Exhaust on the side

[KiwiExplorer]

Hi all

My exhaust currently comes out under the duck board aft, the fumes tend to suck into the cabin, I am moving it to the port side about 1 m forward of the transom.

I have 2 questions?

1. should the new outlet be under, waterline center or above the water line?
2. The exhaust has a 300+ mm rise above the water line inside, will a rubber flap be enough on the side to stop swells washing up the pipe?

any and all advice would be appreciated

Thanks

 

[markpierce]

All the "wet" exhausts of water-cooled engines in my limited observations over the last 50 years have been above the waterline. Diesel "perfume" will vary/be present dependent on variables such as the wind direction. My boat has the exhaust above waterline on the portside, adjacent to the engine compartment, under the pilothouse. This minimizes the length of the exhaust line.

Love the sound of the water-laced exhaust of a low-RPM diesel engine.

 

[Hendo78]

All the "wet" exhausts of water-cooled engines in my limited observations over the last 50 years have been above the waterline. Diesel "perfume" will vary/be present dependent on variables such as the wind direction. My boat has the exhaust above waterline on the portside, adjacent to the engine compartment, under the pilothouse. This minimizes the length of the exhaust line.

Love the sound of the water-laced exhaust of a low-RPM diesel engine.

mate have you got any full length pics so i can see where the exhaust is in relation to the rest of the boat? ... i'll be cutting mine soon and have thought the same Q's the OP has asked

Cheers mate
Matt

 

[RickB]

... i'll be cutting mine soon and have thought the same Q's the OP has asked ...

Several issues to keep in mind:

If you use a simple but cheap waterlift muffler close to the overboard you will have a cycle of dry exhaust followed by a spurt of water. The noise may be very annoying to some people.

If you run a straight dry exhaust line overboard, the noise created when the boat rolls and submerges the outlet will probably be very annoying to a lot of people.

The best and quietest systems I have seen use a muffler before the spray ring followed by a water separator. The water is discharged below the waterline and the cooled exhaust gases flow smoothly and quietly to an outlet just above the water line. The length (volume)of the system allows for a low differential pressure to develop when the outlet is submerged and greatly reduces the noise spikes. A longer run also provides more protection against waves flooding the system. Make sure the piping from the water separator is constantly down so there are no low spots to collect water.

Exhaust should be neither seen nor heard.

 

[OFB]

different strokes

Rick



I love the "dry stack" exhaust system on the old boat , even if one can see it.

No its not a system to convert to in this application IMO.

Just sayin.

 

[markpierce]

mate have you got any full length pics so i can see where the exhaust is in relation to the rest of the boat? ... i'll be cutting mine soon and have thought the same Q's the OP has asked

Cheers mate
Matt

That's the best I've got. All that's missing in the photos are the two elbows at the top of the system.

 

[markpierce]

It's comforting to peek over the railing and see the water mixed with the exhaust, knowing the raw-water cooling system is working.

 

[Sailor of Fortune]

Or you can do like Robert Beebe and have a diverter valve to the galley sink.

 

[Conrad]

Several issues to keep in mind:

If you use a simple but cheap waterlift muffler close to the overboard you will have a cycle of dry exhaust followed by a spurt of water. The noise may be very annoying to some people.

If you run a straight dry exhaust line overboard, the noise created when the boat rolls and submerges the outlet will probably be very annoying to a lot of people.

The best and quietest systems I have seen use a muffler before the spray ring followed by a water separator. The water is discharged below the waterline and the cooled exhaust gases flow smoothly and quietly to an outlet just above the water line. The length (volume)of the system allows for a low differential pressure to develop when the outlet is submerged and greatly reduces the noise spikes. A longer run also provides more protection against waves flooding the system. Make sure the piping from the water separator is constantly down so there are no low spots to collect water.

Exhaust should be neither seen nor heard.

That makes all kinds of sense for a genset, but is it practical for the main engine? Just wondering about the volume of water/exhaust gases at higher speeds.

 

[RickB]

That makes all kinds of sense for a genset, but is it practical for the main engine? Just wondering about the volume of water/exhaust gases at higher speeds.

Works well on DD 2000s, 4000s and CAT 3500 series propulsion engines and a whole range of generators up to 350kW and higher. Those generators are the same size and type commonly installed as main propulsion engines on little boats.

Some higher power boats and many large yachts use a (manual or automatic) diverter valve to direct all the water and exhaust underwater at high power to keep the noise and fumes well aft of the boat. Normal slow operation is the way I described, the exhaust goes out through a muffler (optional) to a spray ring then a water separator and side or aft exhaust pipe. Some have only an aft outlet and place the spray ring near the transom.

A good marine exhaust firm can do pretty much anything you like. Most do a far better job than the production builder who builds for minimum cost and could care less about backpressure, efficiency or esthetics.

 

[Conrad]

Works well on DD 2000s, 4000s and CAT 3500 series propulsion engines and a whole range of generators up to 350kW and higher. Those generators are the same size and type commonly installed as main propulsion engines on little boats.

Some higher power boats and many large yachts use a (manual or automatic) diverter valve to direct all the water and exhaust underwater at high power to keep the noise and fumes well aft of the boat. Normal slow operation is the way I described, the exhaust goes out through a muffler (optional) to a spray ring then a water separator and side or aft exhaust pipe. Some have only an aft outlet and place the spray ring near the transom.

A good marine exhaust firm can do pretty much anything you like. Most do a far better job than the production builder who builds for minimum cost and could care less about backpressure, efficiency or esthetics.

Interesting - thanks RickB. Always fascinating to hear about technically "pure" solutions.

 

[Phil Fill]

All the Eagles thru hull are above the water line except for the raw water in take for the e.gines. The exhaust is also above the water line. The Eagle was dry exhaust but was hot and noisey. Converted to wet which cooled and quieted the exhaust. Had a modified water muffler the gravity drain made an install at a local muffler shop. Any way thru hulls and exhaust above the water line.

As for side exhaust when the wind is blowing right you will still get fomes. The cheapest and easest is change the course. I been burning the newer ultra sulfur diesel mainly for thr diesel boilet which burns very clean. I can stand in front of the boiler exhaust, and NO sutt.

 

[AusCan]

I also get exhaust fumes, being raw water cooled and therefore running a low engine temperature, the engine is probably not burning as cleanly as some.
Surprisingly it is worst is when I am heading directly into the wind.

The best solution I have found so far is opening the forward facing cabin windows and hatches to get maximum air flow out the cockpit door. This minimises any backdraft which sucks the diesel fumes into the cockpit.

 

[Searios]

As for side exhaust when the wind is blowing right you will still get fomes. The cheapest and easest is change the course.

Or have a North Sea type exhaust - which exits on both sides of the hull - so the fumes will most likely exit on the down wind side.

 

[RickB]

I guess that would work if your boat always leans into the wind.

 

[Searios]

I think that the water from the exhaust will always exit on the leaning side - and I think the the exhaust fumes generally will exit on the downwind side - I haven't used the system so I am guessing.

 

[Brooksie]

Or have a North Sea type exhaust - which exits on both sides of the hull - so the fumes will most likely exit on the down wind side.

Agree but not because of fumes. A single side exhaust can repeatedly roll water into your waterlift filling it and then your engine while anchored in a seaway. The "northsea exhaust" or a water seperator will prevent this and the former insuring that exhaust exits on the lee side.

 

[Hendo78]

That's the best I've got. All that's missing in the photos are the two elbows at the top of the system.

thanks for your reply mate but i was referring to an external shot of your boat showing the location of the exhaust outlet in relation to the rest of the boat

 

[Searios]

Agree but not because of fumes. A single side exhaust can repeatedly roll water into your waterlift filling it and then your engine while anchored in a seaway. The "northsea exhaust" or a water seperator will prevent this and the former insuring that exhaust exits on the lee side.

Agree, but this problem can be eliminated by installing a waffer type valve - basically its a simple valve that can be closed with a lever when leaving the boat.

 

[Searios]

thanks for your reply mate but i was referring to an external shot of your boat showing the location of the exhaust outlet in relation to the rest of the boat

Basically, the further away from windows, door openings or hatches the better - obviously, the further aft is usually better.

But - if you install the dual exhaust North Sea type then it doesn't really matter since the exhaust fumes will (most likely - disclaimer) exit on the downwind side.
But - if - on a downwind leg, then it might even be better to have a forward exhaust, since the gasses MIGHT blow ahead of the boat.....
Just saying that there is no perfect system...

 

[Searios]

hmm, I don't know of anyone that has posted more pictures of his boat than Mark, so I surely expect him to either link to an old post or post another pic of his super boat.

Mark -it can't be true that this is the best pic you can do....

 

[RickB]

The "northsea exhaust" or a water seperator will prevent this and the former insuring that exhaust exits on the lee side.

So, your boat always leans into the wind? The lee side is higher than the windward?

Does the water discharge uphill and the gases downhill?

Will a submerged exhaust pipe offer less resistance to gas flow than one above the water?

 

[markpierce]

thanks for your reply mate but i was referring to an external shot of your boat showing the location of the exhaust outlet in relation to the rest of the boat

Portside, below the pilothouse, under which is the engine compartment.

 

[Searios]

So, your boat always leans into the wind? The lee side is higher than the windward?

Does the water discharge uphill and the gases downhill?

Will a submerged exhaust pipe offer less resistance to gas flow than one above the water?

That's exactly the point with the North Sea type exhaust..............


I'm sure that that you are just joking, so I will follow you: yes - water will run uphill and hot exhaust gasses will naturally run downhill due to being hot

and to reply to Rick: - NO - as mentioned - hot gasses will normally exhaust downwind (depends on the force of the wind) and in a some situations the gasses will exhaust upwind or downwind (depends on the force of the wind....)

 

[KiwiExplorer]

Thank you very much for all the feed back.
I have moved my exhaust to the port side, exiting just above the water line, However having a hard chine hull, she tends to snap roll, this in the right combination of circumstances could flood my silencer then possible the engine.

Has anyone used a non return valve to ensure there is no flow back into the silencer.
I have seen them up to 100mm, made of steel, stainless and high pressure plastics of sorts.

 

[BruceK]

Definitely do something, and be sure it works. Water in an engine does not compress.
I broke the crankshaft on a small Volvo yacht (sailboat) engine. The mechanic said the engine "hydrauliced", after sailing for a long period heeled with the exhaust outlet under water, despite an exhaust trap and above water loop. Result, new engine.

 

[Peter B]

Frankly, with a wet exhaust, I would favour leaving it at the stern, and maybe looking to improve through the boat airflow. Our exhaust is like that, and the only time we get a bit of a smell in the boat is with a tail wind. If that happens we open the front window and get a bit of ram air through her if possible, or just close the rear door and windows, ad appreciate we are getting better speed and economy. Seldom happens tho. Not where we sail anyway. I really don't like the idea of an open wet exhaust outlet on the side where it could get submerged and water forced up it, valve or no valve...and fumes could well still come in, maybe moreso, as often the wind is on the beam. Just sayin'...

 

[Codger2]

Agree but not because of fumes. A single side exhaust can repeatedly roll water into your waterlift filling it and then your engine while anchored in a seaway. .

I'm a little confused as to the perceived problem. (Not the fumes...that's easily solved) If the exhaust out- let is partially in the water but the hose elbow to the water lift muffler is well above sea level, (several feet) how does the water intrude into the engine?

 

[Baker]

Find out where you water line is Walt. And then see how high your turbo is above the waterline. Because that is the path it will have to take. It is likely closer than you think. I think you want a minimum of 12 inches. My boat is one of those that Cummins signed off on the installation and it is allegedly less than 12 inches although I haven't measured. It seems more than that but Timjet says his is only 9ish inches above the waterline and I think he has had damage to his turbo due to water intrusion. Just remember how low your engine is in your boat. Now if you have a "loop" or a point where your exhaust goes higher than your turbo then that helps.

It is ultimately simple physics. If the water CAN flow....it will.