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Old 10-21-2018, 07:53 AM   #21
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Not to forget, keel cooling and dry stack are pretty much tied together. On commercial vessels wet exhaust is negated by a changing water line related to load submergence.

I struggle with advantages of keel cooling on a non commercial vessel built for purely recreational purposes and based upon trial and error design and setups.

Dry stack on yacht finishes, bridge enclosures and teak decks is seldom appreciated due to soot. We did did not close on a dry stack vessel a few years ago, one of the reasons being intentional overpropping and resultant soot damaging the finish, vessel interior and enclosures. The owner insisted that all was ok and he wouldn't spring for fixes.
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Old 10-21-2018, 09:00 AM   #22
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"On all the keel cooled boats I've seen, there is only the normal thermostat that is integral to the engine. It causes coolant to circulate within the engine, and divers only as much to the keel cooler loop as is needed to maintain proper engine temp. It's no different than regulating the portion of coolant that flows to a radiator, or the portion that flows through a heat exchanger for a sea water cooled engine."

The problem is a keel cooler is designed to work in the extreme. Tropics, heavy load , slightly fouled .

When coolant is released to a radiator the return water to the engine is only about 20-30deg below the engines operating temperature. Trucks cover most of the radiator in really cold weather to maintain the radiator temperature. A keel cooled boat may have the cooler in 40f or 50F water so the return temperature can be over 120f colder than the circulating water.

A just started cold engine mostly warms up as a unit.

An engine with a constant over 100deg difference in the departing coolant and the return coolant can experience a thermal shock that will have the block distorted , and all the precision machining is for naught.

The engine will survive , but there will be a higher fuel bill and some service life lost.

A bypass thermostat is cheap insurance for engine longevity as well as more constant heat that can be used to heat crew quarters , FW supply and warm the hand rails and a drying hanging locker..


Well, I have to disagree. I know of many boats with keel cooling as I describe, which is also how cummins, deere, Scania, DD/MTU, and I’m sure many others tell you to do it. And they have thousands of hours on them, many 10k plus. It’s all in how much of that cooler coolant circulates back in. A small quantity mixed right away, brings the temp down to the target operating temp, and all is good. I have personally operated for extended time at idle or close to it, surrounded by ice in water in the 30s, and engine temp holds just fine.
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Old 10-21-2018, 09:40 AM   #23
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"It’s all in how much of that cooler coolant circulates back in."


Exactaly , the least expensive system simply use a leaky engine thermostat , a std unit with either a cut out section , or a hole or two drilled .
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Old 10-21-2018, 09:58 AM   #24
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If you take an engine and adapt it to keel cooling, there can be some strange temperature dynamics. There is a much larger volume of cool coolant residing in the cooler than you would see in a radiator or HX type system. As a result the thermostat may cycle open and closed causing engine temps to swing. Usually no harm, but not desirable.

But many engines are designed for keel cooling and their temp control system can handle it.

If you buy a road tractor engine and hook it up, weirdness can happen. I've had to troubleshoot a few, and was successful.

The magic of keel cooling and dry exhaust is that you CAN use a road tractor or any other type of engine. It won't even know it is in a boat!!
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Old 10-21-2018, 11:54 AM   #25
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Sure. But exposed protruding pipes?
Makes me a bit nervous. Delfin was built with half pipe keel coolers port and starboard, which I now use to cool hydraulics and a/c. Walter keel coolers now take care of the genset and main. I guess the advantage of just hanging the pipes is that you don't have the very long welded seams which require a lot of weld grinding to meet current standards of how steel boat welds underwater should be prepped for barrier coating, and half the length required. I am in the process now of sand blasting her to remove 18 years of build up and you can see that the half pipes have taken a beating in places over the years. Whether any of the dings visible would have dislodged hung pipes is hard to say, but I would feel better with that arrangement if there were protective fins that diverted logs, shipping containers, etc. away from the pipes. I also would not be wild about the drag imposed by these. All in all it seems a pretty third world way of doing things. FYI, the Walter keel coolers on Delfin are all protected by flat steel on one side and rolling chocks on the other.

I would also point out that to cool Delfin's original 250 hp Volvo, the Norwegian fellars welded on 180' of 2" half pipe. I have no idea if this was an engineered installation or "run of thumb", but since those folks had been building fishing boats for around 150 years, I assume they knew what they were doing.
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Old 10-21-2018, 12:09 PM   #26
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"On all the keel cooled boats I've seen, there is only the normal thermostat that is integral to the engine. It causes coolant to circulate within the engine, and divers only as much to the keel cooler loop as is needed to maintain proper engine temp. It's no different than regulating the portion of coolant that flows to a radiator, or the portion that flows through a heat exchanger for a sea water cooled engine."

The problem is a keel cooler is designed to work in the extreme. Tropics, heavy load , slightly fouled .

When coolant is released to a radiator the return water to the engine is only about 20-30deg below the engines operating temperature. Trucks cover most of the radiator in really cold weather to maintain the radiator temperature. A keel cooled boat may have the cooler in 40f or 50F water so the return temperature can be over 120f colder than the circulating water.

A just started cold engine mostly warms up as a unit.

An engine with a constant over 100deg difference in the departing coolant and the return coolant can experience a thermal shock that will have the block distorted , and all the precision machining is for naught.

The engine will survive , but there will be a higher fuel bill and some service life lost.

A bypass thermostat is cheap insurance for engine longevity as well as more constant heat that can be used to heat crew quarters , FW supply and warm the hand rails and a drying hanging locker..
I have always had a hard time understanding the thermodynamic benefits of a bypass thermostat. On my boat, there isn't one and I never see the slightest change in operating temps at a given rpm. The range across all rpms is about 10 degrees - 180 to 190 degrees. If the water entering the water pump had a delta of 100 degrees, the stat is open 'x'. If it has a delta of 20 degrees the stat is open 'x' plus. In both cases, the water that circulates through the engine is at the temperature of the thermostat isn't it? And doesn't the water pump do a pretty good job of blending incoming cold coolant with returning hot coolant from the water jacket? Not arguing against a bypass, just wondering how it helps.
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Old 10-21-2018, 12:15 PM   #27
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Not to forget, keel cooling and dry stack are pretty much tied together. On commercial vessels wet exhaust is negated by a changing water line related to load submergence.

I struggle with advantages of keel cooling on a non commercial vessel built for purely recreational purposes and based upon trial and error design and setups.

Dry stack on yacht finishes, bridge enclosures and teak decks is seldom appreciated due to soot. We did did not close on a dry stack vessel a few years ago, one of the reasons being intentional overpropping and resultant soot damaging the finish, vessel interior and enclosures. The owner insisted that all was ok and he wouldn't spring for fixes.
Tom, I think the amount of soot depends on the engine and how it's used. I've moored next to fishing boats running their engines 24 x 7 and had to move from the cloud of soot they produced. Our 3306 dry stack seems to produce very little, although I do get a build up of exhaust black on the mizzen, but rarely any flecks of soot. The mizzen cleans up just fine. The one thing I do that may help a lot is run the engine up to 80% full power for 15 minutes or so before cooling down for anchoring or mooring. That gets the EGT up to 775 and seems to blow any chunks present into the wind.
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Old 10-21-2018, 01:28 PM   #28
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I have always had a hard time understanding the thermodynamic benefits of a bypass thermostat. On my boat, there isn't one and I never see the slightest change in operating temps at a given rpm. The range across all rpms is about 10 degrees - 180 to 190 degrees. If the water entering the water pump had a delta of 100 degrees, the stat is open 'x'. If it has a delta of 20 degrees the stat is open 'x' plus. In both cases, the water that circulates through the engine is at the temperature of the thermostat isn't it? And doesn't the water pump do a pretty good job of blending incoming cold coolant with returning hot coolant from the water jacket? Not arguing against a bypass, just wondering how it helps.

I think for any marinized engine, it's just not an issue. A bypass would only be needed if the thermostat on the engine was not up to snuff. Consider that the exact same issue exists with a truck in extreme cold. The coolant in the radiator is cold as a witches tit, especially during warm up, and mixes just fine with the rest of the coolant.
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Old 10-21-2018, 01:34 PM   #29
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Tom, I think the amount of soot depends on the engine and how it's used. I've moored next to fishing boats running their engines 24 x 7 and had to move from the cloud of soot they produced. Our 3306 dry stack seems to produce very little, although I do get a build up of exhaust black on the mizzen, but rarely any flecks of soot. The mizzen cleans up just fine. The one thing I do that may help a lot is run the engine up to 80% full power for 15 minutes or so before cooling down for anchoring or mooring. That gets the EGT up to 775 and seems to blow any chunks present into the wind.

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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Old 10-21-2018, 01:43 PM   #30
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I think for any marinized engine, it's just not an issue. A bypass would only be needed if the thermostat on the engine was not up to snuff. Consider that the exact same issue exists with a truck in extreme cold. The coolant in the radiator is cold as a witches tit, especially during warm up, and mixes just fine with the rest of the coolant.
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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Old 10-21-2018, 01:48 PM   #31
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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.
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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Old 10-21-2018, 02:50 PM   #32
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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.

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.
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Old 10-21-2018, 02:54 PM   #33
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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.



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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Old 10-21-2018, 03:05 PM   #34
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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.
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.
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Old 10-21-2018, 03:09 PM   #35
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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.

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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Old 10-21-2018, 03:26 PM   #36
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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.

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.
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Old 10-21-2018, 03:36 PM   #37
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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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Old 10-21-2018, 03:49 PM   #38
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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?

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.
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Old 10-21-2018, 03:53 PM   #39
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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?

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.
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Old 10-21-2018, 04:06 PM   #40
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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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