New anti siphon install in wet exhaust?

[albinalaska]

‘Ello all-

Have been getting into our lazarette (previous posts on my page) and that work has lead to some ideas of reconfiguring our wet exhaust system to ensure less water back-flow issues moving forward.

We’re looking at removing the check valves on the exhaust as I’ve read about a plethora of issues with seizing and with the lack of future accessibility in this area we would like to look at some changes.

Focusing on eliminating the threat of water back-flow we’re wondering if installing an anti siphon setup in the lazarette is the right move for us. Our engines are just below the waterline, go to a water-lift in the aft cabin and then exit the vessel through the lazarette (obviously) with some old check valves in the way (that we’d like to remove). The exhaust hose runs right along the waterline so that leaves to some ambiguity for us as to our options; any help is appreciated.

If we can install some anti siphon valves that would be the easiest option but we’re open to whatever gets it done right.

Based on some diagrams I’ve researched this seems like a viable option but I know a lot more people have more experience than we do with these systems. Again, Any input is appreciated!

I’ll attach some photos so show the lazarette to show the ample room for an anti siphon option. The water tanks we’re replacing can be modified to work around this hypothetical exhaust system.

Any issues we should be looking at or any reason we shouldn’t do this?

Thank you immensely!

 

[albinalaska]

We can, of course, just remove the check valves and add flappers on the new exhaust transom fittings but would the water lift mufflers be able to do the sufficient lifting for stopping the water from back flowing into our old engines?

Thanks!

 

[Hippocampus]

Had a problem with back pressure on a prior boat. There was extra exhaust hose placed in a loop in the bottom of the lazerette. Also run wasn’t straight and curved around other things. Total hose length was too long and due to loops water collected in the portions under the WL. That wasn’t a problem once the engine was going. Nor was there any problem with water getting back to the engine. But the added back pressure from the long run and sections with water in them was a problem with starting the engine. She would start once you blew enough air through it but that’s extra work for the starter. Took out all the extra exhaust hose although it meant moving a few things. Engine started immediately regardless of how long it sat beforehand.
So when you do this suggest figure out the shortest run possible with the least likelihood of a bunch of water sitting in the run when the engine isn’t running.

 

[mvweebles]

Attached link to Northern Lights applies to any wet exhaust install.

https://www.northern-lights.com/media/PDFs/misc_pdfs/dont_drown_me.pdf

I'm having a hard time understanding your current layout so won't comment specifically, but putting the high exhaust loop ("gooseneck" in your diagram) that far aft creates a sizeable reservoir of water. Diagrams on the extracted JPG from the Northern Lights article essentially moves the gooseneck forward, preferably right out of the lift muffler. I use SS exhaust tubing pre-bent into a 180

https://www.summitracing.com/parts/sum-622126

There should be a siphon break between the raw water pump and where it enters the exhaust system if exhaust is at or below waterline (Diagram #2 on attached pic). Guessing this applies to your setup.

Peter

 

[Hippocampus]

As always Peter says in a few words what I say in many. Too much water sitting in the system causes troubles.

 

[Keysdisease]

Forget the anti-syphon valve, do something like what's pictured from Northern Lights, #1 or #3. The intent is to get some portion of the exhaust run 18" above the waterline.

The closer this 18" is to the engine is best, so if you have room in your engine space to install the lift there and come up 18" above WL in the ER, that would be best. Because you mention the lift is in the aft cabin I assume your ER is chock full w no space. Maybe replace the exhaust run from riser to lift muffler and reinstall the lift in the lazarette. Then go up 18" above WL and back down to the thru hull.

The reason the lift in the ER is best is because in order to back flood the run from the transom to the lift has to fill up first, then it has to go uphill 18" and then fill your lift muffler and hose to the riser.

Moving the lift to the lazarette just makes things simpler with fewer connections and elbows. As mentioned backpressure is the enemy, and every turn and lift adds just a little more BP. The straightest run with the fewest turns, or sweeping turns, will create the least amount of BP.

Lastly, as mentioned, a flapper over the exhaust on the transom is a check valve, and is easy and inexpensive.

Back flooding happens under a very narrow set of conditions. Would (almost, never say never) never happen at anchor or in a well protected marina or dock. But, if tied up to an exposed dock on a nice day, and a thunderstorm happens along, the wind increases, you get some wave action, your transom is pointed into the wind, and water starts to fill the exhaust run. water goes in by wave action faster than it goes out by gravity and eventually everything fills up. Just one example. I used to keep my boat on canal open to a fairly wide section of the ICW. Always kept her docked with the bow pointed out the canal.

$0.02

 

[mvweebles]

OP - what type of engine do you have? Is the manifold fresh or raw water cooled? Maybe a picture of the engine in the engine room with approx waterline indicated. Picture of existing water injection setup into exhaust system, and run to lift muffler.

Marine exhaust systems are tricky. A frequent question on forums like this is "how long will Brand X diesel last?" Tough to say because so few rack up enough hours and run the gauntlets that kill an engine prematurely - culprit #1 is compromised exhaust system. I can dispel two myths though: first, just because it's rum for 20-years doesn't mean it's a proper design and will continue. Secondly, you cannot assume the builder did it right. There are more than a few builders who have chronic exhaust failures on generators due to poor exhaust installations.

Finally, I found it extremely difficult to get sensible advice on my exhaust system not because there aren't knowledgeable contributors, but because it's almost impossible take all aspects into consideration without a physical inspection of the boat in situ. Also, unless a marine mechanic is an avid cruiser or has rebuilt some blown motors due to exhaust issues, they are not always qualified to advise on exhaust routing and simply default to how the builder did it.

Good luck.

Peter

 

[PM]

Is it broken? If not, why fix it?

pete

 

[JDCAVE]

Worth contacting Tony Athens of Seaboard Marine. One of the more knowledgeable people on lift muffler systems. He will fabricate to meet your needs. Highly regarded I think by many on this forum.

https://www.sbmar.com/about-seaboard-marine/tony-athens/

My thoughts on your proposed work in the Lazarette: I don’t see how this solves your problems. I think all refinements to this need to be at the engine rather than down the line. Your exhaust elbow should be considered first together with the configuration of your siphon check valve.

Jim

 

[C lectric]

I will strongly second the contact of Seaboard Marine, Tony Athens owner.
He has posted a huge amount of info on his site about exhaust systems among many other subjects.
From your dwg/sketch I think you are going down the wrong road.
Do some reading and contact them.

 

[albinalaska]

Is it broken? If not, why fix it?

pete

I can certainly understand that sentiment but we aren’t sure it is working at all. During our trip up the inside passage we had maybe 20-40 gallons of saltwater on the port side under the fuel tank and under the engine that would eventually work its way down into the bilge. We’d empty it out every couple days but it would continue to seep in. We’ve yet to lock in on the exact culprit. The water lift muffler does not match the starboard side (stbd at least has a loop) and now having located the check valve and observed its condition believe it’s definitely a candidate for being seized possibly causing the water issue. So we need to do something.

 

[albinalaska]

Thanks for the replies. I’m not committed to any particular way of doing things so the insight you’re providing is very much appreciated.

My understanding of wet exhaust systems is limited so I’ll looking to the resources provided and see what comes of it.

Our generator was a piece of rust before we tossed it out of the engine room, (the 1.5” pvc pipe {in port photo above} is spliced into the exhaust and bypasses the lift muffler and goes into the engine room where it was leaking in salt water for who knows how many previous owners) our webasto heater is also a ball of rust- there’s a small but concerning tapping sound on our port engine (I have audio samples from a couple years ago when we last started her up) there’s just too many signs of water intrusion so we want to do this right or at least do what we can.

I’ll be at the boat tomorrow and will try to get a 3D scan if I can or at least a laser level in some photos for waterline reference against the components of the exhaust system.

The boat hasn’t sank after 40+ years so it might seem strange to dig in now but we’ve come this far and don’t want to have to come back and do it right later.

I’ll submit new photos when possible. Thanks again!

 

[twistedtree]

Wait a minute, you have water accumulating in the boat? That's something leaking, not necessarily a poor exhaust design. A poor exhaust design will result in water flooding the engine, not the engine room. Or if it does flood the engine room, the engine will be so far gone before that happens...


I think you are on the wrong track here focusing on the exhaust design. You have a leak, so find the leak. It might be the exhaust, but it's something broken, not necessarily a bad design.

 

[mvweebles]

Wait a minute, you have water accumulating in the boat? That's something leaking, not necessarily a poor exhaust design. A poor exhaust design will result in water flooding the engine, not the engine room. Or if it does flood the engine room, the engine will be so far gone before that happens...


I think you are on the wrong track here focusing on the exhaust design. You have a leak, so find the leak. It might be the exhaust, but it's something broken, not necessarily a bad design.

Agreed. I love these peel-back-the-onion threads that start one olace, then a key data point emerges that causes a hard turn in a different direction. "20-40 gals ever couple days" is not an inconsequential amount of water.

I'll be more blunt: OP, your first and only task is to find the leak. Nothing else matters until you do. You could have two co-incident events (leak plus exhaust), or they could be related somehow. Sounds like your original theory was the check valve was leaking which is unlikely but possible I suppose. Finding the source of 20-40 gals of water should not be too hard - see if you can isolate to only when engine is running, only when boat is underway, etc. Leaks are sneaky and deceptive - where they manifest is not often where they originate.

That said, your exhaust system is suspect. Honestly it smacks of DIY-kluge, Your disparate lift mufflers are odd indeed. What to do? Personally, I find it hard to advise on stuff like this without a better view of the entire system which is tough even with photos. Sketches help. I'm a skilled DIY-er but not an expert. Because exhaust lift, tubing and hose takes up so much space, it's hard to advise how to run it without actually seeing the available space. If you have access to a reliable and experienced marine diesel mechanic, you may want to spend the money on him to advise.

But figure out the leak first. And do check your exhaust mixing elbows for rust (best to see inside, but you may be able to get s general feel by minimally removing the raw water feed to see if the barbed nipple is wasted). Sounds like your boat has sat unloved for a while.

Peter

 

[albinalaska]

Wait a minute, you have water accumulating in the boat? That's something leaking, not necessarily a poor exhaust design. A poor exhaust design will result in water flooding the engine, not the engine room. Or if it does flood the engine room, the engine will be so far gone before that happens...


I think you are on the wrong track here focusing on the exhaust design. You have a leak, so find the leak. It might be the exhaust, but it's something broken, not necessarily a bad design.

Thanks for the insight! I wasn't aware of how back-flow would present itself in our Lehman 120's so that is helpful information. There are several significant issues we are resolving regarding the water intrusion. The exhaust system is merely one aspect that I've included in this post. I'm not attached to modifying the design (as the current design has worked for 40+ years) I just can see clear issues at hand which has made me suspect several culprits. Since we're digging into the boat so significantly I just don't want to ignore something or overlook something simply because of my lack of understanding.

To your question: Yes, we have/had water accumulation in the boat. On our trip up the Inside Passage in 2020 we observed maybe 50-60 gallons over the course of 11 days in the bilge. Beautiful calm seas the entire way. Queen Charolette handed it to us pretty good though. But once home and after we bilged it all out and posted up at the dock in our hometown for a couple weeks I would have to go pretty much every 3-4 days to bilge out 2-5 gallons of water to keep the bilge empty. This continued until we hauled the damn thing out where we've been for the past 2.5 years. To confuse everyone further: We're on the hard with our boat shrink wrapped (the shrink did partially fail and over the summer months and was left partially uncovered for about 6-8 months) but I just took 150 gallons of water out of the bilge. Likely culprit is intrusion through the starboard side wiring harness from the upper help which drops directly down into the engine room. That is much easier to seal in and deal with even after we're back in the water but while we're digging into all the other systems we simply don't want to overlook or ignore something that we don't understand. I want to explore every possible option until I can account for the water on the outboard port side under the fuel tanks and inboard of that under the port engine.

Even for my basic understanding of exhaust systems the design seems flawed in the angles out of the exhaust elbow and with the mismatched lift mufflers I'm quite sure anyone who owns a boat would start scratching their head.

We have a fun little winter gale here today so I wasn't able to get to the boat to get photos or measurements but that is on my to-do list asap.

Again, thank you greatly the for the insight!

Kyle

 

[albinalaska]

Agreed. I love these peel-back-the-onion threads that start one olace, then a key data point emerges that causes a hard turn in a different direction. "20-40 gals ever couple days" is not an inconsequential amount of water.

I'll be more blunt: OP, your first and only task is to find the leak. Nothing else matters until you do. You could have two co-incident events (leak plus exhaust), or they could be related somehow. Sounds like your original theory was the check valve was leaking which is unlikely but possible I suppose. Finding the source of 20-40 gals of water should not be too hard - see if you can isolate to only when engine is running, only when boat is underway, etc. Leaks are sneaky and deceptive - where they manifest is not often where they originate.

That said, your exhaust system is suspect. Honestly it smacks of DIY-kluge, Your disparate lift mufflers are odd indeed. What to do? Personally, I find it hard to advise on stuff like this without a better view of the entire system which is tough even with photos. Sketches help. I'm a skilled DIY-er but not an expert. Because exhaust lift, tubing and hose takes up so much space, it's hard to advise how to run it without actually seeing the available space. If you have access to a reliable and experienced marine diesel mechanic, you may want to spend the money on him to advise.

But figure out the leak first. And do check your exhaust mixing elbows for rust (best to see inside, but you may be able to get s general feel by minimally removing the raw water feed to see if the barbed nipple is wasted). Sounds like your boat has sat unloved for a while.

Peter

The exhaust elbow on the port side does show signs of rust from what I could tell with a quick glance. The refit projects haven' taken us into the engine room yet- but I will remove it and investigate it further for sure! Thanks for your input! I do have professional resources here in town for but as it could be a great many months to get the help the forum seems like the next best thing.

Thanks again!

 

[Hippocampus]

Mixing elbows rust from the inside out. What the the external appearance is gives little information. Last boat had a yanmar 80hp with wet exhaust. Their mixing elbows suck imho. The inside rotted out sufficiently that it would bend a bit with a strong firm thumb. No leak either. Outside looked perfect. Had Hinckley build me one in ss. Lasted 7 years and going strong when boat sold.
Unfortunately if the elbow is a concern only way to check it out is to take it off and look inside. If replacing it unfortunately sometimes a custom one will end up being cheaper in the long run.

Does your boat’s bilge fill when running?still?both? Cause will vary depending upon that answer. If when still or both don’t relaunch until you sort it out. A careful look see and the toilet paper trick will let you know.

 

[twistedtree]

I'd set the whole exhaust question aside for now. If the boat is filling up with water when hauled and on the hard, I'd address that first. Perhaps the solution to that problem will also explain where the water was coming from while underway. Right now it doesn't sound like you can identify any specific exhaust problem, so why are you trying to fix it? And I wouldn't get too excited about the different mufflers. Exhaust runs are often different for port and stbd engines, and the different mufflers may be nothing more than that.

 

[Xlantic]

Kyle, that's a lot of water coming from somewhere. I am surprised you are not able to see it coming in.

Have you looked at the shaft logs drip rates while underway?

The lift mufflers seem to be plastic or fibreglass. Is there a component in the wet exhaust system that is metal, could have corroded and is leaking?

 

[Northern Spy]

I have more or less the Vetus system that you have attached, except for the muffler. I had to redo my whole exhaust when I repowered, as I went from a normally aspirated 45hp to a turbo charged 75hp. Big difference in exhaust velocity.

I did reinstall a Vetus gooseneck, albeit a much larger one. Is it necessary? Probably not as it is not a sailing vessel which has the risk of backfill in a seaway with the engine off. But I do know that I am protected from a wave slap (or slaps) from a wave or wake action at dock or anchor in some of the remote places one gets caught out in here in coastal BC. Yes, I have a transom flapper too. The gooseneck makes my exhaust very quiet (along with the turbo).

If you are still interested in redoing your exhaust system, there are several good sources available for design. Don Casey's book, This Old Boat has a chapter on it. There was a magazine article from Good Old Boat, I subscribed to back in the day, that is found here:
https://goodoldboat.com/cool-quiet-and-trouble-free-exhaust/

I'm sure I got some info from an old Boatbuilder magazine too. (I loved those.)

Dave Gerr has some good stuff in his books. Nigel Calder has a few good diagrams in Marine Diesel Engines, and maybe more. I keep most of my Gerr and Calder books down on the boat, so I can't give you titles now.

Also know that the quality and variety of good quality marine wet-exhaust components is much better than what came with your boat originally. I doubt much (any?) engineering or calculations went into the original design, so there is always room to improve instead of replacement of existing components.

I'm happy with how mine came out. It's quiet, runs cool, can't backflow, has ample reserve capacity for engine cranking, and meets the engine manufacturer back pressure requirements (calculated, not measured).

Have fun.

 

[Northern Spy]

To your question: Yes, we have/had water accumulation in the boat. On our trip up the Inside Passage in 2020 we observed maybe 50-60 gallons over the course of 11 days in the bilge. Beautiful calm seas the entire way. Queen Charolette handed it to us pretty good though. But once home and after we bilged it all out and posted up at the dock in our hometown for a couple weeks I would have to go pretty much every 3-4 days to bilge out 2-5 gallons of water to keep the bilge empty. This continued until we hauled the damn thing out where we've been for the past 2.5 years. To confuse everyone further: We're on the hard with our boat shrink wrapped (the shrink did partially fail and over the summer months and was left partially uncovered for about 6-8 months) but I just took 150 gallons of water out of the bilge. Likely culprit is intrusion through the starboard side wiring harness from the upper help which drops directly down into the engine room.

Yup, SE Alaska gets a bit of rain.

For the record, my main bilge collection was rain until I found and repaired the leaks. Mine was a seam where the pilothouse met the cabin at the deck joint. Bugger to find.

Obviously, check your stuffing boxes and packing too.

 

[albinalaska]

As I’ve been examining the exhaust system in place I’m wondering if there are any guidelines with how far back the check valve should/could be placed.

In researching replacement ideas it seems like the major pitfall for check valves is the tendency for them to seize in the open or closed position. Also accessibility is usually difficult which can make them impossible to maintain regularly.

Speaking of: How often is a “regular”? When should I be checking these moving forward? The current(old) ones don’t seem like they’ve been checked in decades.

Also, If I were to keep the current iteration of our exhaust system and replace the check valves on our wet exhaust can I not move the new ones … say 20-25” forward?

This will get the check valves out from under the water tanks in the lazarette (that make maintenance and inspection of the check valves absolutely impossible without removing the tanks) and into the main aft cabin where the exhaust hose hides neatly under the bunk on the port side and neatly within the confines of a cabinet on the stbd side. Then I wouldn’t have to disassemble the entire lazarette to inspect.

Just exploring options!

As always, thanks!

 

[Keysdisease]

External check valve, simple, inexpensive, rarely gets stuck

 

[twistedtree]

Were you able to figure out where/how all the water was getting into the boat?


I'm still not convinced there is really anything that needs to be fixed in the exhaust. There is nothing to suggest any problem, once it became clear that all the water intrusion was into the boat, not into the engine. And especially so when we learned that the boat is filling with water even while hauled and on the hard. That's not coming from the exhaust.


I think if you still want an evaluation of your exhaust, you need to draw an elevation drawing showing how it's currently build. Show the water line, the engine and especially the exhaust point on the engine, the water injection point into the exhaust, the mufflers, hose run from the muffler to where it exits the boat, plus the location and make/model of the check valve. The drawing should look like the one you posted a couple of posts ago, but obviously specific to your boat build.