to heat damage. If your engine was ever overheated, they could be gone due to the rubber melting.
The only way to check them is to open it up and look.

 

[Stinnett21]

Maybe I am being too paranoid about this but, would a boatload of people increase this risk? And what happens if it does take on water?
Does this risk go away with the proper exhaust bellows in of the exhaust tube?

No more than with the bellows attached. Think about it...at rest with engine off water is consistently occupying the Y-pipe inside the boat, level with the water outside the boat with either bellows or tube. Now I have heard the argument that if you slip your boat or beach a lot the tube may offer a more direct path for wave action to play havoc. However, I would think that would be a very small chance. Next time my bell housing is off I'll be getting a tube.

 

[Scott06]

Maybe I am being too paranoid about this but, would a boatload of people increase this risk? And what happens if it does take on water?
Does this risk go away with the proper exhaust bellows in of the exhaust tube?

Yes a bunch of people on the stern or swim platform would increase the risk. I think this is built into the calulation from mercruiser, but I did notice on my boat (2004 Sea Ray 200) that Sea Ray adds a couple extra inches to the clearnace. They use no riser on this boat with a 4.3, but the 5.0 powered ones use a 3" riser I assume to over come the extra 100-150# lbs in the stern from the heavier engine. I repowered my boat from a 4.3 to a 5.0 and did not use the risers the factory would have (found this out later) just measured as the drawing was. In six years of use with tyoically 6-8 people in the boat, all on the stern when swimming, have had no issue.

Toyically you can get some water backflowing into the exhaust valves which wil lock up the engine (hydrolock). Starter wont turn engine, repeatedly trying can bend a connecting rod. Never happend to me, but you remove the spark plugs to spin it over expell the water then run it and change the oil if milky..
The exhaust bellow or tube makes no difference on this as they are open and full of water anyways. this allows the water to act like a muffler, plus the cooling water dumps into the exhaust to cool it.

 

[tank1949]

you may consider exhaust y pipe shutters. If working properly, they minimize water backflowing, but they are not perfect. I'd never abruptly cut motor while backing down. I blue water fish and I am always backing, but my motors are running and expelling gasses. All MC I/os boats are rear end heavy and I would think MC would install motors and risers with correct height. If you add extensions to risers, the additional height may interfere with closing motor hatches.

 

[Bondo]

Maybe I am being too paranoid about this but, would a boatload of people increase this risk? And what happens if it does take on water?
Does this risk go away with the proper exhaust bellows in of the exhaust tube?

Nope,.... No difference,.....

 

[achris]

... and I would think MC would install motors and risers with correct height. ...

MerCruiser don't install engines in boats, that's the job of the boat builder or the selling dealer. And as risers cost money, if it's 'borderline', they'll push it.

Chris......

 

[achris]

Here's how it works...

First the drawing, so we all understand what we're talking about.



Remember, at rest water will flood the exhaust system and the level of the water in the y-pipe will be the same as the level outside the boat, regardless of tube or bellows. The level of that water is what's important.

The blue waterline. This is a good level. The distance between the waterline and the top of the elbow (pink line) is more than the required 33cm.

But the red waterline, not so good. It's likely the height difference is less than 33cm, so a riser/s should be installed between the elbow and the manifold, to increase the height. Risers are available in 75mm and 150mm, and if you needed more than 150mm, then you can stack risers to get the required height.

Hope this helps,

Chris.....

 

[tank1949]

MerCruiser don't install engines in boats, that's the job of the boat builder or the selling dealer. And as risers cost money, if it's 'borderline', they'll push it.

Chris......

If the crap came back on them, the lawyers would settle it. Trust me.

 

[achris]

If the crap came back on them, the lawyers would settle it. Trust me.

No idea what you're talking about. Your sentence doesn't make any sense with reference to the comment you're quoting. Who is 'them'?