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08-17-2014, 09:14 PM
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#1
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Veteran Member
City: WYC, Port Whitby, Ontario
Vessel Name: Bonaventure
Vessel Model: Cheer Men PT41 Europa
Join Date: May 2014
Posts: 94
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Best way to quiet my Lehman 120 Exhaust
Hi All:
So I have a pair of 120 Ford Lehmans which currently have a very "droning" exhaust note at most any RPM.
From my engines there is about 6ft of 3.5" wet exhaust hose going to Stainless lift type mufflers which then slope very gradually downhill via more 3.5" hose to straight outlets at the stern.
I bought a Vetus DMP90 muffler and installed it inline on my stbd engine (to see what if any difference it made) and (despite Vetus assurances) it made absolutely no difference at all. The "muffler" would need significantly more water flow (at least 2-3 times IMHO) to make any real difference.
I have ordered and am planning on trying a Vetus LT90 water lift right at the stern on the port engine in a few days in hopes that the mixing right at the transom may make a difference.
Wondering what (if anything) others have done to quiet the exhaust note.
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08-17-2014, 09:32 PM
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#2
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Guru
City: Sarasota/Ft. Lauderdale
Join Date: Apr 2014
Posts: 5,438
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There used to be a company, who's name escapes me at the moment, that made transom mounted exhaust outlet diverters out of heavy rubber that directed your exhaust down into the water. If they are still around you could try those.
Or make one yourself out of hose and a fiberglass 90 deg. fitting.
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08-17-2014, 09:54 PM
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#3
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Technical Guru
City: Wilmington, NC
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 6,194
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Are you sure the noise is coming from the exhaust? Non turbo diesels have a lot of noise coming from the air intake and that is fixable.
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08-17-2014, 11:14 PM
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#4
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Guru
City: Sarasota/Ft. Lauderdale
Join Date: Apr 2014
Posts: 5,438
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That sound is pretty common to Lehman's. If it changes to a hollow sound it means you've lost or are loosing raw water flow.
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08-18-2014, 12:15 AM
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#5
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Hospitality Officer
City: Pittwater
Vessel Name: Sarawana
Vessel Model: IG 36 Quad Cabin
Join Date: Sep 2010
Posts: 1,897
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I'm having trouble visualising( what's the audio description of visualising) a droning exhaust note over the shaking and rattling the old girl makes when I start her up.
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08-18-2014, 01:48 AM
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#6
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Guru
City: Sydney
Vessel Name: Sojourn
Vessel Model: Integrity 386
Join Date: Oct 2011
Posts: 13,333
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Quote:
Originally Posted by Rduval
...I have a pair of 120 Ford Lehmans which currently have a very "droning" exhaust note at most any RPM...
Wondering what (if anything) others have done to quiet the exhaust note.
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Only thing I can think of is shutting them down. They`re Lehmans.
__________________
BruceK
2005 Integrity 386 "Sojourn"
Sydney Australia
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08-18-2014, 01:57 AM
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#7
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Scraping Paint
City: -
Join Date: Oct 2007
Posts: 13,745
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Our two FL120s make a fair amount of mechanical noise inside the boat. But there is no exhaust noise at all unless one stands on the aft deck right at the transom. We have a custom exhaust system (see photo) with fiberglass lift mufflers feeding the stock exhaust hoses. The mufflers, which have drain fittings at the bottom, and the fiberglass top elbows, were made specifically for our engines and boat by an exhaust shop in Bellingham. The diesel shop we use made the platforms the mufflers sit on and installed the systems using water-cooled manifold elbows from American Diesel. The exhausts themselves are pretty quiet at the transom.
A nice feature of this system is everything but the upper elbows are below the rear of the manifold. So no water can make its way back through the system and into the manifold. This was not the case when we bought the boat. The systems on the boat when we acquired it had the mufflers suspended from the engine room overhead.
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08-18-2014, 02:27 AM
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#8
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Hospitality Officer
City: Pittwater
Vessel Name: Sarawana
Vessel Model: IG 36 Quad Cabin
Join Date: Sep 2010
Posts: 1,897
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Quote:
Originally Posted by Marin
The systems on the boat when we acquired it had the mufflers suspended from the engine room overhead.
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Yikes! That is not good.
A couple of years ago I had the unfortunate experience of the muffler box being raised higher than the manifold, when our boat was slipped. That cost about $24,500 and six months off the water. Thank god for insurance.
By the way Marin good to see you around again.
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08-18-2014, 06:27 AM
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#9
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Senior Member
Join Date: Dec 2010
Posts: 207
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We have a 3.5" exhaust on our stbd engine and a 3" exhaust on our port engine, both 2715e Lees Marine (same engine as Lehman, different marinization). The Lehman manual calls for a 3" exhaust. The 3" exhaust on our port engine has a mellow, fairly quiet sound. The 3.5" exhaust has a throaty sound, much louder than the 3" exhaust. Perhaps your problem is the oversize exhaust and not the muffler.
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08-18-2014, 06:43 AM
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#10
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Veteran Member
City: WYC, Port Whitby, Ontario
Vessel Name: Bonaventure
Vessel Model: Cheer Men PT41 Europa
Join Date: May 2014
Posts: 94
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Quote:
Originally Posted by Capt.Bill11
That sound is pretty common to Lehman's. If it changes to a hollow sound it means you've lost or are loosing raw water flow.
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Funny you should say that Capt Bill, I'm also seeing a lot of steam in the exhaust which I'm told shouldn't be there if there is enough cooling water flow.
Impellers are new 3 months ago, raw water strainers are clear... How do I know if I'm getting enough.
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08-18-2014, 06:48 AM
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#11
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Veteran Member
City: WYC, Port Whitby, Ontario
Vessel Name: Bonaventure
Vessel Model: Cheer Men PT41 Europa
Join Date: May 2014
Posts: 94
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Quote:
Originally Posted by Ski in NC
Are you sure the noise is coming from the exhaust? Non turbo diesels have a lot of noise coming from the air intake and that is fixable.
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That's something I've thought about as well but in this case it's definitely exhaust that's the problem but I'm open to suggestions on quieting the intakes as well.
What's the solution to that? I've just got the standard coffee can type screens with foam around them at the moment.
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08-18-2014, 06:53 AM
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#12
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Veteran Member
City: WYC, Port Whitby, Ontario
Vessel Name: Bonaventure
Vessel Model: Cheer Men PT41 Europa
Join Date: May 2014
Posts: 94
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Quote:
Originally Posted by Tomas
We have a 3.5" exhaust on our stbd engine and a 3" exhaust on our port engine, both 2715e Lees Marine (same engine as Lehman, different marinization). The Lehman manual calls for a 3" exhaust. The 3" exhaust on our port engine has a mellow, fairly quiet sound. The 3.5" exhaust has a throaty sound, much louder than the 3" exhaust. Perhaps your problem is the oversize exhaust and not the muffler.
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That's something I've considered as well. It sure doesn't seem like it would need a 3.5"ID exhaust system but that's what the Lehman mixing elbow is so it's been continued all the way through.
I noticed Marin's photo of his custom exhaust that the outlet looks about half the size of the inlet. Is that that case Marin?
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08-18-2014, 07:20 AM
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#13
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Guru
City: Upstate,SC
Vessel Name: Shipoopi
Vessel Model: derilic sailboat
Join Date: May 2012
Posts: 2,884
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Could it be bad or dried out hardened engine mounts?I know that bad engine mounts can cause a drone thru the hull, that can sound like exhaust noise.
__________________
This is my signature line. There are many like it but this one is mine.
What a pain in the transom.
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08-18-2014, 07:39 AM
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#14
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Veteran Member
City: WYC, Port Whitby, Ontario
Vessel Name: Bonaventure
Vessel Model: Cheer Men PT41 Europa
Join Date: May 2014
Posts: 94
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Quote:
Originally Posted by ben2go
Could it be bad or dried out hardened engine mounts?I know that bad engine mounts can cause a drone thru the hull, that can sound like exhaust noise.
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Nope, brand new mounts that made the boat MUCH quieter overall. This is definitely the exhaust note.
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08-18-2014, 08:43 AM
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#15
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Guru
City: Concrete Washington State
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 18,743
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A 400 cu in old diesel engine is bound to be noisy. I'll bet if you had the engine suspended by magic and not touching the boat the "droning" noise would be gone. You're probably not getting the "rumrumrumrum" noise directly from the engine.
The engine shakes the boat and lots of parts of the boat shake at various frequencies and those parts in turn shake other parts at frequencies not the same as the original exciter frequency. A bulkhead may be resonant to 1100 rpm and your reduction gear provides that frequency through the propeller shaft and prop.
Whenever you have two frequencies vibrating at close to the same frequency another vibration and frequency emerge called the "beat frequency" in electronics. It's frequently a low frequency like the drumming of a twin engined boat or airplane w the engines not synced. It's usually called a "harmonic" frequency.
Look for something like a bulkhead or other flat panel that "drum". Feel all around for things other than the engine that are vibrating. It will probably feel like the vibration is coming and going. A fix is to attach something solid to that thing vibrating and not in the center is best.
Another thing to consider is the exhaust hose shaking things. Exhaust hose is frequently very stiff and will pass shaking to another boat part ... like a plywood platform that a lift muffler is attached to.
__________________
Eric
North Western Washington State USA
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08-18-2014, 08:51 AM
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#16
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Guru
City: Sarasota/Ft. Lauderdale
Join Date: Apr 2014
Posts: 5,438
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Quote:
Originally Posted by Rduval
That's something I've considered as well. It sure doesn't seem like it would need a 3.5"ID exhaust system but that's what the Lehman mixing elbow is so it's been continued all the way through.
I noticed Marin's photo of his custom exhaust that the outlet looks about half the size of the inlet. Is that that case Marin?
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It does look that way. But it shouldn't be. Might just be the way the picture makes it look. That is pretty much the standard exhaust set up on a GB.
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08-18-2014, 08:54 AM
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#17
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Guru
City: Sarasota/Ft. Lauderdale
Join Date: Apr 2014
Posts: 5,438
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Quote:
Originally Posted by Rduval
Funny you should say that Capt Bill, I'm also seeing a lot of steam in the exhaust which I'm told shouldn't be there if there is enough cooling water flow.
Impellers are new 3 months ago, raw water strainers are clear... How do I know if I'm getting enough.
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When was the last time you boiled out your coolers? And how old is you mixing elbow? Is it SS or stock steel?
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08-18-2014, 08:56 AM
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#18
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Guru
City: gulf coast
Join Date: Jun 2014
Posts: 3,440
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Many good suggestions, especially quieting the intakes. I'll add consider sound insulation under the deck. Feeling for vibrating items is a good idea. There is an app for iPhone called Db meter you can point your phone at something to see if sound is coming from there.
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08-18-2014, 08:59 AM
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#19
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Guru
City: gulf coast
Join Date: Jun 2014
Posts: 3,440
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Steam usually means insufficient water flow. Water quiets exhaust.
Is the Sind more apparent outside at the stern.
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08-18-2014, 09:12 AM
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#20
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Guru
City: Sarasota/Ft. Lauderdale
Join Date: Apr 2014
Posts: 5,438
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Call me crazy but I guessing this guy knows the difference from a sound made by vibration and the sound his exhaust is making at the transom.
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