Trawler Forum

Trawler Forum (https://www.trawlerforum.com/forums/)
-   Power Systems (https://www.trawlerforum.com/forums/s6/)
-   -   Wet Exhaust BIG NO-NO (https://www.trawlerforum.com/forums/s6/wet-exhaust-big-no-no-61896.html)

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.


All times are GMT -5. The time now is 01:38 PM.

Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2022, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012