dry vs wet exhaust

[firehoser75]

Where I moored, there are a large number of commercial boats (both fishing and Tugs) all with dry exhaust. Also the harbour is a busy seaplane port. I found it annoying trying to "take care of my boat" and keep it clean. One time, after spending 2 full days on my hands and knees cut polishing, polishing, then waxing just the pilothouse roof, I came back 2 days after that to find the roof covered with black, sooty, oily marks that would not wash off!!!!

That is one reason why I don't like dry exhaust. It is not fair to your neighbours, IMHO.

 

[Ski in NC]

I had a 30-odd foot woodie with 453 Detroit and dry stack on my dock. Engine was rough for a bunch of reasons and I tied it up behind my shop/house to do some work over a month. Finally got engine in good shape and owner and I and others would go for some putt-putt cruises.

Crap got on the deck all over. Some chunks, some oily goop. Everyone complained about crapping up their shoes, carpet in cars, carpet in house. Want to ruin some clothing and carpet? Get some detroit vomit on it. Done.

I knew a good bit of it was from easy running with a sick diesel. So I took the boat out with some earmuffs and ran it HARD. Did I mention it was loud?

I watched the stack and it started to throw out smoke. Then noticed some red-hot patches on the piping and muffler. Stack fire!!! Nothing was at risk of catching fire (external muffler away from any wood), so I just kept the hammer down. Went about four miles, still throwing crap out the stack and the hotspots were moving around. I ran out of channel and spun the boat around and put the hammer back down. After about ten miles the smoke and crap and hotspots went away.

Pulled back into my creek and tied it up. Sh!t all over the deck. I told the owner about it and he came down the next day and did a good wash down.

Never again was there a problem with sh!t on the deck. I told the owner (and his Dad, who ended up owning the boat) to run it up near "on the pins" and watch the stack. You will see some smoke. Keep on it til no more smoke. Never again was there a problem with sh!t on the deck.

Gotta keep them pipes clean!!!

 

[Mako]

IMO for a new build if you’re building in metal then you go dry stack because welded split pipe or channel is a no-brainer.

However stack and exhaust exit placement is very important in my experience.

Going for the modern aesthetic of a central stack (like the Nordies) with all your instruments mounted on it will result like what Twisted has mentioned.

Best is an asymmetric stack, all the way to port or stbd beam, and run an extended exhaust pipe out at 45° so it reaches the plane of your gunwale.

Likely the only soot you’d experience at startup would be if in a slip and the exhaust is upwind.

 

[psneeld]

From a vessel engineer who invents and installs clean exhaust systems on vessels...granted most are larger and more expensive than this forums average trawler.....

"Why do all those people think that a dry exhaust requires a keel cooler or that dry exhausts can't have water jacketed exhaust manifolds and seawater heat exchangers?

We install wet and dry exhausts on boats every day and rarely ever see a keel cooler or an uncooled exhaust manifold. We use wet mufflers and drain the water overboard beneath the waterline and dry exhaust out the side or the stern. We run exhaust from the manifold either up the stack through a muffler or to the fiberglass wet muffler. And yes, there are catalytic soot removal product used on yachts, we build and install them and have close to 100 working all over the world."

 

[twistedtree]

"Why do all those people think that a dry exhaust requires a keel cooler or that dry exhausts can't have water jacketed exhaust manifolds and seawater heat exchangers?

I think dry exhaust + seawater cooled was mentioned earlier. And nobody said anything about exhaust manifold jacketing. Being argumentative like this is why RickB is scraping paint instead of here to say this directly.

 

[OldDan1943]

IF you have a keel cooler, may I suggest you make if a tad bit over size and adjust the engine temp by selecting the temp with the engine thermostat. I feel this option allows you to adjust the temp for the temp of the water you cruise in.

 

[Sabre602]

My late father-in-law had a dry stack on his old Meadows diesel, and we have a dry stack on our Lehman 120. I like them. We do have a bucket that we invert over the stack that keeps the water out, and soot is really minimal. Both boats had/have Dickinson diesel ranges that put out more soot than the main engine by far. Noise? Not an issue. On my FIL's boat the stack came up just outside the after pilothouse bulkhead, so was actually in the cockpit. On ours it's just inside the after bulkhead of the pilothouse, adjacent to the diesel range. It's a favorite spot to lean against in cold weather. Both with keel coolers; no problems there.

I really like keeping salt water outside the boat. Personal preference.

 

[sunchaser]

Soot is largely a function of the engine. Some are soot creators, some not so much. My CAT 3306 doesn't produce much soot, and in 15 years of running, I suppose I've cleaned soot a dozen times, if that. I;ve cleaned soot from the genset that is wet exhaust many, many more times over the years. The space required is a raceway that butts up against the galley counter. On one side I mounted a Newport diesel heater, which we use all winter. Because of where the raceway is located, its practical impact on usable space is essentially zero.


I do run the engine up to 80% WOT for 10 minutes before returning to the slip and that seems to blow out any accumulated soot. I also built a a stainless steel faux stack mounted over the actual exhaust stack that keeps rainwater out. Sound wise, I measure 62 db in the pilot house, and the exhaust is located immediately behind the PH in a "stackhouse" that also holds the hot water tank and Kabola boiler. So noise is hardly a problem.


Bottom line, like most stuff on boats, if properly thought through and well designed and the engine is not one that produces a ton of soot (thinking about DDs, CAT 3208s, etc.), a dry stack/keel cooler is a simple, quiet system. You mileage may vary.

Good points Carl. We walked past Delfin today and I spent an extra few steps looking for soot. She was clean as a whistle. No neighbors were protesting either from what I could see.

 

[Simi 60]

Wet exhausts are quieter and easier to fit inside an engine room and the boat itself.

You haven't seen the size of our wet exhaust.
Quiet yes but it takes up a lot of space
27 inches tall, 20 inches in diameter with 8 inch fibreglass tube running 3/4 of the length of vessel.

 

[FF]

After a bunch of boats over the years KKDS Keel cooled dry stack is my chice.

Noise is not a problem , A hospital critical muffler , can bring the sound down to a Buick level.

Soot is less of a hassle if the right size engine is fitted , its the big engines with low loads that soot.
Modern electronic engines do very little.

"IF you have a keel cooler, may I suggest you make if a tad bit over size and adjust the engine temp by selecting the temp with the engine thermostat. I feel this option allows you to adjust the temp for the temp of the water you cruise in."

While this will work its simpler to have an oversized cooling setup that can handle a big load under tropical conditions , with modest fouling.

The cure is a bypass thermostat that returns some coolant back to the engine , and sends the rest to the keel cooler. If the engine runs at 180F the return thermostat setup would return 160F water , so no thermal shock .

A proper KKDS system just requires a OK NA , and a builder to source the parts.

On steel hulled vessels the cooler can be internal with the hull plating , so no extra drag , cleaned with a scrub brush if needed.

__________________

 

[rslifkin]

You haven't seen the size of our wet exhaust.
Quiet yes but it takes up a lot of space
27 inches tall, 20 inches in diameter with 8 inch fibreglass tube running 3/4 of the length of vessel.

Yeah, the quiet ones can be pretty big. Mine are even bigger if you scale proportions to the size of the boat (plus having 2 engines). Each engine has a 26" tall, 12" diameter 2 stage water lift muffler on it. Then a 5 inch fiberglass tube on each side running about 12 feet from the aft outboard corners of the engine room to the transom. But they are very quiet.

 

[garbler]

Soot is largely a function of the engine. Some are soot creators, some not so much. My CAT 3306 doesn't produce much soot, and in 15 years of running, I suppose I've cleaned soot a dozen times, if that. I;ve cleaned soot from the genset that is wet exhaust many, many more times over the years. The space required is a raceway that butts up against the galley counter. On one side I mounted a Newport diesel heater, which we use all winter. Because of where the raceway is located, its practical impact on usable space is essentially zero.


I do run the engine up to 80% WOT for 10 minutes before returning to the slip and that seems to blow out any accumulated soot. I also built a a stainless steel faux stack mounted over the actual exhaust stack that keeps rainwater out. Sound wise, I measure 62 db in the pilot house, and the exhaust is located immediately behind the PH in a "stackhouse" that also holds the hot water tank and Kabola boiler. So noise is hardly a problem.


Bottom line, like most stuff on boats, if properly thought through and well designed and the engine is not one that produces a ton of soot (thinking about DDs, CAT 3208s, etc.), a dry stack/keel cooler is a simple, quiet system. You mileage may vary.

When I worked on Delfin back in the 70’s I recall the original owner, Don Tyler, commenting on fuel quality causing smoke and soot problems. He ran on cheap Mexican fuel a couple of seasons and sulphur content was high according to a lab test. But once he got back on better fuel that big Volvo was quite clean, maybe a short puff when he first lit it off. What a wonderful vessel you have there so much CCA cruising history and capability.

 

[DCDC]

Our boat has twin JD6068’s with dry stacks and Fernstrum keel coolers. Our experience after 3 years of cruising (6 months/2K nm per year, 6 months at dock, Gulf Coast for hurricane season):

- the exhaust system is well designed into the boat. The risers run up the cabin sides are insulated within heavy aluminum supports. Inside you would not notice them unless pointed out. Above deck the run inside aluminum housings which are integrated into instrument arches and paravane structure.

- mufflers and high discharges (25’, not a loop boat) keep noise down. The exits are angled aft, have weighted flappers and cowlings which minimize rain entry.

- the keel coolers work well and, other than a mid season barnacle scraping and 18 month zincs, are maintenance free.

- engines burn clean so soot is minimal. Some haze near discharges. Never any on deck when cruising. Some on aft deck on first start after idle for months in wet climate but manageable. Never any on dock or other boats.

 

[twistedtree]

After a bunch of boats over the years KKDS Keel cooled dry stack is my chice.

Noise is not a problem , A hospital critical muffler , can bring the sound down to a Buick level.

Soot is less of a hassle if the right size engine is fitted , its the big engines with low loads that soot.
Modern electronic engines do very little.

"IF you have a keel cooler, may I suggest you make if a tad bit over size and adjust the engine temp by selecting the temp with the engine thermostat. I feel this option allows you to adjust the temp for the temp of the water you cruise in."

While this will work its simpler to have an oversized cooling setup that can handle a big load under tropical conditions , with modest fouling.

The cure is a bypass thermostat that returns some coolant back to the engine , and sends the rest to the keel cooler. If the engine runs at 180F the return thermostat setup would return 160F water , so no thermal shock .

A proper KKDS system just requires a OK NA , and a builder to source the parts.

On steel hulled vessels the cooler can be internal with the hull plating , so no extra drag , cleaned with a scrub brush if needed.

__________________

I think this is all true, but one very important comment earlier is that you dance with your own date. Yes, a dry exhaust can be muffled to no more than the hum of a drier vent. But is your boat built that way? Mine did actually have a "Hospital Critical" grade muffler, but I still found it objectionable. I looked at adding a second muffler and came close to pulling the trigger. Amazingly, there was space to fit one which is probably what kills the idea for most boats. But when calculating the back-pressure, it became clear that the whole exhaust pipe run would have had to be upgraded to once size larger, then all new insulation, etc. It just wasn't practical with that date.


But if you have a boat with dry exhaust, dance with it. There are plenty of ways to work around the issues. And if you have wet exhaust, dance with it. There are ways to work with it.

 

[C lectric]

I was ignoring this thread because it has been covered many times.

I have had a dry stack boat for 35 yrs now. It does NOT have a keel cooler, rather a heat exchanger with a raw water discharge over the side.

I use to have periodic messes but not for many years now since I did several things:

--cover the stack whenever the boat is not being used. No Flapper and I did consider one but nixed it. Stops rain entry which definitely made things worse. The application of the cover is part of the shutdown, not an afterthought. I went through several covers. It is now a piece of PVC pipe, painted for appearance, and a handle of rail fittings and long enough for me to reach easily. This thing is heavy enough that even though I periodically forget to remove it, the thing stays put which will mean any soot that does blow out will not cover any other boats, just ours. It is not heavy , just enough to not get blown off.
--keep the engine in tune.
--got the propeller repitched some years ago. It was overpitched leading to too much fuel for the air intake volumn and producing smokey operation. Once this was done at the same revs the exhaust trail was far less obvious. Even when I want the lost boat speed back and push the throttle up the engine still produces far less smoke.
The total exhaust flow including the intake air is far greater so the fuel burns cleaner and less soot takes roost in the muffler/stack.
--periodically raise cruise rpm up several hundred rpm to blow out the stack. It works.
--if the wind is blowing the exhaust directly over the boat I change direction slightly. This has been needed VERY seldom.
--if sooting of other equipment is likely then raise the stack. May not be practical but take a look. I installed a radar dome 3 yrs ago right in front of the stack and there is NO sign of darkening.

That I recall I have NEVER smelled the exhaust which I cannot say about transom exhaust exits, seldom as even that smell was.

I also have a diesel stove which still gets lots of use. Used to get a lot more use, a Dickinson Pacific. If it sooted it was not being operated properly or it was not setup properly. If you don't want or like one that's fine but they do NOT have to be soot generators.

 

[FF]

Most Dickinson smoke problems seem to happen in marinas in high winds where other vessels will change wind direction , that can puff a low flame out.

The H style smoke head usually solves any problems.

 

[guy with a boat]

Its all about execution and details. We have a dry stack and our experience with it has been great. We have no visible sooting. The engine (2015 Deere 6090) runs pretty clean, with no visible smoke, so that helps. We run it up to 70-80% power after a long run, which may also help. Whatever the reason, we don't see any soot on the boat. I don't cover the stack at all. The last section runs close to horizontal at the exit so that helps avoid water entry from rain.


Regarding noise, our main with dry stack runs quieter than our wing engine with wet exhaust. Not sure why that is, but it is noticeable. The wing is half the size of the main.



They both work well and I would be happy with either wet or dry as long as they are executed correctly.

 

[Fletcher500]

Its all about execution and details. We have a dry stack and our experience with it has been great. We have no visible sooting. The engine (2015 Deere 6090) runs pretty clean, with no visible smoke, so that helps. We run it up to 70-80% power after a long run, which may also help. Whatever the reason, we don't see any soot on the boat. I don't cover the stack at all. The last section runs close to horizontal at the exit so that helps avoid water entry from rain.


Regarding noise, our main with dry stack runs quieter than our wing engine with wet exhaust. Not sure why that is, but it is noticeable. The wing is half the size of the main.



They both work well and I would be happy with either wet or dry as long as they are executed correctly.

What happens to the rain water that gets trapped in that horizontal run if you don't cover your stack? I would assume the engine exhaust doesn’t have the ability to clear it out when you start it up again?

 

[Capt Ray]

I married the girl who (when we first met) got a big kick out of the fact that I had a rubber bucket to throw sea water on the dry exhaust every 30 minutes or so, from a large 4 cylinder Gray Marine. The 30 foot open double ender's wooden hull was a bit too close for clearance to the place where the dry exhaust went out the port side amidships. Rather than redesigning it all, I just used a bucket! No problem. <grin>

Today, 35 years later, that girl is still with me. But today she prefers the wet exhaust that our trawler came with. LOL ... no embers...

 

[KarmaII]

I like mine

Wet, nothing hidden, plenty of room and not to hot. Nordhavn N5902 Coastal Pilot

 

[OldDan1943]

Wet, nothing hidden, plenty of room and not to hot. Nordhavn N5902 Coastal Pilot[/QUOTE


Now you are bragging.

 

[guy with a boat]

What happens to the rain water that gets trapped in that horizontal run if you don't cover your stack? I would assume the engine exhaust doesn’t have the ability to clear it out when you start it up again?

There are several drain slots across the bottom of the pipe just inboard of the exhaust end. Water that finds its way in the end mostly drips out the slots. I’m sure some water makes its way past the slots but apparently not enough to cause a problem. The boat has seen it share of rain in Florida and BC and so far, so good.

As a side note, I did have some rain water running down the outside of the pipe and making its way into the stack enclosure. I added a small ring around the pipe before it enters the enclosure and that makes the water drip off and seemed to correct that water entry.

 

[Fletcher500]

There are several drain slots across the bottom of the pipe just inboard of the exhaust end. Water that finds its way in the end mostly drips out the slots. I’m sure some water makes its way past the slots but apparently not enough to cause a problem. The boat has seen it share of rain in Florida and BC and so far, so good.

As a side note, I did have some rain water running down the outside of the pipe and making its way into the stack enclosure. I added a small ring around the pipe before it enters the enclosure and that makes the water drip off and seemed to correct that water entry.

Got it, makes sense.

 

[SP3]

We have a conversion with a dry stack. The sound in the pilot house is noticeable as the engine is underneath it and the exhaust runs up the plenum behind the pilot house with a muffler. Conversation in the pilot house while running is normal and does not require raising ones voice. Interesting thought about replacing it with a hospital muffler.

I have seen soot expelled at start up, but adding a cover over the exhaust when not running seems to prevent that and we have yet to have to run up and swab the decks.

It's a bit loud on the top, but the exhaust is just a pipe and has no covering. We do the "italian tune up" and run the RPMs up when we are returning to the marina to heat things up, although the keel cooler seems to keep the engine temp the same no matter what is going on. We have a John Deere and you have to look for the exhaust plume when cruising.

 

[tn6437]

not to change the subject but.. since we a are talking about exhaust. i was idling for about 20 minutes while waiting to lock through and noticed a diesel sheen on the water around my boat in the water. diesel fuel floating on the water. later that day when i docked the engine idled for a few minutes and i noticed it again. is it normal for the wet exhaust to have some unburnt fuel in it ?

 

[MYTraveler]

not to change the subject but.. since we a are talking about exhaust. i was idling for about 20 minutes while waiting to lock through and noticed a diesel sheen on the water around my boat in the water. diesel fuel floating on the water. later that day when i docked the engine idled for a few minutes and i noticed it again. is it normal for the wet exhaust to have some unburnt fuel in it ?

Depends on the engine. My DD892s would do that, and I suspect at least some of the sheen was due to oil. That caused me to study the exhaust of other boats, and in my observations, the problem was not limited to DD's. But, even with DDs it shouldn't happen and may be caused by a bad injector or two. Conversely, my Cummins QSM11s don't do that. In fact, it takes careful scrutiny to see any hint of exhaust smoke with these engines, and even then the only time it can be seen is right after startup. Otherwise, none, even after prolonged idling.

 

[OldDan1943]

May I suggest you have the injectors 'pop tested'?
I suspect one or two of your injectors are not closing all the way resulting in a very small drip at idle.

 

[tn6437]

sheen on water

i probably should have mentioned that my engine is a caterpillar 3116 ta . i have never heard of pop testing the injectors, but then i have only owned one boat with a diesel engine.
i appreciate the replies, thanks guys.

 

[MYTraveler]

i probably should have mentioned that my engine is a caterpillar 3116 ta .

It may help to diagnose the source of your problem if you can determine which (or whether both) engine/exhaust is creating the sheen.

 

[Gdavid]

i probably should have mentioned that my engine is a caterpillar 3116 ta . i have never heard of pop testing the injectors, but then i have only owned one boat with a diesel engine.
i appreciate the replies, thanks guys.

Pulling and re-installing the injectors on those engines is no small task. There is quite a process involved to install and adjust them. It may be worth the considerable expense of having a Cat mechanic look over the engine on the water prior to pulling the injectors.