Wet Exhaust BIG NO-NO

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Alaskan Sea-Duction

Alaskan Sea-Duction

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Joined
Jul 6, 2012
Messages
8,057
Location
USA
Vessel Name
Alaskan Sea-Duction
Vessel Make
1988 M/Y Camargue YachtFisher
After reading the install manual on my new genset I now understand why. Hydrolock. It happened twice last year.

My boat is a 1988 with twin CATS and an Onan Genset. The exhaust for the genset is piped through a wet muffler, to the exhaust of the port main engine. A big no-no it appears.

Why would the Onan be plumbed this way? The Onan install manual says the same thing!

Looks like I need a new hole in the stern of ASD!:angel:
 
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Let me know, I have no problem drilling holes in your boat…
 
It was an honest offer. I sincerely don’t mind drilling on your boat. I have done it for several friends that were nervous about drilling through the hull. I would even try to get it in the right place…
 
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In theory if the main exhaust tubes are big enough and placed where they'll never become fully submerged, then as long as the rest of the rules of good exhaust design are followed, it should be safe. That said, I'd much prefer a separate thru hull.
 
Comodave said:
It was an honest offer. I sincerely don’t mind drilling on your boat. I have done it for several friends that were nervous about drilling through the hull. I would even try to get it in the right place…
Click to expand...
Thanks.

Cook Engines in Portland is doing the week. They have a lift.
 
rslifkin said:
In theory if the main exhaust tubes are big enough and placed where they'll never become fully submerged, then as long as the rest of the rules of good exhaust design are followed, it should be safe. That said, I'd much prefer a separate thru hull.
Click to expand...
They did tell me I could keep the original set up, but would void the warranty.
 
Big no-no for other reasons as well. Best to go with the separate thru-hull, but if you were really against that, what many big sportfish do is join the gen exh run to the main engine piping just before the outlet and do a ‘pipe-within-a-pipe’ detail all the way back to essentially have 2 ‘separate’ runs share the thru-hull outlet. I’m sure if you search the inter webs you can find a picture of what I’m talking about.
But best & probably easiest to add a new hole.
 
Comodave said:
It was an honest offer. I sincerely don’t mind drilling on your boat. I have done it for several friends that were nervous about drilling through the hull. I would even try to get it in the right place…
Click to expand...

Reminds me of a funny story. I used the assistance of a looper moored at my pier for a day or two to drill a 3/8-inch hole in the bottom of my wooden hull to mount an Electro-Guard zinc. I was in the water with the gooped up bolt going up through the hull, and he was inside with a battery-operated drill. He was really nervous, but it went smoothly. Later he bragged, "I drilled a hole through Rich Gano's underwater hull with the boat in the water."

I probably would draw the line at anything larger. :)
 
I have read about putting in a transducer through the hull in the water using a bowl on the outside. Not sure I would want to try it though.
 
I like my combined exhaust. I installed the stern exhaust on my boat when doing the refit and repower. Now to be fair, I had the removed fiberglass exhaust pipe from the original motor. So the 4" exhaust from the John Deere and the 2" exhaust from the Onan combine in an 8" fiberglass exhaust pipe. One of the nice advantages of this setup is that with almost empty fuel tanks, the inside of the outlet is just below sea level at anchor. No water splash sounds while running the generator. Both the engine and generator have lift muffler systems with the generator reaching 30" above sea level and going through a silencer / water gas separator. If done correctly, they're very safe and extremely quiet.

Ted
 
Alaskan Sea-Duction said:
Thanks.

Cook Engines in Portland is doing the week. They have a lift.
Click to expand...

they did a yanmar install for me in 2011.

their website shows 2013-2022. did they go through a change?

very good installers. i would take their recommendations.
 
Tom. Is the lazerett a normal install location for the genny? I am asking due to location the current exhaust setup protects genny better for a wave surge going up the exhaust pipe as it has the length of the engine pipe. Guess a flap will be added to prevent that.
 
Another reason to not dump generator exhaust into a main is that the big pipe can act like a megaphone and increases the volume of the generator exhaust.

:facepalm:

Also, going back to my suggestion to install a separator, when installed correctly a separator makes backflooding the generator almost impossible.

:socool:
 
Soo-Valley said:
Tom. Is the lazerett a normal install location for the genny? I am asking due to location the current exhaust setup protects genny better for a wave surge going up the exhaust pipe as it has the length of the engine pipe. Guess a flap will be added to prevent that.
Click to expand...
On a 42ft Camargue it is located in the engine room. On the 48ft they place it in the cockpit. Sound shielding too..

Two 50gal fuel tanks are also in the cockpit.
 
Tom,

You probably thought about these already but some pre-caffinated ideas this morning:

Have the yard make the new hole sufficiently high so that the exhaust does not disturb the water. The blowing/bubbling/splashing could be the noisiest thing with your new set (it is with our NL 9kw). The elevated height will work nice with a Gen Sep, if you are going that route.

Take Care,
 
If practical, I would add a gensep. It eliminates any splashing water outside, and the exhaust is no louder than a dryer vent.


Have you figured out why/how the old gen got water in it? Is it just because of the shared exhaust, and do you understand how that drove water into the gen?


Obviously you want to be certain that the new gen doesn't suffer the same fate.
 
If you don't go for a gensep, try to put a small inline muffler after the waterlift, right before the thru hull. The extra volume will dampen the water pulsing and give closer to a steady stream of water coming out (which means less noise).


I also agree with getting the thru hull well above the water. Not too high if it's discharging water (noise), but high enough that it doesn't get submerged to avoid extra noises from moving water out of the way.
 
Tom, I also removed an Onan, 6kw, and replaced it with a NL 5kw. Regarding the sound shield, the shop that installed it said that the NL without the shield would be quieter than the Onan with the shield. They were right. And my location is under the salon sole, between the two engines rather than your lazarette location which is farther removed from living spaces. My gen is quiet in the salon and sounds like a sewing machine. We hardly notice it. If you deleted the shield, your access and maintenance would be easier too. I'd spring for upgraded isolation mounts instead, to get rid of any vibration. I'd also go with a separate through-hull for the exhaust and make sure they give you a 1 foot loop above the waterline.
 
twistedtree said:
Have you figured out why/how the old gen got water in it? Is it just because of the shared exhaust, and do you understand how that drove water into the gen?


Obviously you want to be certain that the new gen doesn't suffer the same fate.
Click to expand...

Yes we did. When we had beam seas and the boat would rock, it pressurized the intake hose from the through hull to the raw water pump. The intake is suppose to have a "Loop" to prevent it. Don't know if this is the way the manufacture installed it or the previous owner. We are the 3rd owners.

Ken E. said:
Tom, I also removed an Onan, 6kw, and replaced it with a NL 5kw. Regarding the sound shield, the shop that installed it said that the NL without the shield would be quieter than the Onan with the shield. They were right. And my location is under the salon sole, between the two engines rather than your lazarette location which is farther removed from living spaces. My gen is quiet in the salon and sounds like a sewing machine. We hardly notice it. If you deleted the shield, your access and maintenance would be easier too. I'd spring for upgraded isolation mounts instead, to get rid of any vibration. I'd also go with a separate through-hull for the exhaust and make sure they give you a 1 foot loop above the waterline.
Click to expand...

Being quiet is a big reason we are getting a NL. The sound shield is recommended by NL as the genset will be in the cockpit and could be exposed to some water dripping down from the deck.
 
Yes we did. When we had beam seas and the boat would rock, it pressurized the intake hose from the through hull to the raw water pump. The intake is suppose to have a "Loop" to prevent it.
Click to expand...
A loop without an anti siphon break will not stop a surge IMO.
I was focusing on the exhaust, did not think about intake.
Thus why I asked if the install location was normal, so close to forced water injestation.
 
I bought a Westerbeke 5 kw and installed it myself. Against all advice, I tapped off the the salt water toilet through hull. That was twenty two year ago, and it's still running. Also, against all advice, I removed the shower sump pump and plumbed the shower water into the forward sump pit, to be removed by the bilge pump. That was also twenty two years ago, with no problems.
 
Soo-Valley said:
A loop without an anti siphon break will not stop a surge IMO.
I was focusing on the exhaust, did not think about intake.
Thus why I asked if the install location was normal, so close to forced water injestation.
Click to expand...

A few years ago I installed an exhaust check valve between the wet muffler and the the main exhaust. So no back water from the exhaust. However, no siphoning loop on the intake or exhaust. Genset sits at waterline in the cockpit.:eek:
 
Alaskan Sea-Duction said:
A few years ago I installed an exhaust check valve between the wet muffler and the the main exhaust. So no back water from the exhaust. However, no siphoning loop on the intake or exhaust. Genset sits at waterline in the cockpit.:eek:
Click to expand...

The exhaust into the engine line probably entered at top thus less chance of backflow.
If by a loop you meant up as high as possible then back down before attaches to genny, I agree it may help. My thoughts are the intake should be more forward in more stable outside water level.
Your boat probably digs a big hole at the stern putting the genny well below water line inviting a backflow into it with a wave or sudden stop.
Practice closing thru hull when not in use.
 
Soo-Valley said:
The exhaust into the engine line probably entered at top thus less chance of backflow.

If by a loop you meant up as high as possible then back down before attaches to genny, I agree it may help. My thoughts are the intake should be more forward in more stable outside water level.

Your boat probably digs a big hole at the stern putting the genny well below water line inviting a backflow into it with a wave or sudden stop.

Practice closing thru hull when not in use.
Click to expand...
Thanks
 
As mentioned spring (no pun) for the secondary isolation. You're already getting the sound shield, and if you get a GenSep you will have the Trifecta of quiet plus backflood protection.

The new NL without a soundshield may be quieter than the old Onan with a soundshield, but the new NL will be quieter with the soundshield than without.

The way the Separator prevents backflooding is that any water that comes up the gas outlet will just naturally route through the drain of the separator. Except for "impossible" being possible when it comes to boats, a Gensep is as close to impossible as you can get, with the added benefit of a much quieter installation.

$0.02 :socool:



Alaskan Sea-Duction said:
Being quiet is a big reason we are getting a NL. The sound shield is recommended by NL as the genset will be in the cockpit and could be exposed to some water dripping down from the deck.
Click to expand...
 
Keysdisease said:
As mentioned spring (no pun) for the secondary isolation. You're already getting the sound shield, and if you get a GenSep you will have the Trifecta of quiet plus backflood protection.



The new NL without a soundshield may be quieter than the old Onan with a soundshield, but the new NL will be quieter with the soundshield than without.



The way the Separator prevents backflooding is that any water that comes up the gas outlet will just naturally route through the drain of the separator. Except for "impossible" being possible when it comes to boats, a Gensep is as close to impossible as you can get, with the added benefit of a much quieter installation.



$0.02 :socool:
Click to expand...
Thanks. The old Onan was quiet and once you were 50 feet from the stern you couldn't hear it at all. Based on your observations I am excited to see how quiet it will be.
 
Gasketing the cockpit hatches and how the compartment gets air for combustion are two other things critical for noise reduction.

Leaky (noise leaky) hatches can account for 5+ Dba of noise. Also how does air get into that compartment? If there are vents on the transom, hullside, some sort of vent trunk into the engine room, those air path treatments will be quiet. If there is a vent in the cockpit it will be noisier. A simple "shoebox" baffle over a cockpit vent will help. Look at the air intake for your new NL enclosure, they utilize that type baffle. Basically breaks the "line of sight" and tortures and absorbs the noise path without restricting air flow

:socool:
 
Thanks

The 2 cockpit doors are heavy and have a gutter around each door. Any water runs down the gutter and pipped overboard.
 
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