Keel Cooling, Fouling and Dry Stack

[KiwiClive]

Hey guys,
Does anyone here have any trouble with fouling of the keel cooling matrix?
Does the hot engine water keep the barnacles at bay?
We berth in an area where barnacles and oysters grow like crazy and I think the cooling could become an oyster farm within a month.
Looking to get either a Nordhavn or Selene and I must say I am not sold on the dry exhaust mainly because of noise (water cooled turbo with wet exhaust) and heat.
Any first hand experience would be really helpful.
Cheers,
Clive.

 

[Blissboat]

Over a period of about 15 years I ran two commercial boats with keel-cooled main engines as well as generators, all discharging through dry stacks. The waters we operated in were quite warm - 80 degrees f. in the summer, and 60 degrees f. in the winter. The cooling grids and channels were well beneath the turn of the bilge, screened from the sunlight that promotes growth. At each haulout, there was negligible fouling. Naturally, we kept up with the antifouling.

On the older of the two boats, one of the cooling grids developed a pinhole leak at a welded joint. This was after about twelve years of service. We wrapped it with gasket material and hose clamped that in place, and dealt with it at the next haulout.

As to heat, the insulation wrapped around the exhaust piping was never more than warm to the touch, even after hours of running. Noise was audible outside the boat at the point of exhaust discharge, but throughout the interior of the boat the mechanical sounds of the valve train, cylinder combustion and gearbox hum were all we heard.

These particular exhausts were rather long - approx. 25' from the manifold to discharge, and maybe that acted to reduce the sound. Even when both engines and gensets were running, it was hard to tell for sure from alongside, unless you went right around to the stern, and even then it was the pleasant odor of mostly-burned diesel fuel that confirmed things were running.

Bottom line, if designing and specifying a new-build, I would favor keel coolers and dry exhausts, absent any space conflicts or technology issues. Your concern about water-cooled turbos may qualify as a conflict, but the big Caterpillars on the workboats also had water cooled turbos and aftercoolers, all without issues.

 

[KiwiClive]

Thanks Blissboat. Very helpful

 

[guy with a boat]

Hey guys,
Does anyone here have any trouble with fouling of the keel cooling matrix?
Does the hot engine water keep the barnacles at bay?
We berth in an area where barnacles and oysters grow like crazy and I think the cooling could become an oyster farm within a month.
Looking to get either a Nordhavn or Selene and I must say I am not sold on the dry exhaust mainly because of noise (water cooled turbo with wet exhaust) and heat.
Any first hand experience would be really helpful.
Cheers,
Clive.

Our Nordhavn has a dry stack on the main (9L Deere) and wet exhaust on the wing engine (4L Deere). FWIW, the wing engine is noticeably louder than the much larger main. That tells me that, at least in our application, a dry stack doesn’t have to be noisy.

 

[sunchaser]

Some years ago we were less than enthusiastic about soot issues from an adjacent dry stack vessel. It was an old BC fisheries vessel. Two years ago another older dry stack vessel was forced to depart our marina over the same soot issue with damage money changing hands.

We had an accepted offer on a Nordhavn 55 that fell apart over ER soot, failing stack wrap and a badly sooted up exhaust chase enclosing the pipe run. Then the sea trial sooted up the upper deck area. Don't get me wrong, I love Nordhavns, but the soot issue . There are many happy wet exhaust Nordhavn owners out there.

I clearly understand dry stack on commercial vessels with highly variable load related water lines, but on a "yacht" not so much.

 

[twistedtree]

I think there is a large element of "pick your poison" in the debate between dry stack/keep cooled and wet exhaust/heat exchanger cooled. That's why the debate never ends - there is no right answer. That said, there might be a preferred answer for you. There was for me.


My first dry exhaust boat was a Nordhavn 60, and I didn't care for the dry exhaust and keel cooling for many of the reasons you note. Much has to do with the details of implementation, but I found the engine exhaust to be loud, and too loud on the flybridge to comfortably run from up there. Now I'll admit right off the bat that I really value low sound levels in machinery, so this mattered to me a lot more than it might matter to others. To Guy With A boat's comments (our boats were nearly identical WRT machinery), my wing engine was unbearably loud. It was a wet exhaust, but not really. It was a dry muffler, followed by a water injection elbow and exhaust out the side of the boat. I hated running the wing engine. GWaB may have a different arrangement, but mine was loud.


As for keel cooling, like bottom fouling, it will depend greatly on the waters you are in. I didn't have much issue with fouling, but the zincs needed replacement quite often, and that required diving on the boat. I truly hate changing impellers, but at least I can do it from inside the boat where it's dry. So I prefer the maintenance "poison" of a wet exhaust vs dry.


Also, a lot of people talk about the desire to keep sea water out of the boat when arguing for dry exhaust. But you still have plenty of sea water coming through the boat for the generator(s) and wing engine, not to mention HVAC, water makers, hydraulic cooling, etc.


For all these reasons I switched to wet exhaust on my Nordhavn 68. The boat is MUCH quieter. The only place there is exhaust noise is in the cockpit and it's barely over 70db, and is mostly boat wake noise rather than exhaust note.

 

[guy with a boat]

Sunchaser,

The N55 you mentioned had some issues beyond the norm and you were right to be concerned. We have no soot in our ER (it is clean white gel coat so soot would be hard to miss) and our dry exhaust stack is clean inside the enclosure and out. I think it would take both a poorly running engine and exhaust pipe leaks to create the mess that you describe on the 55.

Our boat is not old (2015) so the engine likely runs cleaner than older boats. We also run at higher rpms for a short period during each trip to reduce the likelihood of soot and carbon buildup. We don’t have a flybridge but I can imagine that the sound from the stack might be problematic in that situation since you would be relatively close to the outlet.

We have had wet exhausts on previous boats and I would be happy with either system. As TT says, there is more than one right answer. Both systems can be good and neither is perfect.

Just don’t assume all dry stacks must be bad because a few have problems. I see old wet exhaust boats trailing clouds of smoke, but that shouldn’t make me decide all wet exhaust boats are bad. Many more Nordhavns (as an example) have been built with dry stacks than wet exhaust, and that wouldn’t continue to be the case if the problems described above were common.

 

[Retriever]

My N50 has the typical keel cooled, dry stack arrangement for the main. I occasionally do have sooting issues. They’re annoying but quickly dealt with. Covering the stack when there’s any rain in the forecast or even heavy condensation makes a difference.

Wet exhaust boats aren’t immune to soot issues; I’ve seen plenty with big exhaust stains down the side or on the transom. They’re just a different type of soot and possibly easier to clean.

We never had a problem with the keel cooler fouling and causing overheating in the cool PNW water, but it is a problem in Mexico. Someone has to clean the keel cooler once a month, or the engine slowly overheats at very high loads.

Noise isn’t a problem for us because we don’t have a flybridge, but I’ve been on dry exhaust Nordhavns with flybridges and the exhaust sound is noticeable up there when underway.

On the plus side, the aft salon door can be open when underway because there’s no station wagon effect. There are fewer opportunities for seawater leaks and rust around the main engine. And it is comforting to not be reliant on an impeller and small, cloggable inlet for main engine operation.

On long runs, we’ve learned the exhaust stack introduces enough heat into a pantry locker to melt chocolate!

Overall I think it’s pretty close to six of one, half dozen of the other.

 

[O C Diver]

Looking to get either a Nordhavn or Selene and I must say I am not sold on the dry exhaust mainly because of noise (water cooled turbo with wet exhaust) and heat.
Any first hand experience would be really helpful.
Cheers,
Clive.

Maybe I'm misreading you, but the turbo part shouldn't change on most engines as the turbos are freshwater cooled regardless of dry stack or wet exhaust.

Ted

 

[Keysdisease]

As mentioned, and well said, pick your poison or it's six one way, half dozen the other.
All that said I believe there is no exhaust system quieter than a high quality wet exhaust system, so if quiet is the goal, wet is the way.
All the other pros and cons are valid

 

[mvweebles]

I think there is a large element of "pick your poison" in the debate between dry stack/keep cooled and wet exhaust/heat exchanger cooled. That's why the debate never ends - there is no right answer. That said, there might be a preferred answer for you. There was for me.


My first dry exhaust boat was a Nordhavn 60, and I didn't care for the dry exhaust and keel cooling for many of the reasons you note. Much has to do with the details of implementation, but I found the engine exhaust to be loud, and too loud on the flybridge to comfortably run from up there. Now I'll admit right off the bat that I really value low sound levels in machinery, so this mattered to me a lot more than it might matter to others. To Guy With A boat's comments (our boats were nearly identical WRT machinery), my wing engine was unbearably loud. It was a wet exhaust, but not really. It was a dry muffler, followed by a water injection elbow and exhaust out the side of the boat. I hated running the wing engine. GWaB may have a different arrangement, but mine was loud.


As for keel cooling, like bottom fouling, it will depend greatly on the waters you are in. I didn't have much issue with fouling, but the zincs needed replacement quite often, and that required diving on the boat. I truly hate changing impellers, but at least I can do it from inside the boat where it's dry. So I prefer the maintenance "poison" of a wet exhaust vs dry.


Also, a lot of people talk about the desire to keep sea water out of the boat when arguing for dry exhaust. But you still have plenty of sea water coming through the boat for the generator(s) and wing engine, not to mention HVAC, water makers, hydraulic cooling, etc.


For all these reasons I switched to wet exhaust on my Nordhavn 68. The boat is MUCH quieter. The only place there is exhaust noise is in the cockpit and it's barely over 70db, and is mostly boat wake noise rather than exhaust note.

TT - a few years ago you wrote similarly on this topic. I was surprised that you, a serial Nordhavn owner (a compliment), went against Nordhavn orthodoxy of dry stack.

For me, the most compelling tidbit was that maintenance could be conducted inside the boat vs needing a diver or a haul. For better or worse, there's no question about something on the outside of the boat being fouled.

I don't think it's been mentioned in this thread, but dry stacks in recreational trawlers often require a lot of air cooling of their own (well, chocolate chips melting when stored near stack-chase was mentioned). Lose the blowers and cooling is a problem.

Like so many things, it's the type of thing that would not be a deal killer either way. But the first time I read TTs thought process that led to him ordering wet exhaust, I realized there was a strong case for wet exhaust. Until then, I just assumed that functionally, dry was the way to go. Nothing wrong with either way.

Peter

 

[twistedtree]

The other big issue for us was sooting from the exhaust. I’m not talking about flakes of soot on startup. That’s a common problem, but we never had it due to a newer engine and judicious use of an exhaust pipe cover. But any diesel will leave a haze of soot that builds up over time.

With a dry exhaust, that soot covered the stack and all the instruments up there, and it was very difficult to clean. First, you need to climb the stack and hang on with one hand while cleaning with the other. Second, you need to be gentle because you are cleaning GPSes, radars, sat compasses, and other fragile stuff. Third, everything you wash off showers down on the rest of the boat forcing a complete boat was, not to mention the soot that gets all over you and your clothes. It’s a very messy job.

In contrast, washing soot off the stern quarter or transom is easy and doesn’t make a mess of the rest of the boat.

 

[rslifkin]

For me, the most compelling tidbit was that maintenance could be conducted inside the boat vs needing a diver or a haul. For better or worse, there's no question about something on the outside of the boat being fouled.

I think that alone would be enough to make the decision for me. I don't dive, so anything that reduces the risk of needing to find a diver or haul the boat to deal with an issue that I can't is a good thing in my mind.

 

[Hippocampus]

See keel coolers sitting inside a coolant bath on some Al boats. No coils exposed. See mixed systems as well with final exhaust just above waterline and water injected inside the boat so little smoke let alone soot comes out. Totally ignorant of the details. Can anyone more knowledgeable explain the details and +/- of those approaches?

 

[guy with a boat]

I think that alone would be enough to make the decision for me. I don't dive, so anything that reduces the risk of needing to find a diver or haul the boat to deal with an issue that I can't is a good thing in my mind.

We have someone dive our boat twice a year (spring and fall, unless we have a haul-out scheduled) to clean the bottom and change the underwater zincs. Our keel cooler is cleaned and the zincs on it are checked/changed at the same time. The service is required regardless, so the presence of the keel cooler doesn’t change anything.

The schedule of 2x/year works for the waters of BC and PNW. When our boat (and previous boats) have been based in warm water farther south, they got monthly hull cleanings. The diver checks/changes underwater zincs as part of that program.

It is true that the presence of the keel cooler presents another possible failure point under the water. They are tucked into a hull recess and typically are pretty trouble free outside of the maintenance mentioned above. Coolant leaks have happened at connections but are pretty rare. The risk of damage/failure is low enough that they are pretty standard on work/fish boats.

Hippo, the enclosed coils do offer even greater protection against damage and present an easier surface to clean. The tradeoff is that you lose efficiency in heat transfer so you have to upsize or otherwise manage that equation. Nordhavn’s approach has been to build the coils out of titanium and tuck them into the hull recess and that has given excellent cooling and durability.

 

[guy with a boat]

The other big issue for us was sooting from the exhaust. I’m not talking about flakes of soot on startup. That’s a common problem, but we never had it due to a newer engine and judicious use of an exhaust pipe cover. But any diesel will leave a haze of soot that builds up over time.

With a dry exhaust, that soot covered the stack and all the instruments up there, and it was very difficult to clean. First, you need to climb the stack and hang on with one hand while cleaning with the other. Second, you need to be gentle because you are cleaning GPSes, radars, sat compasses, and other fragile stuff. Third, everything you wash off showers down on the rest of the boat forcing a complete boat was, not to mention the soot that gets all over you and your clothes. It’s a very messy job.

In contrast, washing soot off the stern quarter or transom is easy and doesn’t make a mess of the rest of the boat.

TT, I’m curious as to why our experience on this point has been different. Possibly the mast and stack shape is different enough between the 60 and 63 to affect the flow of the exhaust, but I have no idea if that is a factor.

It sure seems like any buildup we get on the mast and equipment up there is pretty minimal. It is not zero either, so maybe it just bothers me less.

As I’ve said, I could be happy with either dry stack or wet exhaust, and the pros/cons are out there. Another benefit of wet exhaust is that you don’t have to dedicate space through each deck level for the stack and enclosure. That also frees up the floor plan options. Hmmm, maybe you are convincing me to look harder at wet exhaust if there is a next boat for us…

 

[twistedtree]

TT, I’m curious as to why our experience on this point has been different. Possibly the mast and stack shape is different enough between the 60 and 63 to affect the flow of the exhaust, but I have no idea if that is a factor.

It sure seems like any buildup we get on the mast and equipment up there is pretty minimal. It is not zero either, so maybe it just bothers me less.

As I’ve said, I could be happy with either dry stack or wet exhaust, and the pros/cons are out there. Another benefit of wet exhaust is that you don’t have to dedicate space through each deck level for the stack and enclosure. That also frees up the floor plan options. Hmmm, maybe you are convincing me to look harder at wet exhaust if there is a next boat for us…

Not sure if yours has one, but the later 63s have an extension pipe on the exhaust that directs the plume further aft and away from the stack and instruments. I think that was a good addition, and I was considering such a retrofit on my 60.


I think with any of these systems you can do a good job designing and building it, or you can do a not-so-good job. As an example, I had a wet exhaust boat a while back that was so loud at the helm that my wife and I always used ear plugs. So wet exhaust itself doesn't solve all noise problems.

 

[ak-guy]

I should have taken a photo but at haulout a few weeks ago my keel cooler was thick with barnacles and mussels. The rest of the hull was clean. My keel cooler is about 16' of copper pipe and I had painted it with antifoul in the spring. The pipe was so fouled that the cooling was impaired. The only thing I suspect is that the pipe is old and has a rough surface allowing things to attach to it. I plan to go at it with a brass brush in a drill.

 

[Circumnavigator]

Fintry has a dry exhaust on the main with heat exchanger cooling. We did it that way on the advice of our naval architect, who said it would be much quieter. The muffler is very large, hidden in Fintry's funnel, and it is, indeed, very quiet. You can't hear it running inside the boat.



The only time we have had a significant soot problem was after 2,000 hours when the air cleaner needed cleaning.


Jim

 

[Hippocampus]

Could you supply details Jim. Apologize for my ignorance.

 

[Retriever]

Not sure if yours has one, but the later 63s have an extension pipe on the exhaust that directs the plume further aft and away from the stack and instruments. I think that was a good addition, and I was considering such a retrofit on my 60.


I think with any of these systems you can do a good job designing and building it, or you can do a not-so-good job. As an example, I had a wet exhaust boat a while back that was so loud at the helm that my wife and I always used ear plugs. So wet exhaust itself doesn't solve all noise problems.

Previous owners of my boat added an ~18" extension to the stack to get the exhaust further away from the sat compass. The electronics up there stay clean enough that I've never bothered to go up to the top of the mast to clean them. I don't have big satellite domes up there which might have a tendency to look dirtier than a small satellite compass.

 

[N4061]

Experience

I owned two N40's (Lugger dry stack exhaust), one N35 (Yanmare, wet exhaust) and one Helmsman 38 (Cummins wet exhaust).

Compared to the Yanmare the Lugger was quieter inside the boat. Compared to the Yanmare and Lugger the Cummins was quieter).

I believe its not so much the engine or dry / wet exhaust "but" the quality of the boat including insulation around the ER. The sound inside the ER with the Lugger was definitely louder (going by memory) but my responses above are inside the boat with the ER door shut tightly.

Suggest you try and get aboard the different boats you are interested in and listen while cruising then you can make your own decision.

John T.

 

[Circumnavigator]

Could you supply details Jim. Apologize for my ignorance.

I'm not sure what detail you want, so feel free to ask for more.


You can't see the funnel in the photo to the left, so go to http://www.mvfintry.com/pix/watertanks.jpg to see the large funnel. (The image is from just after we bought her and shows the two tanks which originally provided potable and seawater pressure for domestic use and toilet flush.)



The exhaust comes out of the turbo, wrapped in a heavy blanket and goes straight up through a large muffler that fills most of the funnel and then goes out through an inverted ell that doesn't show in the drawing. The blanket covers it all the way up and is at ambient temperature to the touch. The pipe and muffler are supported by steel brackets in two places on the way up. The brackets come through the blanket and are hot -- maybe 200F. The brackets are bolted to vibration isolators which are, in turn, bolted to brackets that are welded to a nearby bulkhead. (The CAT 3406 is on soft mounts, hence the need for soft mounts on the exhaust.).


The cooling water comes in through a sea chest, goes through the heat exchanger, and goes overboard to starboard about six inches above the waterline.


Jim

 

[guy with a boat]

Not sure if yours has one, but the later 63s have an extension pipe on the exhaust that directs the plume further aft and away from the stack and instruments. I think that was a good addition, and I was considering such a retrofit on my 60.

I think that is probably a big factor. Our exhaust pipe extends pretty far back from where it exits the mast.

I just took a quick look at line drawings of both boats and the mast on the 63 also extends farther above the pilothouse roof than the mast of the 60 does above the FB hardtop. That may well allow enough more air flow at the exhaust point to carry away any soot rather than allow it to accumulate.

It all circles back to your point that details of design and construction are just as important as which exhaust system is chosen.

 

[Keysdisease]

There is a reason most Cruise Ships have some version of this stack

 

[Ric]

We have a hybrid arrangement with a keel cooler and a wet exhaust. It worked perfectly in the Pacific NW. In New Zealand it has been iffy; the rate of fouling is almost unbelievable. In 4 months, I could be a mobile oyster farm. I've tried painting with antifoul; good for 5 months. I then tried bare bronze pipes; good for 5 months. Now I've applied PropSpeed and am hoping for better luck. We'll see how the summer goes, as the water warms and growth accelerates. I do like not having to deal with flushing and cleaning heat exchanger tubes. On the other hand, the hybrid setup has the disadvantage of still needing a raw water pump and a temperature alarm on the injection port.
When we bought the unfinished boat the wet exhaust was already set up, so a dry stack wasn't in the cards. It was set up for a keel cooler using the boxed keel, but that was inadequate for the Cummins we installed so we sealed off those pipes and put in a Walter keel cooler.
For temperate and higher latitude cruising, I'd go with a dry stack if there's a good routing. For tropical climes, it'd be fine in a boat large enough to insulate it thoroughly. That could be a problem in a small cruiser. We had a 43' with a diesel stove that was great in the NW but even with the stack well insulated it was a nightmare in Hawaii.
Cheers,
Ric

 

[chriscritchett]

What many fail to realize is that most keel coolers are made from a copper alloy. Copper is / used to be the active ingredient in most antifouling paints.

I have a homemade copper tubing cooler under the boat in my avatar, and when left bare in the high fouling waters of SWFL it never had more than a bit of discoloration on it. When a boatyard stupidly painted it and I didnt get ALL the residue off, growth attached itself to what was left of the paint and I had to strip it at next haulout.

No direct experience with the copper-nickel material used in hi-$$ coolers, but I believe they would be pretty fouling free if left to their own devices as well.

As to the rest of the debate, have fun with it. My boat had no generator and no toilet overboard, so ZERO thru-hulls aside from the shaft log. I loved that. But, such simplicity is not for everyone.

If I were to have my (displacement speed) dream boat, I would carry that concept on to the genset and HVAC / refrigeration, too. There is no reason all that stuff can’t be keel-cooled, but it’s outside the recreational mainstream and therefore harder to do.

 

[DaveS]

Perhaps it’s the boat? I have no noise issue with out Nordhavn 55 (N55-40) even on the fly bridge. The wing is much noisier. The keel cooler is however a pain to keep clean especially in warm water and our main (a JD 6081) runs significantly hotter if the keel cooler is not properly maintained. Still, I like the closed loop system and would keep the dry stack even if I could afford a 68!

 

[Ric]

What many fail to realize is that most keel coolers are made from a copper alloy. Copper is / used to be the active ingredient in most antifouling paints.

I have a homemade copper tubing cooler under the boat in my avatar, and when left bare in the high fouling waters of SWFL it never had more than a bit of discoloration on it. When a boatyard stupidly painted it and I didnt get ALL the residue off, growth attached itself to what was left of the paint and I had to strip it at next haulout.

No direct experience with the copper-nickel material used in hi-$$ coolers, but I believe they would be pretty fouling free if left to their own devices as well.

.

The Walter Keel Coolers are $$ and some copper alloy, which is why I tried leaving it bare after blasting it clean. Overgrown only a little bit slower than with bottom paint.