F-L 120 (1969) exhaust system question

[Tazling]

I'll try to get some good pics of this and update later, because it's hard to describe, but my FL 120 has a non-standard exhaust system that looks pretty strange to me....

From the back of the engine just at water injection point emerges a monster stainless steel pipe maybe 4 inch diam. It wanders off to port, meeting up with an equally monstrous circular flange (like something off a submarine) also of SS, with quite a number of big fat bolts holding it together. After that, there's a pipe of some material or other (iron at a guess?) wrapped in FG cloth held on by spiraled wire. That pipe then goes into a complicated looking water muffler thing -- stainless also? -- which is mounted high up under the deck, and then it looks like (phew) conventional black exhaust hose goes aft to the exhaust port on the transom.

It's an odd looking setup and has clearly reached its best-by, 'cos I'm seeing stray carbon under the monster flange, also rusty drip marks and corroded, spongy bits of wire that have fallen off. I think it's really on its last legs. Also the spiffy SS pipe exiting the engine is pinholed at one welded angle -- it's been patch welded, but the patch is failing, and I've JB-welded over it just to get through the summer. That stopped the pinhole seep... But clearly Something Must Be Done.

So I was wondering if any of y'all with FL-120s -- preferably a GB32 but a 36 would probably be helpful too -- might be willing to share pics of your exhaust systems so I can see what variations there are, and what I might replace this impressive but aging work of art with.

 

[BruceK]

Without a photo, it`s not easy. The FL120 exhausts on my last boat(an IG not a GB) were as uncomplicated as yours are complicated. I suggest proceed with caution, there must be a reason, one possibility is the boat inhaled seawater via the exhaust and "hydrauliced", thus the elaborate system incl a high mounted"water muffler thing" just under deck level.

 

[Max1]

36' Marine Trader (1976) here.

I have a 4" exhaust hose about 5' long coming from the elbow to a cannister located just aft of the engine. From there, the cannister has another fitting for a 4" exhaust hose that goes to port but then makes a gentle sweep towards the aft such that the pipe lays against the hull running all the way to the back. There is one 4" joiner along the way. That's pretty much it.

Curious to see what your photos will reveal.

From the engine looking to the rear:

From the cannister looking at the port side:

PS: Please forgive the junkiness of the boat. This is very much a project boat and I have a lot of spare parts lying around in the engine compartment while I work on it. We've been in the water all summer so my restoration comes to a halt while we enjoy the boat during the summer. Cheers!

 

[Xlantic]

I'll try to get some good pics of this and update later, because it's hard to describe, but my FL 120 has a non-standard exhaust system that looks pretty strange to me....

From the back of the engine just at water injection point emerges a monster stainless steel pipe maybe 4 inch diam. It wanders off to port, meeting up with an equally monstrous circular flange (like something off a submarine) also of SS, with quite a number of big fat bolts holding it together. After that, there's a pipe of some material or other (iron at a guess?) wrapped in FG cloth held on by spiraled wire. That pipe then goes into a complicated looking water muffler thing -- stainless also? -- which is mounted high up under the deck, and then it looks like (phew) conventional black exhaust hose goes aft to the exhaust port on the transom.

It's an odd looking setup and has clearly reached its best-by, 'cos I'm seeing stray carbon under the monster flange, also rusty drip marks and corroded, spongy bits of wire that have fallen off. I think it's really on its last legs. Also the spiffy SS pipe exiting the engine is pinholed at one welded angle -- it's been patch welded, but the patch is failing, and I've JB-welded over it just to get through the summer. That stopped the pinhole seep... But clearly Something Must Be Done.

So I was wondering if any of y'all with FL-120s -- preferably a GB32 but a 36 would probably be helpful too -- might be willing to share pics of your exhaust systems so I can see what variations there are, and what I might replace this impressive but aging work of art with.

Could be a jacketed water-cooled riser going up to the water injector high-up.

So the first section could be a jacketed water-cooled riser followed by an insulated riser followed by the water-injector and then the hose. After that you may have a muffler and/or a water-lift.

I don't like water-cooled risers as they can corrode and leak water into the exhaust manifold and into the cylinder (ask me why I know).

 

[Marco Flamingo]

My Lehman has a custom SS exhaust. Lehman originally offered two different cast iron manifold take-offs, the "elbow" shown above by Max1 (with the raw water injection point being very close to the manifold), and a straight fitting that was threaded to fit pipe. I don't think the second version is still available. My original owner (in the 1980s) had the straight section welded to a SS riser that goes about a foot above the manifold before pointing down and having the coolant water injected. The cast iron on mine is pitted inside and out and will likely be the point of failure. The SS section is still in perfect condition. It is shown here as bare, but it has a fiberglass tape wrapping and a commercially made heat jacket that fits over it. Even where the saltwater is injected into the hot SS pipe isn't corroded. Surprised yours seems to be getting eaten up.

 

[Xlantic]

Here is the custom exhaust for my Cummins 6B naturals.

(The exhaust section between the manifold and the water injector bare in the photograph but is wrapped in fibreglass tape during operation.)

 

[Tazling]

https://www.flickr.com/photos/184710494@N06/albums/72177720311476888

here's an album of pics of my mad exhaust system.

Xlantic nailed it. It's a jacketed system. The first section of pipe is jacketed (runs nice and cool) but after that the saltwater is diverted into a smaller diameter pipe and rises to the top of the water muffler where it is dumped in through a port off-centre (aft).

The hot dry exhaust meanwhile continues through a flange, into a section of plain metal pipe wrapped with fibreglass cloth held on by spiraled wire, into a second flange and a 90 deg elbow which enters the water muffler from below. So that's a hot pipe, and sure looks like it.

Then the water and exhaust gas leave the water muffler together via a normal flexible exhaust hose, heading behind the fuel tank to port, eventually reaching the exit port on the transom.

There is a pinhole in the jacketed pipe's outer wall (underneath) not far from the engine, which has been repaired once (mfr confirms repair 2006). But the other end (at the water muffler) is a real mess.

The wire spiral wrap is rotting (I think it's just baling wire, nasty potmetal stuff) and falling off in bits. The 2nd flange (right before the 90deg elbow that goes up into the muffler) looks totally black with rust (and carbon?); the elbow itself looks thoroughly cooked and heat-fatigued, and there's some pinholing there barely weeping carbon moondust and the occasional drip of warm brine onto the hull planking.

It's a scary picture (or several).

The mfr of this interesting gizmo is

https://www.nationalmarineexhaust.com/

National Marine Exhaust in WA, USA. I have asked them about spare parts but I suspect the whole darned thing is custom welded.

So the pressing question for me is this: is all this really necessary?

Do we have to put the water muffler way up in the air to get enough rise for good drainage down to the transom? how far above waterline is the exhaust manifold on the engine? is there a stock Ford Lehman solution out there, or is everyone's exhaust system completely custom? if I were to go with a simpler system with immediate injection and, say, a Vetus water muffler a bit lower down, would I be at risk of backflooding the engine with saltchuck in following seas?

Inquiring minds want to know, as I don't really trust this spiffy stainless wonder to hold together much longer, and to tell the truth am not thrilled about the amount of weight being cantilevered off the back of the engine block... wd really like to reduce the amount of heavy metal pipe and replace as much as possible with exhaust hose, also a rustproof plastic or fibreglass muffler.

 

[Xlantic]

There are different ways to design the wet exhaust system but several principles must be adhered to.

Dave Gerr's Boat Mechanical Systems Handbook is a great guide for the proper design of exhaust and other critical boat systems.

The Vetus site also gives information and solutions.

As I mentioned above, I would avoid jacketed riser as a leak on the inside wall, even a pin hole like the one repaired on the outside wall of your riser, will lead to water entering the cylinders and causing havoc. I suspect your system is a time-bomb. Before I replaced the engines in my current boat it had a massive, complex jacketed system that failed and led to a seized engine.

I had Lehman 120s in a GB42 I had a few years ago. It had a standard exhaust elbow from American Diesel and a water-lift muffler. Even that failed and I had water intrusion into the number 6 cylinder in BOTH engines. At the time the boat was in a swinging mooring in a port busy with large ferries, cruise ships and other large boats travelling close by. I suspect water was forced in through the stern exhaust outlets by the waves from the passing ferries and other ships. Exhaust flaps may have avoided the problem.

So, I like dry risers and high water-injection points which is the system I have now.

 

[Max1]

https://www.flickr.com/photos/184710494@N06/albums/72177720311476888

here's an album of pics of my mad exhaust system.

wow. I'm getting a headache just looking at those pictures. Seems overly complicated.

 

[Tazling]

There are different ways to design the wet exhaust system but several principles must be adhered to.

Dave Gerr's Boat Mechanical Systems Handbook is a great guide for the proper design of exhaust and other critical boat systems.

The Vetus site also gives information and solutions.

[...]

So, I like dry risers and high water-injection points which is the system I have now.

Very helpful thanks. What's your opinion of a flapper for the port on the transom, to block backflow from waves/wakes?

I agree that a high riser and a stock water muffler are the way to go -- the geometry of the GB32 is challenging (as with most motor vessels of this type the engine is quite low and the exhaust port at waterline is only inches lower than the exhaust manifold outlet on the engine). The high riser will make access to the engine compartment trickier though (another darned thing to wriggle carefully around)... I'm gonna consult with American Diesel, but it seems like the right way is a high riser with as high as possible an injection point, then water muffler raised up as high as I can get it, before entering the "drain pipe" downhill to the transom.

Agreed the jacket system, while clever, seems far too complicated and liable to unannounced, invisible failure. At least when a conventional riser rusts out you can see it happening...

 

[twistedtree]

I would guess that aside from the jacketed section coming off the engine, the entire exhaust is dry, not wet. That looks like a dry muffler. And the wrapped section between the two flanges I'm guessing is a flex section. I'm quite surprised to see so much pipe rigidly attached to the engines is all these systems. They seem to be working fine, but all the manufacturer's I have experience with want to see a flex section pretty much immediately after the exhaust departs from the engine manifold or turbo. I had a boat where this wasn't done correctly and the vibrating exhaust structure ripped the turbo off the manifold, twice, before we wised up an installed a flex section.

 

[twistedtree]

A few other things. Marine Exhaust in Marysville is a very good exhaust fabricator. It may be old and end of life, but they are top notch.


This unusual exhaust arrangement was most likely done in response to a problem - probably engine flooding. Be sure you don't return to the original problem.


An exhaust flap can help with slapping wave action, but really can't be relied on since they can fail, get stuck, etc. The exhaust geometry and gravity need to protect the engine. Anything else is belts and suspenders.


To one of your earlier questions, marine exhaust systems are essentially 100% custom across all boats. There are various manufactured components that are used like mufflers and pipe sections, but the arrangement and assembly is all custom.

 

[mvweebles]

....
This unusual exhaust arrangement was most likely done in response to a problem - probably engine flooding. Be sure you don't return to the original problem.....

Good point.

I scrolled through the OPs picture album and could not make heads or tales of the pictures as they are all close ups. Also no idea of the general configuration of your boat and the engine/manifold relative to waterline. Attached is a diagram from a Northern Lights article by Bob Senter "Please don't drown me." It provides general guidance on wet exhaust install and configuration parameters. As TT says, virtually all marine exhaust systems end up with some degree of customization. From what little I can gather from OP and pictures, he appears to have some form of the 3rd version in the attached picture which implies the engine is deep in the bilge, well below waterline making it impossible to have enough drop from exhaust manifold to lift muffler. But only a guess without more information.

Bottom line is you need to view the exhaust as a system starting from the manifold. Just viewing the riser/elbow in isolation could easily have seriously undesired results (TTs point I quoted above). It's often difficult to get enough rise on the exhaust hose to keep the engine dry in all conditions which leads to premature engine death.

Good luck. This can be surprisingly challenging.

Peter

 

[Xlantic]

Very helpful thanks. What's your opinion of a flapper for the port on the transom, to block backflow from waves/wakes?

I agree that a high riser and a stock water muffler are the way to go -- the geometry of the GB32 is challenging (as with most motor vessels of this type the engine is quite low and the exhaust port at waterline is only inches lower than the exhaust manifold outlet on the engine). The high riser will make access to the engine compartment trickier though (another darned thing to wriggle carefully around)... I'm gonna consult with American Diesel, but it seems like the right way is a high riser with as high as possible an injection point, then water muffler raised up as high as I can get it, before entering the "drain pipe" downhill to the transom.

Agreed the jacket system, while clever, seems far too complicated and liable to unannounced, invisible failure. At least when a conventional riser rusts out you can see it happening...

I think flappers can be useful in certain situations. For example, as I mentioned above, in a busy port where there is a chance of waves of passing ships driving water up the stern exhausts.

Gerr recommends them, as he does dry rather than wet risers. The sketch below is from his Boat Mechanical Systems Handbook:

 

[Tazling]

I would guess that aside from the jacketed section coming off the engine, the entire exhaust is dry, not wet.[...]

It's wet except for the wrapped section... water comes sploshing out at the transom

Water comes in the top of the can, exhaust gases come in the bottom, then they both go out the side...

 

[Max1]

It's wet except for the wrapped section... water comes sploshing out at the transom

Water comes in the top of the can, exhaust gases come in the bottom, then they both go out the side...

That is a very interesting exhaust system.

 

[Tazling]

That is a very interesting exhaust system.

Yep, "interesting" is the word I think .

What bugs me about it is the jacketed section. A pinhole in the inner tube wall would be invisible and potentially catastrophic -- I prefer my pinholes where I can see them...

 

[BruceK]

FWIW, I had the std Lehman exhaust angle with injector, leading to a heavy "flexible rubber" exhaust pipe, into a right angle fiberglass tube(just to change direction) with a further flexible pipe into an aftermarket fiberglass muffler. Out of the muffler another flexible pipe to the transom. All downhill,nothing elevated,no issues in 10 years. There has to be a reason yours was done that way,please don`t find out the hard way.

 

[Xlantic]

That is a very interesting exhaust system.

I believe it used to be a common system to mix the exhaust and the cooling water.

Gerr describes it his handbook, calling it a "standpipe exhaust system". I personally don't like this design, particularly the "new" version as water can get through to the manifold if the unseen deflector cap corrodes and fails.

The previous engines in my 1973 GB50 had this system, together with water-jacketed risers. They were AmMarine engines, General Motor Toroflo engines marinized by Grand Banks themself, then called American Marine.

Two years ago something failed, water entered a cylinder and one engine seized. I suspect what failed was one of the massive and highly complex jacketed risers but it could have been the standpipe's deflector.

 

[esheufelt]

Showerhead exhaust riser

I have the same setup exactly. Also from National Marine exhaust. I'm repowering so just pulled it all out.

The way it's designed there is no standing water in the bottom. Mine was 38 yrs old and not leaking. Which is about 3 times older than anything else I've seen.

I'm pretty sure I'm going back to them to replicate it in 5" wet instead of the 8" it was with the 3208.

 

[Nepidae]

FL Exhaust

Any questions of this type that could have an impact on the engine operation the question should be addressed to Brian at American Diesel (https://americandieselcorp.com/).

He is the ONLY expert on these engines.

ANY home built solution could be disastrous. Let Brian know and go by his words, PERIOD.

 

[Steve DAntonio]

Agree with TT, this looks unnecessarily complex. Following some basic guidelines for the design of combination dry/wet exhaust risers, I suspect you could simplify this. A dedicated marine exhaust manufacturer also won't build a design that is wring, or prone to failure/flooding. Support for risers is critical and so very often lacking.

This article may be helpful https://stevedmarineconsulting.com/wp-content/uploads/2014/03/ExhaustSystems170-FINAL.pdf

Bound for the International Boat Builder's Exhibition in Tampa

 

[esheufelt]

showerhead riser

I looked at your pictures more closely. Mine is slightly different. I'm dry and wrapped from the turbo to the riser flange but otherwise the same.

This setup meets the Seaboard Marine design guidelines very well. My injection point is 40" above the waterline and the riser spillover is 20" below the injection point. You could crank for 20 minutes and not flood your engine.