Dry exhaust

[BrianG]

A dry exhaust is frequently just a truck muffler welded in place.

Folks preferring a quieter exhaust should look up "hospital critical" mufflers .

There not light , not cheap, but do a great job of quieting , especially since few cruisers are at full throttle for very long.


https://www.industrialexhaust.com/silencers.php is one of dozens of choices.

Mine must of been from a Henry Ford era truck. It was loud. Loved the look of a big exhaust pipe coming up out of the deck. Looked like...a man boat.

 

[Mako]

IMO if you're building a metal hull then dry exhaust is a no-brainer. Split pipe welded against the hull, or even full pipe held proud from the hull, is easy enough to clean during monthly scrubs.

However, dry exhaust with a fiberglass hull means either full pipe held proud, requiring brackets and dozens of holes in your hull for bolts to penetrate, or a gridcooler, which has its own constant challenges to clean inbetween the fins as was mentioned earlier.

Conversion makes little sense unless someone is going through an absolutely major refit or is converting a fishing boat to a cruising (for example).

 

[FF]

Running the engines exhaust pipe thru one of the many multiple wall SS pipes made for wood stoves or fireplaces solves the hot exhaust problem.

Only downside is building in a heated hanging locker using the heat from the exhaust system is almost impossible.

Folks that live aboard and wish to use their vessel when the bay is ice free will enjoy the ease of winter operation , with no winterizing.

 

[Hippocampus]

Is the keel cooler sufficient to avoid the need for bubblers?

 

[sunchaser]

Some years ago a Nordhavn owner sold his N62 with a JD diesel and ordered a new Nordhavn with a Detroit Series 60. Both vessels were dry stack. When delivering the new N from Dana Point to BC the soot was very bad causing exterior soft cover and gel coat damage.

The new vessel could not be berthed next to other yachts due to sooting issues and liability. Very soon after delivery to the new location the Series 60 was removed from the new vessel ($$$) and a JD similar to his old N62 installed. Problem solved.

Two years ago the owner of a newly acquired dry stack paid for major cleanup on 5 vessels including ours. The marina told him to relocate his boat. I've a friend who placed a nylon stocking over his N57 dry stack to catch the soot before entering the Anacortes marina. He sold the boat.

For many dry stack is not always neighborly. Shop carefully as not all dry stacks are created equally.

 

[OldDan1943]

My 1989 46Nordhavn with dry stack, Lugger engine never caused a problem.
As much as possible we ran WOT outside from Long Island to Ft Lauderdale.

 

[Hippocampus]

Been a learning curve looking at small Nordhavns to buy. See some with twin turbo yanmars which are wet exhaust but most with naturally aspirated luggers to a dry stack . The small commercial fish boats around here commonly have truck or agricultural pump diesels repurposed for marine use with dry stacks. Now new trucks are nearly all common rail. Wonder if it makes any difference (NA, turbo, common rail) as too amount of soot at start up. Would think it would be a non issue with common rail.

 

[rslifkin]

More modern diesels will soot less. But there will often still be some soot in the exhaust system over time. If the dry stack allows that soot to get wet in the rain, or accumulate in a spot where it can get blown out at the next startup, then you may get soot splattered around at startup. I'd say it depends as much on the exhaust system design as it does on the engine itself.

 

[Fletcher500]

A lot of factors are involved, but I think it’s an accurate statement to say common rail smoke Quite a bit less than mech injection (Especially If the engine is older). I say that after using both types of engines. I spoke to Tony Athens on the phone about this subject about 4 years ago and that was his opinion as well, which counts a heck of a lot more than mine. With that said, after reading this thread I would go with a wet exhaust over a dry on a new build if both options were available.

 

[Delfin]

Some years ago a Nordhavn owner sold his N62 with a JD diesel and ordered a new Nordhavn with a Detroit Series 60. Both vessels were dry stack. When delivering the new N from Dana Point to BC the soot was very bad causing exterior soft cover and gel coat damage.

The new vessel could not be berthed next to other yachts due to sooting issues and liability. Very soon after delivery to the new location the Series 60 was removed from the new vessel ($$$) and a JD similar to his old N62 installed. Problem solved.

Two years ago the owner of a newly acquired dry stack paid for major cleanup on 5 vessels including ours. The marina told him to relocate his boat. I've a friend who placed a nylon stocking over his N57 dry stack to catch the soot before entering the Anacortes marina. He sold the boat.

For many dry stack is not always neighborly. Shop carefully as not all dry stacks are created equally.

True dat Tom. Some engines seem better suited for dry stack than others. My CAT 3306 runs quite clean, but if the boat was powered by a 3208 I might feel differently, and if a DD my neighbors might cringe at my approach. I've had to clean soot off the top deck about 10 times in 15 years, and then because I didn't run the boat up to 80% of max RPM for a few minutes to blow out any accumulation of soot before turning into anchorage or a marina. The boat is quiet underway because it is well muffled, and the stack house is well insulated. The system seems pretty much bullet proof, at least so far. As TT said, excess heat from a dry stack seems a matter of not insulating the exhaust in the ER; mine isn't hot enough not to be able to touch.


The genset is hybrid - keel cooled and wet exhaust, and I've cleaned more soot off the side of the vessel where the exhaust loop exits than the top deck.


Converting a wet exhaust system to dry seems a bit pointless as both systems, if designed from scratch, work just fine.

 

[rgano]

The custom 55-foot vessel I delivered over a 1600-mile run last spring had a JD main and two 20 KW gennies, all dry stacked right up behind the pilothouse. The boat deck aft of the pilothouse was filthy with oily soot, and the uncovered dinghy was too dirty to even consider using during our thirty days aboard. The engine had just been gone over by a JD tech including new injectors. At cruise speed I could always see a grey haze from the JD against white clouds.

 

[sunchaser]

True dat Tom. Some engines seem better suited for dry stack than others. My CAT 3306 runs quite clean, but if the boat was powered by a 3208 I might feel differently, and if a DD my neighbors might cringe at my approach. I've had to clean soot off the top deck about 10 times in 15 years, and then because I didn't run the boat up to 80% of max RPM for a few minutes to blow out any accumulation of soot before turning into anchorage or a marina. The boat is quiet underway because it is well muffled, and the stack house is well insulated. The system seems pretty much bullet proof, at least so far. As TT said, excess heat from a dry stack seems a matter of not insulating the exhaust in the ER; mine isn't hot enough not to be able to touch.


The genset is hybrid - keel cooled and wet exhaust, and I've cleaned more soot off the side of the vessel where the exhaust loop exits than the top deck.


Converting a wet exhaust system to dry seems a bit pointless as both systems, if designed from scratch, work just fine.

Delfin
The 3306 is such a great engine. As I recall you've taken much effort to insure the vessel is propped correctly. Cruising props, meaning intentionally overloaded, are for some reason a popular thing for our slow trawlers. An overloaded engine would seem a poor choice for a dry stack. Your thoughts?

 

[firehoser75]

I'd like to do something like that. How do you have things plumbed up to do the fresh water flush? I think there are lots of ways it could be done, and I'm always interested in examples and how well they work.

I freshwater flush both my engine and generator using the Groco strainer lid. I have a garden hose (with shut offf) attachment permanently affixed to the lid. Connect a dock hose to the strainer and flush with the engine running at idle for about 4-5 minutes. Just don't have the pressurized water running with the engine off without the thru hull open. The sea water intake can be either open, partially open, or closed when flushing.

 

[Fish53]

I've worked on and operated commercial trawlers for over forty years and they all had dry exhaust and there has never been a problem. That being said most pleasure boaters don't want exhaust soot on them and there is a noise issue. The complexity of having wet exhaust, the seawater pump and associated plumbing may be an issue to some as is the difficulty of operating in freezing temps. These are reasons I have dry on my personal boat just like the one I currently work on.

 

[OldDan1943]

I freshwater flush both my engine and generator using the Groco strainer lid. I have a garden hose (with shut offf) attachment permanently affixed to the lid. Connect a dock hose to the strainer and flush with the engine running at idle for about 4-5 minutes. Just don't have the pressurized water running with the engine off without the thru hull open. The sea water intake can be either open, partially open, or closed when flushing.

You have been peeking at my strainer back flushing caps and you have the same problem I do. BRASS pipe and hose connection instead of bronze. I also use a plastic hose snap gadget. Also a garden hose back-flow preventer. I use the ER FW connection along with the hose I keep coilied on board.
Also, mine is right side up too.

For safety sake, I take mine off when not in use and put the blank cap on.

 

[twistedtree]

Been a learning curve looking at small Nordhavns to buy. See some with twin turbo yanmars which are wet exhaust but most with naturally aspirated luggers to a dry stack . The small commercial fish boats around here commonly have truck or agricultural pump diesels repurposed for marine use with dry stacks. Now new trucks are nearly all common rail. Wonder if it makes any difference (NA, turbo, common rail) as too amount of soot at start up. Would think it would be a non issue with common rail.

As best I can tell, with a modern diesel (say 2009 or later), you will less or no flaky soot landing on your boat and your neighbors. We had none of that with out 2012 built Deere engine. But we still had what I'll call haze that built up on surfaces exposed to the exhaust plume. It only impacted out boat, but the stack and all the instruments up there would slowly change from white, to gray, to black. Then I'd clean them, and repeat the process.


I have heard of engines where if you change the thermostat to run the engine a bit hotter, like going from a 170F to a 180F thermostat, it clears up the soot flakes. I think that may have even been a Detroit series 60.

 

[twistedtree]

More modern diesels will soot less. But there will often still be some soot in the exhaust system over time. If the dry stack allows that soot to get wet in the rain, or accumulate in a spot where it can get blown out at the next startup, then you may get soot splattered around at startup. I'd say it depends as much on the exhaust system design as it does on the engine itself.

Good point about rain. Standard operating procedure for a Nordhavn dry stack is to cover it when not in use. A small fender with one end cut off fits perfectly over the exhaust pipe. I had a loop of rope tied to it, and could easily place it and remove it with a boat hook. And a lot of people put a stocking over the stack on startup to catch any soot blast, but I never had to do that.

 

[firehoser75]

Dan,
Yes, I don't know why the photo "inverted itself", it is fine on my computer. I have had that happen periodically on the forum before. Strange how sometimes but far from always???


I am not a big fan of dry stack. For one example, I had just finished 2 days on my hands and knees cut polishing (washed the boat the afternoon before), then separate polishing, followed by 2 coats of hand applied paste wax on the roof of my pilothouse. The very next day, I was down to the boat, and the roof was covered with black sooty, oily patches that would not wash off! There is a fuel dock about 60 yards across from me, and the marina has many commercial tugs and fish boats, all with dry stacks not that far away. It was a bit upsetting, but I could not pin point anyone in particular, just know it was from a dry stack.
I know, move the boat, but there are only so many places that a person can find moorage.

 

[FF]

"Is the keel cooler sufficient to avoid the need for bubblers?"

A bubble system is to keep the marinas pilings from being lifted by the ice with tide changes.

Old wooden boats had ice problems from the cotton in seams freezing and being started by the ice. The ice would melt and the boat could sink , no problem with a modern GRP vessel.

Being frozen in is fine as long as the seacocks are below the thickness of the ice , or secured and winterized ..

In the spring when the ice is melting it is necessary to use a pole to enlarge the ice free hole the boat is floating in to save the water line paint from being scratched.


A bubble system is much un-fun to live with , it sounds like being in a fish tank for a few months.

 

[Hippocampus]

FF in our area bubblers are commonly placed under boats if wet stored over winter. They are the concern not pilings. Being iced in can injure boats. Typical set up is shrink wrap on top and bubblers underneath. Both done even if folks aren’t living aboard. With our tides an ice free ring around boats decreases risk of damage.

 

[stubones99]

What about soot on neighboring boats?

Downside of dry exhaust is the noise and if vented up, the sooty mess which develops over time on topside surfaces.

If you spend any time warming up at the dock with dry stack exhaust, you may not get along with your dock neghbors since it soots up their top decks too. Anyone downwind is at risk of getting soot on their decks while you prepare to go out.

Most commercial boats don't have pretty white non-skid decks and a little soot isn't a big deal, but pleasure boats with non-skid decks are hard to clean the soot out of the non-skid.

 

[Hippocampus]

Interesting I’m getting conflicting information from sources outside this site.
Using keel cooler to prevent ice in makes little sense. On most boats it’s on one side only. So with one side deiced it would either force you into or away from the dock. Either your fenders would pop or your dock lines stretch and break or it would be difficult to get on and off the boat if you were in a slip. If iced in while out it might make some sense but it would be bad for the engine running with no load and would be very expensive. Basically not an option.
If you keep your stack clean and dry soot isn’t much of an issue. Straight vertical runs, high stack, covered when not running, moisture taps drained before start ups, mesh at start up and other measures decrease soot significantly. Owners tell me they haven’t had issues with neighbors if they give it a modicum of attention.

 

[mvweebles]

Hippo - I probably had 30k miles on nordhavns back in the day. I do not recall a sooting issue as described here either. I do recall a couple times with a following wind where there was some mild sooting accumulation, but not often. In all fairness, I made long runs, often over 700 mile straight shots so I didn't start-up often. And did take the precautions you cite.

Given you're looking at a N40 with a smaller 4 cylinder, I don't think you'd see much. Definitely see a little but not a big issue unless engine was not running properly.

Peter

 

[C lectric]

On my dry stack in rain country I cover the exit with a piece of painted PVC pipe with a handle attached so it is easily reached.

Biggest sooting cause was forgetting the cover and/or running too easily just before docking. Easily correctable.

Yes, I have had sooting before but never anyone else, only us.

THe last big change was when I replaced all the injectors. The engine runs cleaner now, noticeably so.

So clearly it may depend upon exhaust design, the engine, its tune and on the operator.

 

[Xsbank]

I have bought new injectors too, looks like its a lot more complicated on a Cummins than a Lehman! I also have a plastic drain pipe with a handle for the stack.

I have no salt water in my boat except for the genset. If I get soot on startup, I have a battery-powered leaf blower that takes care of it. No saltwater, no coolers with salt water, no saltwater pumps. Oops. I do have a salt-water fire pump. And it has one of those cheap-ass Jabsco rubber impellers that I hate...

My keel cooler is inside the keel so no worries there. There are better ways.

Besides, nobody would reject a boat simply because of its exhaust, you live with it.

 

[twistedtree]

Interesting I’m getting conflicting information from sources outside this site.
Using keel cooler to prevent ice in makes little sense. On most boats it’s on one side only. So with one side deiced it would either force you into or away from the dock. Either your fenders would pop or your dock lines stretch and break or it would be difficult to get on and off the boat if you were in a slip. If iced in while out it might make some sense but it would be bad for the engine running with no load and would be very expensive. Basically not an option.
If you keep your stack clean and dry soot isn’t much of an issue. Straight vertical runs, high stack, covered when not running, moisture taps drained before start ups, mesh at start up and other measures decrease soot significantly. Owners tell me they haven’t had issues with neighbors if they give it a modicum of attention.

I don't think a keel cooler would be of any use for ice mitigation, simply because it only gets warm when the engine is running, and the engine won't be running while at dock.


And for a dry stack, there are mitigation measures to control soot. The two most effective appear to be keep it covered when not in use, and run up the engine to WOT for a spell at the end of a cruise.


Honestly, I think the best type of exhaust is the one you have in your boat. Like so many things, there are pros and cons and it's really a toss up in the end. You will learn to appreciate the pros, and find ways to deal with the cons.

 

[Hippocampus]

Thanks guys. Further confirmation of what I’m hearing from other sources. What’s the longest interval before shut down that the WOT throttle period makes a difference? How long should you be at WOT for it to make a difference ? I’m assuming that’s done to blow out particulate and other products of incomplete combustion. Is that correct? Given full combustion produces water and CO2 is it to have the whole exhaust run bone dry at shut down? Why does that period of WOT help?
Also been told keel cooler fouling is much more of a problem the less frequently a boat is used and the shorter the period of time the engine is on for those runs. Am I right in assuming that’s because with frequent prolonged use growth dies and with movement falls off?

 

[klee wyck]

Thanks guys. Further confirmation of what I’m hearing from other sources. What’s the longest interval before shut down that the WOT throttle period makes a difference? How long should you be at WOT for it to make a difference ? I’m assuming that’s done to blow out particulate and other products of incomplete combustion. Is that correct? Given full combustion produces water and CO2 is it to have the whole exhaust run bone dry at shut down? Why does that period of WOT help?
Also been told keel cooler fouling is much more of a problem the less frequently a boat is used and the shorter the period of time the engine is on for those runs. Am I right in assuming that’s because with frequent prolonged use growth dies and with movement falls off?

I only have the experience of one dry stack and keel cooled boat, so pretty limited. However, no soot problem that I have ever detected. I never run WOT.
No fouling on the cooler which, on this boat, is just a box on the hull that looks like a bilge keel that is full of coolant. See photo. No fouling.
And, regarding water coming into the exhaust path, of course the stack is equipped with a flapper cap with an adjustable counterweight just like all good on land construction equipment that has a vertical stack. Not rocket science.
A bucket over the stack...really?

 

[C lectric]

I disagree with WOT. All you need do, if indeed a harder operation is needed, Is to crank it up higher than you normally operate.
Another 200 to 300 revs for several minutes should take care of it.

I will add that when you start In morning don,t idle your engine for 1/2 hr. Get moving slowly but get a load on it. All should be ready except the line needed to hold in place,
Start ,cast off and go.

Cover the stack when not operating.

 

[guy with a boat]

My main engine has a dry stack and we have never had a sooting problem. Not any noticeable soot on our boat and no complaints from neighbors. We have a recent (2015) Deere 6090 and I do run it up to 70% power for 15 minutes or so sometime in the last hour of a long run, and those factors may help.

Our wing engine (Deere 4045) is a wet exhaust, so I still get to change an impeller every year or two. Regarding noise, the wing is noticeably louder than the main, despite being half the size. I don’t know if the exhaust systems play a role in that or not.

Lastly, I have never put a bucket or any other cover over the exhaust. I’m not sure how to explain the difference between my experience and those of some others, but we have zero complaints or issues with the dry stack.

I think either system can be equally desirable, and the quality of design and construction of the boat is far more important than the type of exhaust system.