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Old 07-02-2012, 10:36 PM   #1
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Exhaust

My 4-154 Diesel we have converted to a wet system i was at the boat yard yesterday. And 2 of the trawlers had a turn down on the exhuast putting it below the water line ? What if any advantage is this ? Sound or Smut ? i ask one owner who told me the P/O had installed it.
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Old 07-03-2012, 12:50 AM   #2
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Under water or at water line exhaust are usually quieter.I don't know of any other advantages, except stopping carbon monoxide from building up, in or around the boat.I prefer above water exhaust.Under water, or at water line, exhaust can sink a boat real quick,if everything isn't kept in check with the exhaust and thru hull.
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Old 07-10-2012, 12:08 AM   #3
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My entire system is above water and dumps about 2 inches above the water line, These turn downs were on a above the water line but the turn downs were 90's that turned down and ended below the water line. my question is back preasure or other issues ? i have only seen this on a few of these on trawlers. On my dads power boat the pipes dumped out the bottom of the boat about 2 inches from the rear but that was 500hp i have 70 not sure if it is a good idea or something i should just forget.
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Old 07-10-2012, 02:35 AM   #4
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I've seen underwater exhausts, partially underwater exhausts, and above the waterline exhausts. But I've not yet seen an above water exhaust that was turned down to exit under the water.

Of course one question would be when the boat is actually underway is the turned down exhaust still exiting underwater? It might not be.

The guesses of noise reduction or soot reduction (if it's a sooty exhaust) would seem to make the most sense. My inclination would be not to do it if the boat was not set up that way by the manufacturer. You could be introdducing some back pressure issues that could be problematical. We have above the waterline exhausts but with a pair of FL120s soot is not an issue, nor is noise.
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Old 07-10-2012, 10:18 AM   #5
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Yea Marin i have thought about that and when i ask my buddy at the boat yard he said if works don't mess with it ! so i am going to toss that one out the window as i don't think my little 4-135 perkins would take much as far as back preasure and the noise is min, along with it exiting under the swim platform i have turned to good insulation and isolators in the engine room to cut down on running noise.it is now 150% better than when i bought the boat it was a dry stack that came up right through the middle of the wheel house. Boat was for fishing and few creature comforts !
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Old 07-10-2012, 01:57 PM   #6
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Water resonance reversion would be a big concern in my mind.It could kill and engine very quick.Possibly soon after start up.I've attached a pdf that goes into detail about the issue and what has been done to correct it.Opps.The pdf won't load to the forum.Here's a link to it in my google docs.

https://docs.google.com/open?id=0B0N...EJVanpOTVozQkE
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Old 07-10-2012, 03:32 PM   #7
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Water resonance reversion would be a big concern in my mind.


One small boat surveyor invented this "phenomenon" and freaked out thousands of gas boat owners without a single shred of evidenced or data that such a phenomenon even exists.

So far, about 5 years after his "discovery" neither he, nor anyone else, has films or other evidence showing water "crawling up" the exhaust pipe.

This is right up there with drug company marketing of cures for diseases that didn't even exist until drug advertising.
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Old 07-10-2012, 03:46 PM   #8
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This is right up there with drug company marketing of cures for diseases that didn't even exist until drug advertising.
Yeah, particularly the drugs to cure invented diseases that as side effects list potential problems--- like death--- that make the disease the drug is supposed to fix seem downright pleasant in comparison.
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Old 07-10-2012, 03:46 PM   #9
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One small boat surveyor invented this "phenomenon" and freaked out thousands of gas boat owners without a single shred of evidenced or data that such a phenomenon even exists.

So far, about 5 years after his "discovery" neither he, nor anyone else, has films or other evidence showing water "crawling up" the exhaust pipe.

This is right up there with drug company marketing of cures for diseases that didn't even exist until drug advertising.
I was waiting for you response......it was exactly what I was thinking...I NEVER heard of this scare...and while I'm not into yacht repair like you...I am up to my eyebrows into boating and issues affecting boating.

Your response sounds exactly what I was thinking and what so many boating mag "writers" seem to dump into the mainstream every month...utter crap based on their concern about making themselves or the mag money....facts be damned.
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Old 07-10-2012, 06:51 PM   #10
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running an exhaust outlet a couple of inches below below the waterline would not be any different than a water lift exhaust as far as back pressure is concerned. There are numerous companies making rubber elbows to clamp onto the exhaust thru hull that route the exhaust under water. Some even make SS versions with an oval shape and a slanted cut that ensures a venturi type effect when at speed on planing boats. Making sure your riser was high enough to prevent drowning the engine when docked and the stern is upstream would be about the only concern. I looked into this extensively recently as I really appreciate a quiet boat and wanted to tone down my Perkins. I think I'd really like a water-lift muffler but I'm having a time trying to figure out where it would fit. I can't find any info on how the horizontal ski boat type wet mufflers do, but they would work a lot better from a packaging point in my boat.
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Old 07-10-2012, 07:14 PM   #11
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Yeah, particularly the drugs to cure invented diseases that as side effects list potential problems--- like death--- that make the disease the drug is supposed to fix seem downright pleasant in comparison.
Right. Two years ago, "restless leg syndrome" was supposed to be a big problem, according to whatever drug company had the "cure". I guess it worked, and ended the plague, cause I never hear about it any more.
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Old 07-10-2012, 07:56 PM   #12
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I think I'd really like a water-lift muffler but I'm having a time trying to figure out where it would fit.
Here is the custom-made setup we had installed on our GB when the exhaust systems that were on the boat when we bought it began to fail. The custom-built lift muffler is fiberglass and should be good (the mfg said) for the life of the boat.

This is the port engine. The starboard engine is the same only the hose run from the elbow to the muffler is a bit longer. Don't know if this setup would have any relevance to your boat but It might give you an idea or two. The same thing could work on a single engine boat. I believe Carey has something somewhat similar on his single engine lobsterboat. As I recall his muffler, which I believe was made by the same Bellingham-based fabricator who made ours, is much larger as his boat has a 420hp turbo Cat. It is located directly behind the engine.

One nice feature of these custom-made fiberglass lift mufflers is that they have a drain at the bottom so if one has to crank the engine a lot for some reason the muffler can be drained before any water starts backing up toward the manifold and cylinders.

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Old 07-10-2012, 08:15 PM   #13
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Right. Two years ago, "restless leg syndrome" was supposed to be a big problem, according to whatever drug company had the "cure". I guess it worked, and ended the plague, cause I never hear about it any more.
ummm, you might want to find another example. RLS is most definitely a problem for those who have it and those who must sleep with them. It runs in my wife's family. Without a small dose of anti-Parkinsons medication the spasms occur every 20-25 seconds. They're fairly violent and sleep is impossible. i wouldn't wish it on my worst enemy. Not commenting on the drug-maker you're citing, because they all work hard to create a market--facts be damned--but the disease, itself, is a b**ch.
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Old 07-10-2012, 09:20 PM   #14
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sorry angus. just reacting to recent publicity on the drug companies. But the advertisements did go away.
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Old 07-10-2012, 10:01 PM   #15
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sorry angus. just reacting to recent publicity on the drug companies. But the advertisements did go away.
Hey, no worries! I hate most ads myself.

Thnx
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Old 07-10-2012, 11:56 PM   #16
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Old 07-11-2012, 12:27 AM   #17
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ummm, you might want to find another example. RLS is most definitely a problem for those who have it and those who must sleep with them. It runs in my wife's family. Without a small dose of anti-Parkinsons medication the spasms occur every 20-25 seconds. They're fairly violent and sleep is impossible. i wouldn't wish it on my worst enemy. Not commenting on the drug-maker you're citing, because they all work hard to create a market--facts be damned--but the disease, itself, is a b**ch.
+1 on different meds with dubious results.
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Old 07-11-2012, 09:40 AM   #18
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Thanks guys i am leaving well enough alone my riser elbow is about 24 inches above the exit of the exhaust and it is a steady down hill run from the engine to the stern exit. I don't like the water lift idea even though i have had them before i like the wet mufflers that are fiberglass and i have a nice spot to mount one in the engine room where the system changes from SS to fiberglass. Today i am finishing the engine room ventalition system and repainting the bilge area then working on the insulation/isolation/soundproofing and fiberglass sheeting overhead.
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