dry vs wet exhaust

[skyhawk]

I'm curious...especially from those of you that have had comparable boats with both.

daydreaming and gawking at some of these boats, it seems they could be ordered with either type of exhaust system. Some Nordhavn's for example...

Assuming both are properly designed for the boat, quality components, etc...which would you choose? why?

 

[DavidM]

Wet exhausts are quieter and easier to fit inside an engine room and the boat itself. The raw water used for exchanger cooling is used to cool the hot exhaust so it can be handled by an exhaust hose.

Dry exhausts send soot upwards to fall back on your boat, are noisy particularly on a fly bridge near the end and require an insulated chase for the exhaust stack usually through the galley/main salon. Dry exhausts either require a raw water pump for exchanger cooling or an external keel cooler.

All in all I think I prefer a wet exhaust. But if you want to give me a Nordhavn with one, I won't turn it down.

David

 

[Comodave]

Wet exhausts are quieter and easier to fit inside an engine room and the boat itself. The raw water used for exchanger cooling is used to cool the hot exhaust so it can be handled by an exhaust hose.

Dry exhausts send soot upwards to fall back on your boat, are noisy particularly on a fly bridge near the end and require an insulated chase for the exhaust stack usually through the galley/main salon. Dry exhausts either require a raw water pump for exchanger cooling or an external keel cooler.

All in all I think I prefer a wet exhaust. But if you want to give me a Nordhavn with one, I won't turn it down.

David

+1. The soot issue is a big one for me. We had a previous boat with a diesel fireplace and the soot was a PITA.

 

[DennisB1]

the key is to have boat designed around the dry exhaust system. With proper muffler the noise can be acceptable. With a keel cooler the raw water pump is eliminated making for a simpler system. I would vote for a dry exhaust if I had a choice and could afford the boat. I does take up a fair amount of room running the exhaust line so that is a negative on the living area.

 

[MYTraveler]

Although I gave serious consideration to a Nordhavn, and had been persuaded by most of the "features" that make a Nordhavn unique and presumably ideally suited to their mission of long range voyaging, I ultimately chose a semi-custom boat that was more suited to fishing. One of those features was dry exhaust. (And having had a wet exhaust trailer boat in which catastrophic damage was done to the engine because an exhaust manifold had corroded, their points about the reliability of dry exhaust resonated with me.) Because the boat I chose was semi-custom, I explored, but quickly abandoned the idea of dry exhaust -- routing the exhaust stack through the salon would be disruptive, and having the exhaust above the flybridge would interfere with my tower -- and a tower is very important to fishing. Maybe I am living in a state of ignorant bliss, but my decision was made easier because I was persuaded that risks of a well-designed wet exhaust system are minimal. In choosing between wet and dry turbos for my engines, I opted for dry (perhaps as some sort of self-compromise on the dry exhaust issue). In retrospect the wet turbos would have been a much better choice.

 

[OldDan1943]

My N46 was dry exhaust. WOT the temp would climb to the point where I had to throttle down every now and then. Each time I hauled I sent the keel cooler to a shop to be boiled out and pressure tested. The keel cooler would fit into slight cavity for protection. I might have been in 'over-kill' mode, send the cooler to a shop but, ...... maybe I should not have run it a WOT for long periods of time plus the water temp in FL is a bit higher than other parts of the world too.

Now, my AT34 has a wet exhaust. No complaints so far.

 

[Lou_tribal]

Speaking of soot I am wondering if any boat is using some kind of catalytic device to reduce it? I mean if you look at diesel cars soot was an issue 40 years ago when you were able to see blackened car trunk but nowadays it is really not the case anymore.

L

 

[PM]

If we are taking a vote, I vote for wet exhaust in any boat under about 100 feet.

pete

 

[markpierce]

Paid four figures to clean diesel soot off my trawler after crossing the Pacific aboard a ship.

 

[Lepke]

My commercial boats were all dry exhaust and private boats were wet.

No matter how you insulate dry exhaust, it's usually nosier. And it takes up space in the center of the cabin structure. If the dry exhaust piping isn't made out of stainless, you replace it every few years. There are always soot issues. Even with a proper combustion balance, moisture gathers in the piping after shutdown and next startup, is expelled as sooty water. I have been in commercial fishing boats that were dry exhaust and quiet, but had a foot or more expanding foam between the engine room and living areas. Plus about a foot of foam around the exhaust structure and 6' of foam on the inside hull. And other sound deadening material.

With some effort, wet exhaust can be quieted down close to zero. I ran covert patrol boats in the USN. They exhausted under water, the engine room was well insulated, and twin Detroits couldn't be heard at idle. That was sound deadening tech of 50 years ago.

 

[Delfin]

I'm curious...especially from those of you that have had comparable boats with both.

daydreaming and gawking at some of these boats, it seems they could be ordered with either type of exhaust system. Some Nordhavn's for example...

Assuming both are properly designed for the boat, quality components, etc...which would you choose? why?

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.

 

[mvweebles]

I'm fine with either, slight preference to wet . Twisted Tree is on his second Nordhavn build and went with wet which definitely snapped my neck towards wet. His logic is solid. Maintenance item in a wet exhaust is mostly the raw water impeller which is inside the boat and easily accessible. Dry exhaust has a keel cooler which is outside the boat.

Not a huge difference, but looking purely at wet cs dry stack doesn't tell the whole story. There are other components.

I suspect trawler folks bow go the alter of Beebe when it comes to dry exhaust. Back in the day it made more sense. Now I'm not so sure.

Peter

 

[koliver]

Commercial boats tend to have working deck, where the exhaust is more than just a nuisance, but can be a serious health hazard, so it has to be directed elsewhere. The logical alternative is to send it skyward.
Pleasure craft don't need the engine running when working on the aft deck, so there is no problem letting the engine exhaust right below the stern.

 

[markpierce]

My engine's wet exhausts exit to port slightly above waterline, often requiring closure of port pilothouse door to minimize smell, but no problem with soot.

 

[Ski in NC]

Commercial boats can have lots of variation in load. Get the tailpipe buried under water and that makes engine safety more complicated. And most commercial boats don't have a flybridge so engine exhaust note is not that big a deal. And most are keel cooled, so no need for a sea water pump. Soot on deck, who cares!! All adds up to make sense on commercial boats.

Recreational boats, wet exhaust makes the most sense for the opposite reasons.

I do like the coolness factor of dry stack. Had two boats myself with such. Kinda like riding a Harley. Fun for five minutes.

 

[IRENE]

We have a dry exhaust. All of my other boats, and those I worked on, had wet exhaust.

Some of the wet exhaust boats had relief ports on the side of the hull (Broward). I preferred scrubbing the soot from the transom and hull sides vs. random places on the upper decks, now.

I think the heat in the ER would me much less with a wet exhaust.

As Twisted Tree explained very well in another thread, with a wet exhaust, you do all of the maintenance INSIDE the boat. No diving or haul out required.

My preference would be wet exhaust if I were ordering new. Otherwise, we got what we got with the boat we wanted...dry.

 

[twistedtree]

As others have noted, I built a Nordhavn 60 with dry exhaust. Then I built a Nordhavn 68 and switched to wet exhaust, and it was frankly in the top 5 list of reasons we switched boats.


That said, there are plenty of pros and cons for each. I still have friends with dry exhaust, I still speak to them, and they still speak to me. So if you have a personal preference, go for whatever that is.

 

[skyhawk]

one of the youtube channels I watch is MV Freedom. I recall a video fairly recently where Sean was talking about a rain cap he puts over their dry stack while not running to eliminate (or more likely minimize) soot.
Does that sort of thing offset that issue enough?

 

[OldDan1943]

one of the youtube channels I watch is MV Freedom. I recall a video fairly recently where Sean was talking about a rain cap he puts over their dry stack while not running to eliminate (or more likely minimize) soot.
Does that sort of thing offset that issue enough?

Some use a flapper, others a soup can.
On the Nordhavns, I have seen pics of a rather large external muffler and a pic of where the owner had run the exhaust all the way up the aft mast.

Does anything work? I dont know.

The AT engine exhaust is on the stbd side below the water line plus a small exhaust all the way aft stbd side.

I remember we were all taught, we have about 30 seconds to check for a good flow of water out the exhaust. These days, that bit of advice holds little meaning, if the exhaust is below the water line.

 

[Ski in NC]

Flappers can keep rain out of the plumbing, but they have the annoying tendency to rattle under way.

 

[OldDan1943]

Flappers can keep rain out of the plumbing, but they have the annoying tendency to rattle under way.

LOL that could be true. I saw one flapper valve that had a weight to encourage it to stay open while underway.

Next time you are charging down the highway, check out the 'over the road' trucks and make note of their 'cure'.

I had a white 190 Benz diesel car, way way back in time. Paid $4,500 for it, brand new. I don't recall ever having a sooting problem. My N46 never had a sooting problem that could not be removed with a fresh or saltwater wash down of the upper deck.

In my feeble mind, I have lived with both and have no problem with either of them. Remember, you dance with the one who brung you.

 

[MYTraveler]

Pleasure craft don't need the engine running when working on the aft deck, so there is no problem letting the engine exhaust right below the stern.

Unless they are running a spread trolling for hours on end trying to find fish.

 

[skyhawk]

well that brings up a point....if someone wanted to hang out on the back deck while underway, dry stack going up might be better....

 

[Hippocampus]

With a following wind wet exhaust smell can be a problem. Stains from wet exhaust can be difficult to remove. So bad as to require on/off and rewaxing. A failed anti siphon can ruin a engine. Put a wire around the keel cooler tubes. Can get most of the junk off while in the water on a dive.

 

[trawlercap]

https://youtu.be/HkCvb7QLsAQ

Dry exhaust, raw water cooled twin Luggers. This is the day I bought the boat, the owner has mesh caps for start up, otherwise, I love the sound.

 

[Hippocampus]

Any read on hybrid systems? Dry stack and keel cooler with wash and wet exhaust?

Your boat is beautiful. Nothing seems to be out of that stack in that vid.

Any read on internal keel coolers? Compartment filled with fluid (coolant or petrochemical) with keel cooler immersed in that and no tubes outside? See that in Al boats. Sometimes in rolling chocks.

 

[twistedtree]

one of the youtube channels I watch is MV Freedom. I recall a video fairly recently where Sean was talking about a rain cap he puts over their dry stack while not running to eliminate (or more likely minimize) soot.
Does that sort of thing offset that issue enough?

There are really two different sooting issues, one of which can be mitigated, and the other not.


Probably the nastier sooting issue is when you start an engine and flakes of soot get ejected out of the exhaust. These land on your boat and your neighbor's and are a heck of a mess to clean up. There are two things you can do to significantly reduce this, if not eliminate it.


The first is a rain cap of some sort. When the boat is idle, if rain water drips down the stack, you will get a lot more flakes on start up. A rain cap can be an integrated flapper, or a fancier door-like device. But many people just use an old fender with one end cut off. With a rope loop on the fender and a boat hook, it's pretty easy to place/remove the fender stack cover.


The second mitigation step, typically done in conjunction with a rain cap, is to run the engine hard for 10 minutes or so right near the end of your time underway. This blows out and burns off accumulated soot, leaving less behind to blast out on start up. The combination of these two steps seems to eliminate most start-up soot flakes.


But the other sooting issue is universal, and there is no solution other than periodic cleaning. And that's the haze that accumulates over time in the area around your exhaust. With a dry stack boat it accumulates around the stack, and on a wet exhaust boat is accumulates on the side or transom of the boat. This all varies based on your boats actual configuration. This type of accumulation you will get with any and all diesels.


On my dry stack boat I never had the start-up soot flakes, but I definitely had the haze accumulation on the stack and all the instruments up in that general area. One of the reasons I favor wet exhaust is that it's much easier to clean the side of the boat or the transom than it is to climb the stack and clean all the instruments and stuff up there. Plus, everything you wash off the stack and instruments washes down over the rest of the boat below, so it's always a full boat wash, not just a localized clean up.

 

[garbler]

Not sure if this element has been touched on but transom mounted exhaust ports are the primary reason for hydro-locked engines. Sport fishing boats and many smaller near coastal commercial fish boats runs the biggest risk but gr awler type hulls with lower engines are a risk also. Fishing or whatever with stern to seas at idle or shut down allowing wave surge up the exhaust run into engines. Good mufflers have surge protectors but after years they frequently break off internally allowing seawater to pass or push through. Flappers are shunned by many and eventually fail. Lots of elevation and piping exhaust design variables but hydro-locked engines cross the claims desks all the time. It’s funny how so many reputed good builders never factor or design for this risk.

Should mention on most vessels wet exhaust runs and mufflers are terrible to access, inspect and replace. Most Taiwan builds bury the hoses in the interior joinerwork making long lengths of good hose a nightmare. Leaking internal wet exhaust runs and ports can be sinking risk also specially hose clamp connections to thru hull exhaust port fittings in a lazarette where people drop in and fill with all kinds of stuff

If your vessel is in fact designed for dry stack then lots of solutions to soot, noise etc. A dry stacked keel cooled set up is the best of both worlds in the right vessel.

 

[klee wyck]

Perhaps like most things in boats, the experience, and therefor your preference, may depend upon the individual vessel and your own bias. A well conceived system is just that, and not all boats get it right in either case.
I own both and based on my individual experience and bias, I have a very strong preference for keel cooled, dry stack.
LIBRA is free of raw water and she is clean and quiet. The chase that holds the exhaust is two feet behind the helm seat where I read 58 dB on a sound meter and on deck at 1000 rpm she is so quiet that you almost need need to look up at the stack flap to confirm she is running. I see less soot on this boat moored in Blaine than I see on a wet boat in Seattle which may just be fallout from the city.

 

[mvweebles]

I've run a number of each wer and dry. A well designed and installed system is the important element. Each have their pluses and minuses. While a dry stack may not have raw water on the inside, many/most recreational dry stack installs require large Delta blowers to cool the stack and engine room. You're almost as screwed if one of those fail as you are with a raw water pump.

There's no free lunch here. If I were building from scratch, I'd lean wet. But it wouldn't bother me to go dry if there was a compelling reason to (such as a wet install is difficult to do properly)