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Alaskan Sea-Duction 01-17-2022 06:04 PM

Wet Exhaust BIG NO-NO
 
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:

Comodave 01-17-2022 06:35 PM

Let me know, I have no problem drilling holes in your boat…

Alaskan Sea-Duction 01-17-2022 06:52 PM

Quote:

Originally Posted by Comodave (Post 1069302)
Let me know, I have no problem drilling holes in your boat…

Very funny. Be nice!! :eek::D:dance:

Comodave 01-17-2022 06:55 PM

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…

rslifkin 01-17-2022 07:00 PM

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.

Alaskan Sea-Duction 01-17-2022 07:21 PM

Quote:

Originally Posted by Comodave (Post 1069313)
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…

Thanks.

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

Alaskan Sea-Duction 01-17-2022 07:22 PM

Quote:

Originally Posted by rslifkin (Post 1069314)
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.

They did tell me I could keep the original set up, but would void the warranty.

chriscritchett 01-17-2022 07:29 PM

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.

rgano 01-17-2022 07:50 PM

Quote:

Originally Posted by Comodave (Post 1069313)
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…

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. :)

Comodave 01-17-2022 07:52 PM

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.

O C Diver 01-17-2022 08:23 PM

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

chriscritchett 01-17-2022 08:55 PM

‘If not done correctly’ gives a bad name to so many otherwise reasonable ideas.

ofer 01-17-2022 08:57 PM

Quote:

Originally Posted by Alaskan Sea-Duction (Post 1069322)
Thanks.

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

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.

Soo-Valley 01-17-2022 09:24 PM

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.

Keysdisease 01-17-2022 09:24 PM

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:

Alaskan Sea-Duction 01-17-2022 11:57 PM

Quote:

Originally Posted by Soo-Valley (Post 1069361)
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.

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.

IRENE 01-18-2022 06:32 AM

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,

twistedtree 01-18-2022 07:19 AM

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.

rslifkin 01-18-2022 07:42 AM

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.

Ken E. 01-18-2022 11:15 AM

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.

Alaskan Sea-Duction 01-18-2022 12:09 PM

Quote:

Originally Posted by twistedtree (Post 1069424)

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.

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.

Quote:

Originally Posted by Ken E. (Post 1069493)
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.

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.

Soo-Valley 01-18-2022 12:21 PM

Quote:

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.
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.

ancora 01-18-2022 12:24 PM

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.

Alaskan Sea-Duction 01-18-2022 01:11 PM

Quote:

Originally Posted by Soo-Valley (Post 1069519)
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.

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:

Soo-Valley 01-18-2022 02:06 PM

Quote:

Originally Posted by Alaskan Sea-Duction (Post 1069529)
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:

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.

Alaskan Sea-Duction 01-18-2022 04:37 PM

Quote:

Originally Posted by Soo-Valley (Post 1069544)
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.

Thanks

Keysdisease 01-18-2022 07:14 PM

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:



Quote:

Originally Posted by Alaskan Sea-Duction (Post 1069512)
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.


Alaskan Sea-Duction 01-18-2022 08:45 PM

Quote:

Originally Posted by Keysdisease (Post 1069635)
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:

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.

Keysdisease 01-19-2022 07:33 AM

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:

Alaskan Sea-Duction 01-19-2022 01:45 PM

Thanks

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

Keysdisease 01-19-2022 06:21 PM

That does not mean the seal well. Its very easy to determine if treating the hatches is worthwhile. Once the new unit is installed close the hatches and use masking tape to seal them. Note any difference, make decision based on observations. If you have a Db meter on your phone, use it. Be sure ambient noise is same/same before/after

If you do gasket install on the hatch so it contacts the inside hump of the gutter. Less chance of damage on the hatch. Some clay in the right spot when mashed by the hatch will give an indication of how thick a gasket you may need

:socool:


Quote:

Originally Posted by Alaskan Sea-Duction (Post 1069886)
Thanks

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


Alaskan Sea-Duction 01-19-2022 08:13 PM

Quote:

Originally Posted by Keysdisease (Post 1070003)
That does not mean the seal well. Its very easy to determine if treating the hatches is worthwhile. Once the new unit is installed close the hatches and use masking tape to seal them. Note any difference, make decision based on observations. If you have a Db meter on your phone, use it. Be sure ambient noise is same/same before/after

If you do gasket install on the hatch so it contacts the inside hump of the gutter. Less chance of damage on the hatch. Some clay in the right spot when mashed by the hatch will give an indication of how thick a gasket you may need

:socool:

Thank you.

Cleanslate 01-20-2022 07:30 PM

Wouldn’t just installing a Centek Vernalift in the generator exhaust line a foot or three away from the gen exhaust discharge solve your problem? It should .
No need to drill a hole in the boat for a new exhaust.
Most generators have them when they are at or below the waterline just off to the side in the bilge. That prevents the backflow of water into your generator..

Soo-Valley 01-20-2022 08:20 PM

Warranty is the reason for the change

Alaskan Sea-Duction 01-20-2022 10:51 PM

Quote:

Originally Posted by Soo-Valley (Post 1070467)
Warranty is the reason for the change

Yep

Keysdisease 01-21-2022 08:20 AM

Just about every marine generator with wet exhaust has a lift muffler installed. They will "reduce" or "slow" the chances of backflood, but under the right conditions (the same conditions for any backflood) they can fill with water and then up to the riser and on to the turbo and valves.
Lift mufflers start their day partially filled with water that flows from the riser when you shut down and there's no exhaust gas to "lift" it out.

A separator has an actual "plate" inside that stops the water from staying mixed with the exhaust gas and the water drops to exit through the Seps drain. Any water coming back up the exhaust gas piping will drop through the drain before it can get past the separator and then into the lift and beyond. Installed correctly a separator will make backflooding next to impossible.

I believe ASD is replacing his trusty Onan after many years because it backflooded? I would bet a 6-pack of refreshing beverages that he had a lift muffler inline.

:socool:


Quote:

Originally Posted by Cleanslate (Post 1070445)
Wouldn’t just installing a Centek Vernalift in the generator exhaust line a foot or three away from the gen exhaust discharge solve your problem? It should .
No need to drill a hole in the boat for a new exhaust.
Most generators have them when they are at or below the waterline just off to the side in the bilge. That prevents the backflow of water into your generator..


FoxtrotCharlie 01-21-2022 11:12 AM

When we got our new Kohler 9k gennie several yrs ago, instructions said to use a separate exhaust outlet - fortunately, our boat with it's old gen had a separate exhaust outlet - we also ran a completely new exhaust line at the time.

Alaskan Sea-Duction 01-21-2022 12:28 PM

Quote:

Originally Posted by Keysdisease (Post 1070567)
Just about every marine generator with wet exhaust has a lift muffler installed. They will "reduce" or "slow" the chances of backflood, but under the right conditions (the same conditions for any backflood) they can fill with water and then up to the riser and on to the turbo and valves.

Lift mufflers start their day partially filled with water that flows from the riser when you shut down and there's no exhaust gas to "lift" it out.



A separator has an actual "plate" inside that stops the water from staying mixed with the exhaust gas and the water drops to exit through the Seps drain. Any water coming back up the exhaust gas piping will drop through the drain before it can get past the separator and then into the lift and beyond. Installed correctly a separator will make backflooding next to impossible.



I believe ASD is replacing his trusty Onan after many years because it backflooded? I would bet a 6-pack of refreshing beverages that he had a lift muffler inline.



:socool:

Yep

Cleanslate 01-21-2022 11:26 PM

Ok, interesting. Something is a miss .
Perhaps more rise between the generator and the Aqua lift ( Onan muffler / lift) could have fixed things ?
A new motor in place of the old motor (Perkins? / Onan) won’t solve the hydro lock issues .
I hope all works out .

Brooksie 01-24-2022 01:54 PM

What may work fine for years will suddenly fill your engine when anchored in a seaway. Most wet exhausts are designed with the engine running in mind under which conditions even the poorest design would usually expel its own exhaust water.

Keysdisease 01-24-2022 02:36 PM

Without any check valves or anti siphon loops any "traditional" lift muffler installation can backflood. The only exception "might" be installations where the generator is mounted way above the waterline. Some of the French catamarans for example have the generators on the bridge deck between the hulls under a cockpit seat.

What Brooksie said is very true. The typical backflood scenario is a vessel tied to a dock when the wind picks up from astern and causes a chop to hit the transom just right and push water up the generator exhaust pipe. Having a lift just slows the flood down as the lift has to fill first. The chop continues to push water up the exhaust until it starts going uphill to the turbo and/or exhaust manifold and then onto the exhaust valves.

Most docks are in protected water and a chop big enough to do this can't build. At anchor your transom is pointing away from the wind or any chop. Typically only in specific conditions like the one described can backflood happen. That's why vessels can go for years with no problem, until the planets align and the rules of fluid dynamics cause water to run uphill and ruin your day.

Transom flappers and check valves can help, making your exhaust run from the lift to the transom as uphill as possible will help. A separator makes it almost impossible. Some people will put a plug in the exhaust when they leave the boat for an extended time, the properly sized inflatable fender works well for this.

:socool:


Quote:

Originally Posted by Cleanslate (Post 1070812)
Ok, interesting. Something is a miss .
Perhaps more rise between the generator and the Aqua lift ( Onan muffler / lift) could have fixed things ?
A new motor in place of the old motor (Perkins? / Onan) won’t solve the hydro lock issues .
I hope all works out .


woodlord 01-24-2022 03:11 PM

That will make exhaust louder above water mine is down just before the bottom
 
[QU=IRENE;1069418]Tom,
Mine is 1 foot below waterline northern lights and very quiet Evan when tied up next to someone on that side
Dana
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,[/QUOTE]

Steve DAntonio 01-24-2022 04:28 PM

ABYC Standards prohibit sharing of exhaust discharges, for obvious reasons, water or gas could migrate into a non-running engine.

Steve DAntonio 01-24-2022 04:35 PM

This doc, from NL, is pretty clear, and better than most other genset and small engine guidance on this subject. https://www.northern-lights.com/medi...t_drown_me.pdf

Alaskan Sea-Duction 01-24-2022 05:36 PM

Quote:

Originally Posted by Steve DAntonio (Post 1071432)
ABYC Standards prohibit sharing of exhaust discharges, for obvious reasons, water or gas could migrate into a non-running engine.

Well I would say this "suggestion" was not around in the 80's, early 90's.

dathompson 01-24-2022 05:40 PM

Quote:

Originally Posted by Ken E. (Post 1069493)
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.

Ken, I run my NL 6kw with the service side panel removed. I can't tell any difference in the noise level.

Alaskan Sea-Duction 01-24-2022 05:42 PM

Quote:

Originally Posted by Steve DAntonio (Post 1071437)
This doc, from NL, is pretty clear, and better than most other genset and small engine guidance on this subject. https://www.northern-lights.com/medi...t_drown_me.pdf

Great point. Great information and coincide with what the mechanic stated. Thanks.

O C Diver 01-24-2022 07:06 PM

Quote:

Originally Posted by Steve DAntonio (Post 1071432)
ABYC Standards prohibit sharing of exhaust discharges, for obvious reasons, water or gas could migrate into a non-running engine.

I've seen a fair number of 40' to 60' sport fishing boats with shared exhausts. We're talking North Carolina
million dollar boats. Many are probably within a foot of the hull in the exhaust tube. My 2002 Cherubini was setup that way but with a side exhaust. Wonder when ABYC came up with that rule.

Ted

Parrothedd 01-24-2022 09:11 PM

Generator exhaust
 
By all means, pay the extra money for the air/water separator. It makes your boat silent in anchorages.

Steve DAntonio 01-25-2022 11:47 AM

Quote:

Originally Posted by Alaskan Sea-Duction (Post 1071468)
Well I would say this "suggestion" was not around in the 80's, early 90's.

I could find out when it was adopted, that's all part of the ABYC Standards record, but I'll agree the proliferation and acceptance of ABYC Standards didn't begin to occur until early 2000s. Still, it's a rarity even on older vessels, and yet I encounter it from time to time even on new vessels.


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