Wet vs dry exhaust

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cardude01

cardude01

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Joined
Nov 26, 2012
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5,290
Location
USA
Vessel Name
Bijou
Vessel Make
2008 Island Packet PY/SP
I have told myself myself over and over that the next boat I buy will have dry exhaust and a keel cooler. It just seems the simplest setup by far, and after working on my little Yanmar I have learned to hate heat exchangers.

However, this seriously limits the possible boats for me to look at. Am I being silly with this requirement?

Are there downsides of a dry exhaust/keel cooling system that I'm missing? There must be since not many boats use this method.
 
Personally, I like dry exhaust/keel cooling. But it is not the best setup for most boats. Read "boat mechanical systems handbook" by Gerr. Then you will be more informed on whether or not its what you really want. Everyone thinks its simpler, but that is not usually the case.
 
There are lots of dry exhaust boats here in Maine. They are pretty much exclusively working boats. The negatives of dry exhaust as I see them are:

1) Noise. Yes it is possible to install mufflers, but they are bulky. Most of the dry exhaust boats I know of are MUCH louder than wet exhaust boats.

2) Soot on deck. No way around this.

3) Heat. Dry exhausts are hot. You need lots of insulation (which does help with the noise) and the exhausts have to pass through the living spaces which takes space. Unless you are talking about a pretty big boat, this can be an issue.

4) Mufflers and dry stacks do burn out potentially leading to exhaust leaks in the living spaces of the boats.

5) There is always the risk of damaging the keel cooler if you hit something. Plus you have an extra hull penetration that is hot which makes it harder to seal and keep sealed.

6) Repairs will be pretty expensive potentially requiring significant surgery in the boat's interior.

Frankly a wet exhaust system is not at all complex.
 
cardude01 said:
I have told myself myself over and over that the next boat I buy will have dry exhaust and a keel cooler. It just seems the simplest setup by far, and after working on my little Yanmar I have learned to hate heat exchangers.

However, this seriously limits the possible boats for me to look at. Am I being silly with this requirement?

Are there downsides of a dry exhaust/keel cooling system that I'm missing? There must be since not many boats use this method.
Click to expand...

Dry exhausts while having many advantages have some rather significant disadvantages, they take up a lot of room in order to have clearances needed to prevent fires. This space is generally taken from right in the middle of the boat from the engine room all the way vertical to way above the top deck. Due to the large mufflers needed to keep the noise to a reasonable level this is a rather large waste of space for many designers. They are dirty leaving deposits and soot flakes all over the deck of your boat and others in the marina. You find them in more often in large commercial boats where these disadvantages are not as great a problem.

Keel cooling on the other hand is a great option and has no real disadvantages that I can think of with the possible exception of damage from a grounding, however with proper design and location that can be minimized to a near non-issue.

I think a hybrid system using raw water to cool the exhaust system not including the headers. With keel cooling for the engines and manifolds would be the cats azz.
 
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SCOTTEDAVIS said:
I think a hybrid system using raw water to cool the exhaust system not including the headers. With keel cooling for the engines and manifolds would be the cats azz.
Click to expand...


Yeah that would be a good setup. Don't know if I've seen that on a boat.
 
With the perspective of a lifetime of working on dry stack boats along with much more limited ownership of wet exhaust recreational boat I can say that the previous posters have hit the main points.

Noise is solvable but it costs $$$ and space. Most work boat owners don't care about noise so that is why they are so noisy.

Soot is not solvable with an older engine. The make soot. The newer tier 3 engines might be better.

Fire is not really a worry if the system is built right and well maintained. 46 yrs on the water, dozens of different boats, new, old and really old. Never an exhaust fire or leak. Ever.

Interior volume lost in unavoidable. For a 40' trawler single engine I'd think along the lines of the depth and width of a full sized fridge from the engine room to the upper deck, then the same amount some distance above the deck, then stacks going higher. All right over the aft end of the engine.

One thing not mentioned is exhaust gas flow. Look at the work boats and you will notice the stacks are high and on some angled to the side. This is because the air flow on a moving boat in relatively clam air is forward from transom to bow. If the stacks are not high enough the gasses flow down onto the deck the forward into the house. Been there, it's miserable.

Keel cooler damage from grounding is easy to solve. Build a pocket for the cooler next to the keel, this will protect from all but the most destructive groundings in which case you will have a lot more to worry about than keel cooler damage.

It's hard for me to see the advantage of a keel cooler + wet exhaust system. You'd have the complications of both systems.

If money were no object and I could have exactly what I want my architect / engineer would be asked to design a dry stack for me. But the reality is I like most I buy used boats. Most recreational boats are wet exhaust.

I like dry stack because in my opinion it is over all safer, less to worry about and without any data to back it up I think dry stack increases engine life. Unless your engine crawl space has the vertical clearance for a high riser you will introduce moisture to the exhaust valves.
 
TDunn said:
There are lots of dry exhaust boats here in Maine. They are pretty much exclusively working boats. The negatives of dry exhaust as I see them are:

1) Noise. Yes it is possible to install mufflers, but they are bulky. Most of the dry exhaust boats I know of are MUCH louder than wet exhaust boats.

2) Soot on deck. No way around this.

3) Heat. Dry exhausts are hot. You need lots of insulation (which does help with the noise) and the exhausts have to pass through the living spaces which takes space. Unless you are talking about a pretty big boat, this can be an issue.

4) Mufflers and dry stacks do burn out potentially leading to exhaust leaks in the living spaces of the boats.

5) There is always the risk of damaging the keel cooler if you hit something. Plus you have an extra hull penetration that is hot which makes it harder to seal and keep sealed.

6) Repairs will be pretty expensive potentially requiring significant surgery in the boat's interior.

Frankly a wet exhaust system is not at all complex.
Click to expand...

This pretty well nails it, but I'd add one or two minor points.

Keel coolers need to be kept clean or their ability to transfer heat becomes impaired. This isn't a huge issue, but does require attention along with bottom and prop cleaning.

Soot sucks. I've got a tier 3 engine and although I don't get flakes of soot on the boat, I do get blackening of the upper stack and surrounding gear. Cleaning soot off your transom is MUCH easier than washing down a stack and instruments 30' off the ground.

So now having owned both types of boat, I think it's a nearly even trade off between the two. Just pick your poison.
 
All of the above comments are correct. The only production recreational "trawler" that I know of that has a dry exhaust is the Nordhavn. So yes, it will very significantly limit your choices if you insist on a dry exhaust.


Also forget about trying to retrofit a dry exhaust on a wet exhaust boat. You need a 1'x1' vertical chase for the exhaust line. I don't want one of those in the middle of my galley, salon, etc.


David
 
Also some provision must be made to keep rain out of the stack pipe. If not, rain gets in there and rusts things out, and also when engine is cranked up it will spew sooty water out. Nasty!!

Regarding engines, one of the major benefits of DS and KC is it gets rid of any SW plumbing related to the engine. The "hybrid" system carries the SW downside into an otherwise elegant system.

Another complication is many modern engines come factory with SW aftercoolers and changing that design to FW aftercooling is difficult without creating a plumbing mess. Not many JWAC options out there. That's jacket water after cooler.

Still have a lot of love for dry stack.

Downeast boats are hard to build with a wet mixer high enough to keep water out of the engine. Engines mount low in the keel belly and builders like the deck right on top of the engine. So where to put an elevated mixer??? Hard to do. So that is one reason for the popularity of DS on DE boats, especially working boats where buying engines to replace water logged ones has a big effect on the bottom line!!
 
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My old Romsdahl was keel-cooled, dry stack. But a keel cooler on a steel hull is just a bunch of tubing cut in half.

My current vessel started life as a dry stack and then had a fire - there's still some charred wood in the overhead of the pilothouse. Since that's over the FRONT end of the engine, I dunno how it was plumbed but it must have been ugly.

But that was removed and a wet exhaust with a giant hydrolift in the engine room was installed before I purchased it. The cutout core in the transom came with the boat - it's great for showing someone how the hull is constructed!

Then a few years back I added a large Salisbury Hydrovac Exhaust Silencer, which effectively changed my above-water exhaust into a below-water exhaust. A little bit quieter, much less exhaust smoke under way, but I end up with some soot on the transom that I have to periodically scrub off.

I moor in freshwater and operate there much of the year, so I don't get much growth in the cooling system and zincs last a long time.

And I was able remove the cabinetry in the galley and create a storage locker, and in the pilothouse to create a giant-size berth. Huge win for me in livability for the 90% of the time I'm on the boat with the engine not running.
 
I agree with all the points made that A dry stack system is not a panacea. I have had this discussion on the dock with a few people over the years and basically it's not worth the change of an existing boat and often simply not possible without destroying the boat. However, after living with one for the last 30 years and with wet exhaust before that I am ok with my system.

It is a dry stack with a heat exchanger for the engine cooling. It works fine.

--Yes, water must be kept out of the stack when not in use. Not a big deal to make a cover. Mine is a piece of 6" pvc pipe which I then painted white and attached a tube for a handle. That cover is on anytime the engine is not running unless the weather is clear and dry.

--both system can eat up a bunch of space but I agree less with a wet. However read Boatdiesel for all the guys who lunch turbos because of a crappy wet system. There is no free lunch which ever system you have if it is done poorly.

--soot on deck. Yup, i used to get that untill I repitched the prop so the engine was under less load at the same revs. More air throughput and higher exhaust volume has kept things good for now ~8 years. ALso a lot of idling or short start/stop type runs will increase the odds of soot.

--exhaust runs do not always have to go through the cabin. Mine runs to the back deck and then up which is also where the mufflers are, in the vertical stack. But then I have a smaller boat at 32 ft so it was not difficult to setup when the boat was being built.

--Noise. Yes my boat is noisier than a comparable vessel with a wet system. It's not bad but it is not quiet. I will partly blame the engine location which is right under the salon.

--Cost., Not sure I agree here. Yes I had to do a $5K repair about 20 yrs ago but that was mostly because the tubing was too light in the first place. NOt the systems fault but the builder.

--Access. Mine runs through the engine compartment under the back deck and then up with the mufflers in the vertical shroud/cover so access is good. However with other vessels that would have to be a serious consideration. If the system runs through the main cabin or otherwise cuts the living area up then that would not be so attractive.

--Most recr. boats have a wet system for a reason that is valid.

So if you are thinking about a dry system be aware of all the angles. There is no free lunch. For a pleasure boat I would say the wet has the edge unless you simply want it, the dry, and the system does not cut up the boat.
 
The boat with a dry exhaust I'm most interested in would be on a Nordhavn. Maybe they are engineered well enough to overcome some of the negatives?
 
cardude01 said:
I have told myself myself over and over that the next boat I buy will have dry exhaust and a keel cooler. It just seems the simplest setup by far, and after working on my little Yanmar I have learned to hate heat exchangers.

However, this seriously limits the possible boats for me to look at. Am I being silly with this requirement?

Are there downsides of a dry exhaust/keel cooling system that I'm missing? There must be since not many boats use this method.
Click to expand...


Ummm... shopping again, already??

Anyway... maybe easiest to come to terms with your heat exchanger. What's the issue with that?

-Chris
 
cardude01 said:
The boat with a dry exhaust I'm most interested in would be on a Nordhavn. Maybe they are engineered well enough to overcome some of the negatives?
Click to expand...

Nordhavn are big proponents of the dry exhaust and presumably after all this time have gotten pretty good at it. However, I do know that they will build wet exhaust to customer preference (I think Ken Williams Sans Souci has a wet exhaust..). Personally, I would be more concerned about a poorly engineered exhaust wet or dry than a tested well designed of either.
 
Always shopping it seems. ?

No issues with the current HE-- just thought the dry exhaust and keel cooler would be the best set up, although that doesn't really seem to be the case.
 
Sounds like wet exhaust is much simpler.

 
A poorly designed wet exhaust is better than a dry exhaust everytime. A well designed dry exhaust on a boat designed for it is very hard to beat.
 
Love my dry stack , Keel cooled set up. Tractor engine on frames dropped into a boat. The DD is in a garage when not in use.

Build the exhaust , insolate it, bolt the cooler to the bottom of the boat and its a done deal.

WHATS NOT TO LIKE.

3288 bayliner be perfect compared to the cost of replacement on original.

Dudes it what it is !!!!!

Be a great INPROVEMENT on the likes of a 36 grand banks IMO. as a live aboard I could use the storage created <

( Grin )

Turbo ??? ya not such a great idea.
 
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SCOTTEDAVIS said:
Keel cooling on the other hand is a great option and has no real disadvantages that I can think of with the possible exception of damage from a grounding, however with proper design and location that can be minimized to a near non-issue.QUOTE]

The shipyard I am working with proposed the same system they use on tugboats, which is a keel cooler protected by a steel barrier. This would work for a fiberglass or wood boat as well. Since my vessel is low hp in comparison, I specified just split pipe welded to the hull.
Click to expand...
 

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Having had both styles I prefer the KCDS (keel cooled dry stack) by about 10-1.

Insulated double wall pipe (fire place store) with a SS exhaust inside works great , Only hassle is capturing heat to use in a wet locker.

A "Hospital critical" muffler makes it as quiet as most autos .

Soot , unburned fuel can be from an underloaded or overloaded engine , fix the prop.

IN SW Fl the lack of a seawater pump is great as the thin water is sandy, which eats impellers.
 
Yeah, Darrell Cottle with Jay Bettis Yacht Sales in Clear Lake has the listing. I met him back before I bought this boat and have been talking to him off and on since, and he wanted to list it.

I have mixed emotions about listing it. It's such an interesting boat-- easy to single hand, and everything is up to date. It's almost like a new boat. I know I won't find anything this new near this price range, but I have a crazy dream in my head.
 
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cardude01 said:
I have mixed emotions about listing it. It's such an interesting boat-- easy to single hand, and everything is up to date. It's almost like a new boat. I know I won't find anything this new near this price range, but I have a crazy dream in my head.
Click to expand...


Haven't you only done about one trip in it? One season? Found to be unsuitable? Or...?

-Chris
 
5' itis I guess.

The best explanation I can come up with is I'm a used car dealer and I'm constantly buying and selling something.

I did the trip back from Fort Lauderdale to Rockport, and made a side trip to Key West with the family.
 
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cardude01 said:
I have mixed emotions about listing it. It's such an interesting boat-- easy to single hand, and everything is up to date. It's almost like a new boat. I know I won't find anything this new near this price range, but I have a crazy dream in my head.
Click to expand...

I know the feeling and it is an interesting boat. I remember looking at it on YW several times before you bought it. It probably won't get you a Nordy but should make a nice down payment. Good luck on finding a good buyer.
 
cardude01 said:
5' itis I guess.
Click to expand...


Oh, THAT!

Yeah, been there. Although not quite that quickly. :)

And we decided to jump 9' instead of a mere 2, or 3, or 5 or whatever. Thought we might as well eliminate some of the middlemen, so to speak.

-Chris
 
devorenm said:
Nordhavn are big proponents of the dry exhaust and presumably after all this time have gotten pretty good at it. However, I do know that they will build wet exhaust to customer preference (I think Ken Williams Sans Souci has a wet exhaust..). Personally, I would be more concerned about a poorly engineered exhaust wet or dry than a tested well designed of either.
Click to expand...

I'm not sure what the exact portions are, but Nordhavn does build a lot of wet exhaust boats. I think all the twin engine boats are wet exhaust, and many single engine boats are too. In both cases I think they are all well engineered and well built. The trade-offs, in my opinion, still apply to both approaches, and assume both systems are well implemented.

So I really think it's 6 of one, or 1/2 dozen the other. And there is no way I'd try to convert one to the other. I'd just accept it's properties and move on.
 
After having both wet and dry, I'd pick dry all day. I just like not having to deal with heat exchangers, zincs, those big sea strainers, etc.
 
My aluminum boat has a hollow keel and the keel cooler lives in there. When I bought the boat it had a 6" stainless pipe from the 6CTA 8.3 engine all the way to the sky - no muffler. It was one noisy sucker. Tore it all apart, new pipe from the turbo to the new hospital-rated muffler (4' long and about 12" in diameter) nicely wrapped everything and she is very quiet, the engine makes more noise inside than the exhaust. You can use resonators to get it quieter but not needed here. No soot.

Also, the oil coolers use coolant from the circuit, no salt water at all.
 
Xsbank said:
My aluminum boat has a hollow keel and the keel cooler lives in there. When I bought the boat it had a 6" stainless pipe from the 6CTA 8.3 engine all the way to the sky - no muffler. It was one noisy sucker. Tore it all apart, new pipe from the turbo to the new hospital-rated muffler (4' long and about 12" in diameter) nicely wrapped everything and she is very quiet, the engine makes more noise inside than the exhaust. You can use resonators to get it quieter but not needed here. No soot.



Also, the oil coolers use coolant from the circuit, no salt water at all.
Click to expand...


We've had a similar configuration on our former boat (steel). Cooling water circuit contained 800 liter (210 us gal) of coolant.
Never had any issues, nothing to worry about (seacock open or closed? impeller to be changed? no seawater in the ER at all. )
And never felt that the exhaust was too noisy


best regards / med venlig hilsen
wadden
 
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