Wet exhaust tail pipe flappers…pros and cons?

[Southern Boater]

What are the forum’s thoughts regarding wet exhaust systems external flappers on the tail pipes?
The recent discussion about repowering the Manatee after waves were driven up the exhaust pipe, as well as some local instances of a similar situation resulting in hydraulic locked engines, has me considering adding them to my own exhaust pipes.

What are your thoughts/advice, recommendations for a better quality product etc?

TIA.

 

[DavidM]

They can stick open and flood your engine. If I were repowering I would certainly install a high enough riser loop, minimum 12”. But for an existing installation, a flapper valve is much better than nothing. Maybe couple that with a surge tube.

David

 

[Comodave]

I don’t see how they could hurt anything.

 

[Keysdisease]

There are several reasons in the positive column
And very few if any in the negative column

Best value in reducing the chance of hydrolock available.

 

[O C Diver]

I had one on my charter boat and thought it was doing what it was supposed to be doing. The next owner of the boat ended up replacing the turbo as a result of corrosion. IMO, it's a poor substitute for a properly designed exhaust system. Whether you have a high riser before the wet exhaust elbow or use a lift muffler to accomplish the same, it only takes one bad event with a flapper to ruin your engine.

Ted

 

[Northern Spy]

If nothing else it directs the outflow downwards which I find maintains a cleaner stern. May prevent wildlife entry. May help in a following sea or backing down.

I have one, but I also have a waterlock after my riser and a gooseneck in the lazarette as well.

Belt and suspenders (and I guess another belt).

 

[Insequent]

I have a high riser before the water injection point. a water lift muffler, a check valve unit and finally rubber exhaust flappers. It is a good system design by Port Townsend Shipwright's CoOp.

Flappers should be regarded as an add on, not the key element for preventing issues from surge etc

 

[Southern Boater]

They can stick open and flood your engine. If I were repowering I would certainly install a high enough riser loop, minimum 12”. But for an existing installation, a flapper valve is much better than nothing. Maybe couple that with a surge tube.

David

My existing arrangement is the lowest part of the exhaust elbow outflow is 14” above the waterline, then down to a 2 foot (600mm) high water trap muffler. Once the 6” exhaust tube leaves the engine room it travels 13 feet (4 metres) to the transom and the open tail pipe.

I don’t understand what a surge tube is?

 

[Southern Boater]

I have a high riser before the water injection point. a water lift muffler, a check valve unit and finally rubber exhaust flappers. It is a good system design by Port Townsend Shipwright's CoOp.

Flappers should be regarded as an add on, not the key element for preventing issues from surge etc

Any recommendations on a particular brand Brian, I guess yours were already installed prior to your boats relocation to Oz.

 

[Southern Boater]

If nothing else it directs the outflow downwards which I find maintains a cleaner stern. May prevent wildlife entry. May help in a following sea or backing down.

I have one, but I also have a waterlock after my riser and a gooseneck in the lazarette as well.

Belt and suspenders (and I guess another belt).

We have had small birds inside one winter, it’s a good point, thanks

 

[Southern Boater]

I had one on my charter boat and thought it was doing what it was supposed to be doing. The next owner of the boat ended up replacing the turbo as a result of corrosion. IMO, it's a poor substitute for a properly designed exhaust system. Whether you have a high riser before the wet exhaust elbow or use a lift muffler to accomplish the same, it only takes one bad event with a flapper to ruin your engine.

Ted

Is this the externally clamped rubber flappers you are referring to Ted, or something internally fitted?

 

[Southern Boater]

There are several reasons in the positive column
And very few if any in the negative column

Best value in reducing the chance of hydrolock available.

I was hoping for a positive result. Many that I have seen appear to “curl”, perhaps due to heat, but assume you don’t want anything that is stiff to open and close to restrict exhaust gases from escaping easily.

 

[Insequent]

Any recommendations on a particular brand Brian, I guess yours were already installed prior to your boats relocation to Oz.

I checked my spreadsheet tabulation of invoices before posting, and unfortunately there are no brand details.

And yes, my rubber flappers have some curl, but they would still stop a wave from behind at anchor. Underway the exhaust pressure might keep the flap partly open.

 

[O C Diver]

Is this the externally clamped rubber flappers you are referring to Ted, or something internally fitted?

Yes, mine was of the style that was externally hose clamped. I would guess on average that they lasted 4 or 5 seasons. What seemed to work better for me was using a 6" flapper on a 5" exhast pipe. You basically cut the ring near the bottom, that installs around the outside of the pipe before clamping it on. The larger sizes seemed to have thicker flaps that didn't curl as much.

Ted

 

[Southern Boater]

Yes, mine was of the style that was externally hose clamped. I would guess on average that they lasted 4 or 5 seasons. What seemed to work better for me was using a 6" flapper on a 5" exhast pipe. You basically cut the ring near the bottom, that installs around the outside of the pipe before clamping it on. The larger sizes seemed to have thicker flaps that didn't curl as much.

Ted

Ah, good point, it makes sense, thank you for the suggestion.

 

[Keysdisease]

I don’t understand what a surge tube is?[/QUOTE]

A surge tube reduces the chance of "temporary" (hence surge) water from reaching the exhaust riser. I see these commonly on Sportfish so when they back down chasing a fish the water "surges" into the horizontal tube and not uphill to the riser.

 

[Xlantic]

What are the forum’s thoughts regarding wet exhaust systems external flappers on the tail pipes?
The recent discussion about repowering the Manatee after waves were driven up the exhaust pipe, as well as some local instances of a similar situation resulting in hydraulic locked engines, has me considering adding them to my own exhaust pipes.

When I read the post on the Manatee repowering I also thought of exhaust flaps.

If the stern of a docked boat is exposed to waves for whatever reason I think flaps are useful.

If I recall correctly Dave Gerr recommends them in his "Boat Mechanical Systems Handbook".

In my previous boat, a 1979 GB 40, I had water enter the no.6 cylinder in both engines while moored on a swinging buoy in a busy port over a winter. Luckily I was able to save the engines and just had to replace the pistons with the engines in place.

 

[O C Diver]

When looking at HealHustler's Manatee, the simple solution (IMO) was to use a lift muffler, run the exhaust from the muffler under the deck and then up the transom (it's hollow), turn it down, and run it out the exhaust port. From a foggy memory, I think you could go about a foot above the deck and then turn it down.

Ted

 

[Mac G]

In my previous boat, a 1979 GB 40, I had water enter the no.6 cylinder in both engines while moored on a swinging buoy in a busy port over a winter. Luckily I was able to save the engines and just had to replace the pistons with the engines in place.

Am curious if you could expound on the design of your exhaust system that would have allowed that.
Would like to know because am presently reworking my own exhaust and always keen to learn more, from others.
Thank you

 

[Xlantic]

It was a standard water-lift muffler system for the 120 hp Ford-Lehmans with the stock exhaust elbow.

Where it was moored, there was regular boat traffic, including large ferries, cargo ships and even cruise ships. Because my boat was on a swinging mooring the stern could be exposed to the waves of these passing boats.

My guess is that the periodic waves hitting the stern may have been large enough or hit some kind of resonance that filled the water-lift muffler and pushed some water into the nº. 6 cylinders.

I had the boat for several years afterwards in a more protected dock and did not have any more problems.

(When I repowered my current boat I had some custom dry-risers built that go over a foot above the exhaust manifolds.)

 

[Mac G]

Okay. Thank you.
Have removed my conventional cast-iron mixing elbows that were bolted directly to the back of the manifolds and am creating dry hot (insulated) risers that will loop up above the height of the mufflers exit spillover points for that very reason.
Will then inject raw water downstream of those high loops so it (hopefully) will be a physical impossibility to ever get seawater back into the engines.
Challenge will be insulating the crap out of the hot risers and engine room overhead to eliminate fire risk.

 

[Xlantic]

I used fibre glass insulation wrap for motor cycle exhaust and metal "cable ties" to hold it in place.

There are fancier insulation solutions as well.

 

[Southern Boater]

I don’t understand what a surge tube is?

A surge tube reduces the chance of "temporary" (hence surge) water from reaching the exhaust riser. I see these commonly on Sportfish so when they back down chasing a fish the water "surges" into the horizontal tube and not uphill to the riser.

[/QUOTE]

Thanks for that, it makes sense

 

[Northern Spy]

Vetus has some decent information online about exhaust design and components.


Mine looks like the one on the right.

 

[Brooksie]

Not really unusual to have to replace turbo output housing after some years due just to saltwater atmosphere in exhaust tubing, even a properly designed one.

I think a flapper can be of use in some conditions.

However, anchored in a seaway, pitching 14" can overcome a 14" riser of course, as can wakes while tied in your ship.
A water lift muffler will, under the same conditions, eventually fill & then flood the engine. It is the gooseneck (which can only be used with a waterlift) that can save the day. Even with this, the saltwater atmosphere in the exhaust is still a long term distructive force.

 

[DavidM]

Here is a drawing offered by Tony Athens of the minimum dimensions for a safe exhaust system. When the "point" referenced in the drawing is several inches below the spill over point then the water will run back out the exhaust and not get into the engine.

David

 

[Keysdisease]

Without question getting the exhaust as high as possible is best practice, and as mentioned flappers should be considered secondary to a well designed exhaust system. That said they can't hurt, and do provide some protection along with secondary benefits previously mentioned.

An "almost" (because weird stuff happens on boats) bulletproof exhaust system would have a lift muffler that would exhaust up to a simple gas/water separator like you see on gensets. Any water that surges up the exhaust would just drain out the exhaust gas/water separator drain and never make it to even the lift muffler let alone uphill to the mixer.
Any of the wet exhaust companies (Soundown/Centek/Marine Muffler) can make these simple "plate separators" and as long as everything is sized correctly and you don't lift from the lift muffler to the separator more than about 4ft the backpressure on most engines should stay in spec.




Something like this:

 

[BruceK]

Wonder if this risk is why some boats mine included have the exhausts at 45 degrees where transom and hull meet.

 

[Keysdisease]

Wonder if this risk is why some boats mine included have the exhausts at 45 degrees where transom and hull meet.

Perhaps some, but the unique circumstances for water to back up an exhaust pipe are still present in a 45* corner outlet. I believe the two main reasons for that configuration are noise and soot. It is more difficult (expensive) to do it that way, easier to come straight out a transom.

Much exhaust noise heard on a vessel is reflective noise off the wake. By exiting at 45* this reflective noise is reduced.

And the "station wagon" effect is reduced by the 45* exit as well. By exiting into the air coming of the side of the boat exhaust is carried more aft and not into the low pressure area immediately behind the broad, flat transom when underway. This keeps the transom cleaner and exhaust odors are reduced.

 

[jleonard]

I put a flapper on my old Mainship 34. It made me feel better