Keel Cooling - Split pipe versus external pipe

twistedtree said:

Hand in hand with switching to sea water cooling, we are switching back to wet exhaust. Like you, we never had soot flakes, but we did get a coating of soot buildup around the exhaust exit. It covered all the instruments, and looked like hell. And cleaning was a major pain in the butt./ I had to climb up on the hard top, then climb the stack, and hand scrub every instrument and every branch of the tree. And all the scrum and rinse water showered down on the rest of the boat, covering it in black sooty water, necessitating a complete wash of the boat. Wet exhaust soots too, but it's MUCH easier to clean a transom and sides of the boat than to climb the stack, hand scrub everything, then the whole rest of the boat.... Never again. To me, dry stack and keel cooling was a big mistake that I won't make again.

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I have both. The CAT is dry stack keel cooled, the genset is keel cooled, but raw water exhaust through a lift muffler. Personally, cleaning the dry stack exhaust residue is easier than cleaning the black film all along the waterline from the genset exhaust, but to each his own. I just like the fact that there is zero maintenance on a keel cooled, dry stack setup other than cleaning which I do anyway. No zincs, no raw water, no raw water pumps, no exchangers, no impellers, no nothing. Just start and go.

Delfin said:

I guess I'm not sure what a marinization means for a dry stack, keel cooled engine. You could take my CAT out and stick it in a bulldozer.

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I'm not familiar with Cat details, but on Deere and Cummins, there are quite a few differences. Header/expansion tanks, jacketed exhaust manifolds, jacketed turbos, gear coolers, after coolers, to name a few. Jacketed manifolds and turbo are probably the most significant, greatly reducing the heat rejection into the ER.


So by "Marinized engine" I guess I just mean an engine where the designers have at least considered a marine application and made any necessary adjustments. The only reason I can see to require an external thermostatic bypass is if the engine's own cooling system isn't up to the task, like a tractor engine stuffed in a boat as Ski describes.

Delfin said:

I have both. The CAT is dry stack keel cooled, the genset is keel cooled, but raw water exhaust through a lift muffler. Personally, cleaning the dry stack exhaust residue is easier than cleaning the black film all along the waterline from the genset exhaust, but to each his own. I just like the fact that there is zero maintenance on a keel cooled, dry stack setup other than cleaning which I do anyway. No zincs, no raw water, no raw water pumps, no exchangers, no impellers, no nothing. Just start and go.

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Those are indeed the benefits.


No zincs or cleaning required on your keel coolers? Mine were about every 6 months, and obviously a go-swimming operation. Personally I'll trade that for an impeller change once a year, and a heat exchanger cleaning every few years. But that's just me.

twistedtree said:

Those are indeed the benefits.


No zincs or cleaning required on your keel coolers? Mine were about every 6 months, and obviously a go-swimming operation. Personally I'll trade that for an impeller change once a year, and a heat exchanger cleaning every few years. But that's just me.

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Yes, you're right on the cooler zincs - forgot about those. I have them changed every six months with a light scrub by a diver. But no cleaning as they seem to stay clean by themselves. And you're also right on the jacketed exhaust and turbo, which mine has for the reasons you state.

twistedtree said:

Those are indeed the benefits.


No zincs or cleaning required on your keel coolers? Mine were about every 6 months, and obviously a go-swimming operation. Personally I'll trade that for an impeller change once a year, and a heat exchanger cleaning every few years. But that's just me.

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OK, you are talking me into a raw water cooling system.....but only if it wont decrease engine life. Are you in salt water (marine) or in fresh water? I think a salt water cooled engine suffers from a shorter lifespan...or am I wrong. AND would it not still require an impeller change regularly. The water wont just jump up into the engine will it.

jimisbell said:

OK, you are talking me into a raw water cooling system.....but only if it wont decrease engine life. Are you in salt water (marine) or in fresh water? I think a salt water cooled engine suffers from a shorter lifespan...or am I wrong. AND would it not still require an impeller change regularly. The water wont just jump up into the engine will it.

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Salt water. But do keep in mind that the salt water doesn't run through the engine. It runs through a heat exchanger only. Regular coolant runs through the engine, and the heat exchanger. The heat exchanger is just a radiator that is cooled by running sea water over it rather than forced air. And a keel cooler is just a radiator that is dipped in the ocean.


I don't think you will see any difference in life span assuming good maintenance on both types of engines. I know many people with over 10,000 hrs on both types of installations.


Noise level is another consideration. Lots depends on the specifics of a particular boat, but I generally find wet exhaust quieter than dry.

You misunderstood my post. I said "raw water cooled". I currently have the heat exchanger cooled system. I can understand raw water cooling if you are in fresh water but I am in a marine environment. I will go to the simpler system of raw water cooling if it wont hurt my engines lifespan.


I guess I misunderstood you when you said you would trade zincs on the bottom for an impeller change I thought you were arguing FOR raw water cooling as you preferred swimming to mechanical work on the pump.


I guess I dont see why you cannot have a wet exhaust with a raw water cooling. Its just a matter of plumbing?

jimisbell said:

You misunderstood my post. I said "raw water cooled". I currently have the heat exchanger cooled system. I can understand raw water cooling if you are in fresh water but I am in a marine environment. I will go to the simpler system of raw water cooling if it wont hurt my engines lifespan.


I guess I misunderstood you when you said you would trade zincs on the bottom for an impeller change I thought you were arguing FOR raw water cooling as you preferred swimming to mechanical work on the pump.


I guess I dont see why you cannot have a wet exhaust with a raw water cooling. Its just a matter of plumbing?

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So many words and so many meanings.... By "raw water cooling" and "heat exhanger cooling" I meant the same thing. With semi-modern engines, I think that's true, but it hasn't always been. For a while there were engines that ran sea water right through the engine, but I think all pretty quickly figured out that it was a bad idea and stopped. Outboards would be the only exception I can think of, but maybe someone else can come up with others.


Personally I would never even consider running raw water, whether salt or fresh, straight through the engine.

jimisbell said:

You misunderstood my post. I said "raw water cooled". I currently have the heat exchanger cooled system. I can understand raw water cooling if you are in fresh water but I am in a marine environment. I will go to the simpler system of raw water cooling if it wont hurt my engines lifespan.


I guess I misunderstood you when you said you would trade zincs on the bottom for an impeller change I thought you were arguing FOR raw water cooling as you preferred swimming to mechanical work on the pump.


I guess I dont see why you cannot have a wet exhaust with a raw water cooling. Its just a matter of plumbing?

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Oh, and I'm arguing FOR heat exchanger cooling over keel cooling because I prefer to change impellers and clean heat exchangers inside the boat, over going swimming to change zincs and clean a keel cooler.

TT you make a point on wet exhaust and necessary hull cleaning. On my wet exhaust systems, both genset and twin mains, I have zero soot buildup on the boat hull. I am not alone. All sorts of reasons for this I would guess. One reason proposed by many is lots of boat wax. Others could be water lift mufflers, not over propped and keeping RPM near max torque range.

sunchaser said:

TT you make a point on wet exhaust and necessary hull cleaning. On my wet exhaust systems, both genset and twin mains, I have zero soot buildup on the boat hull. I am not alone. All sorts of reasons for this I would guess. One reason proposed by many is lots of boat wax. Others could be water lift mufflers, not over propped and keeping RPM near max torque range.

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I have a gas/air separater on the genset that probably contributes to the soot buildup I see.

Delfin said:

I have a gas/air separater on the genset that probably contributes to the soot buildup I see.

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Interesting. Why do you think it impacts the soot buildup?

twistedtree said:

Interesting. Why do you think it impacts the soot buildup?

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The water goes out below the waterline, and just the gas above. My assumption is that if water was mixed with the gas above the waterline there might be less in the way of solids deposited on the hull.

Keel coolers on a friend's 80' ex fishboat:

twistedtree said:

Hand in hand with switching to sea water cooling, we are switching back to wet exhaust. Like you, we never had soot flakes, but we did get a coating of soot buildup around the exhaust exit. It covered all the instruments, and looked like hell. And cleaning was a major pain in the butt./ I had to climb up on the hard top, then climb the stack, and hand scrub every instrument and every branch of the tree. And all the scrum and rinse water showered down on the rest of the boat, covering it in black sooty water, necessitating a complete wash of the boat. Wet exhaust soots too, but it's MUCH easier to clean a transom and sides of the boat than to climb the stack, hand scrub everything, then the whole rest of the boat.... Never again. To me, dry stack and keel cooling was a big mistake that I won't make again.

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Are other Nordhavn new build owners also choosing a wet exhaust?

I have seen a couple of Nordhavn boats with wet exhaust, and one with twin engines. They are rare birds though.

O C Diver said:

Much prefer half pipe or angle welded to the hull. The differences in my opinion are:

No hangers to fail
No need to zinc as it's one with the hull
Lower profile and nothing gets caught between it and the hull
Easier to clean on land or by a diver
IMO, less likely to be broken if you accidentally hit something
...

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What OC said.

One could also use U or square tube instead of round pipe to get more surface area.

Professional Boat Building magazine has articles on keel cooling and dry stacks that might be of interest. The index to their back issues, and a link to the back issues, are on this page, Subject Index - Professional BoatBuilder Magazine https://www.proboat.com/subject-index/

Issue No 111, Feb/march 2008 has part 1 of a two part series on Dry Exhausts and Keel Cooling. It is by Gerr.

There is quite a bit of information in the article including the calculations needed to design a keel cooler.

Per Gerr,

Keel coolers for STATIONARY operation should be mounted on the side of the hull or the keel, not horizontally under the bottom of the boat. That's because warm water will not flow away by convection but will be trapped under the cooler, which will result in overheating.

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Gerr mentions commercial coolers as well as creating recesses in the hull for their placement or keel boxes, I wonder how the heck those areas get cleaned...

Later,
Dan

stubones99 said:

I have seen a couple of Nordhavn boats with wet exhaust, and one with twin engines. They are rare birds though.

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Not really. I don't know the statistics, but there are quite a few wet exhaust Nordhavns. All the twin engine boats except one that I'm aware of. And quite a few singles as well. A wild guess would be 20% of the fleet, maybe as much as 30%. I know of three single engine, wet exhaust boats in build right now.

koliver said:

Keel coolers on a friend's 80' ex fishboat:

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I am so glad I don’t have to scrape and repaint that system.
Just my eelgrass strainers took a lot of work.

MOJO has a half-pipe keel cooler and is a dry stack exhaust. The original engine was a Cat D-13000, but was replaced in 1989 by a Cummins 5.9 6BTA-M1. The water pump in the Cummins is too small to move the volume of water in the keel cooler. The solution is to either run an off-engine pump for keel cooling or put a heat exchanger on the engine. The heat exchanger is the route the previous owner took and it works fine. The exhaust is still dry stack so there's no exhaust mixing elbow and no wet muffler. Here's a picture of the half pipe keel cooler. By my calculations, the 4 half pipes have a capacity of about 150 gallons!

That is a HUGE 1/2 pipe cooler. 6"?



But your comment about the size of the pump mystifies me. Since it is a closed system, the size of the pump is not of any concern. There is no "head" in a closed system. No lift. As long as the pump can handle the volume over time that the engine needs, and it can because it was designed for that engine, it is big enough.

That was my initial thought as well, but it turns out that a small pump pushing against a large volume of water apparently ends up creating a laminar flow that isn't efficient in dumping the heat. (I never took fluid dynamics or thermodynamics so I don't know for sure!) The previous owner (who pulled out the Cat & put in the Cummins) said they tried it and found the engine would overheat. Cummins told him that he would need to install a higher volume off-engine pump if he wanted to use the half-pipe keel cooler. The easy solution was to use the heat exchanger that came with the engine.

I don't remember for sure, but I think they're 8" dia pipes about 16' long.

Using an onboard heat exchanger seems superfluous to me. Since the keel cooler IS a heat exchanger. So you have two pumps, one to circulate the coolant in the keel cooler and another to circulate the coolant in the engine and the boats movement thru the water circulates the real coolant over the 1/2 pipe heat exchanger?

It all does seem odd. And wow, that must be quite a bill to replace the coolant.

The keel cooler isn't being used, it isn't even plumbed anymore into the engine cooling circuit. The engine is cooled only by it's own raw water pump and it's heat exchanger. Easier and less trouble prone than worrying about a large off-engine pump. I have two spare engine raw water engine cooling pumps on-board and it's two bolts & two hose clamps to swap them out. If I were really bored and looking for a project (I'm not!), I'd plumb my 3 air conditioners into the keel cooler and be able to use fresh water for the a/c circuits. I have a 30 gpm pump for the air conditioners so I'm sure it would work fine. However, there's always ramifications of changing things! In addition to the air conditioner cooling, I use the a/c pump as a boost pump for my 33 gph watermaker. If I dedicate that pump to running the a/c's through the keel cooler, I'd have to get a new boost pump for the watermaker. Much simpler to leave things the way they've worked flawlessly for the past 18 years! It's a nice simple solution, no need for further complication.

Yes, if it aint broke, dont fix it.

jimisbell said:

That is a HUGE 1/2 pipe cooler. 6"?



But your comment about the size of the pump mystifies me. Since it is a closed system, the size of the pump is not of any concern. There is no "head" in a closed system. No lift. As long as the pump can handle the volume over time that the engine needs, and it can because it was designed for that engine, it is big enough.

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JB
You likely know this. A keel cooler does indeed increase the total head the pump sees. There are two components. Static Head and Friction Head. By increasing the pipe length dramatically the FH loss increases likewise.