Keel Cooling - Split pipe versus external pipe

My builder installs external pipes for keel cooling, as opposed to split pipe which is commonly seen in the industry as well. This will be for a single engine/keel boat (not the twin as pictured). Since the pipes would be tucked in next to the keel anyway, is there any really big detriment? It seems that risk of damage is low. How about barnacle/marine growth, etc.?

Virtually every commercial boat on the planet is keel cooled - it works.

Sure. But exposed protruding pipes?

Lots of boats have exposed tubes. Usually they run parallel to and close to the keel. I had them on a commercial boat and never heard of any tubes being damaged. They usually have a protective barrier in front to protect the tubes from debris in the water. Others build in an indent so the tubes are inset into the hull.

The only issue I had with tubes was idling at the dock in warm water too long. With no water movement the tubes make a volume of hot water and the engine can get too warm.

makobuilders said:

Sure. But exposed protruding pipes?

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There is a lot more to the design of a keel cooling system than hanging some pipes from the boat bottom. Issues such as coolant expansion, coolant volume vs grid design, corrosion, exterior water flow, pump maintenance, low speed operation, paint spec, ease of exterior cleaning etc.

Mako, I trust you've visited the websites for Walter, Duramax and Fenstrum for design tips?

Have seen all shapes, sizes and designs of keel coolers.....

Closest thing to just "totally exposed" pipes was an aluminum crew boat I ran where the coolers were a LOT of 90 degree heavy duty angle welded to the bottom of the hull to form small channels.

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


The one big downside is that welded would be much tougher to replace. Very important to keep the hull well zinced and coolant well maintained with antifreeze (rust inhibitor).

Ted

OC, I tend to agree with you. Thanks

I don't understand what you mean by "split pipe".



Here's an example of a Fernstrum grid cooler in a recessed pocket for protection. I've heard of boats with inadequate cooling when run at full power, so pay careful attention to engineering it properly. A guy with a welder is probably not the person to design and size the cooling system.

The nicest is when a box is created inside the hull with barriers to flow the water back & forth to create enough contact area for the coolant.

This will not be damaged by most anything and is no extra drag although it must be larger than normal to make up for fouling in the tropics.

A bypass thermostat is required to keep the engine coolant inlet temperature stable , usually about 20-25f below the engines operating temp.

This allows the engine thermostat to keep the desired operating temps , with no internal hot or cold spots , and no cold shock.

The box is insulated so it does not add heat to the ER or a cabin.

FF said:

The nicest is when a box is created inside the hull with barriers to flow the water back & forth to create enough contact area for the coolant.

This will not be damaged by most anything and is no extra drag although it must be larger than normal to make up for fouling in the tropics.

A bypass thermostat is required to keep the engine coolant inlet temperature stable , usually about 20-25f below the engines operating temp.

This allows the engine thermostat to keep the desired operating temps , with no internal hot or cold spots , and no cold shock.

The box is insulated so it does not add heat to the ER or a cabin.

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I'm not sure I'm visualizing the box correctly, but keep in mind that keel coolers foul just like the underside of your boat, and can lose quite a bit of their effectiveness as a result. They need to be cleaned just like the boat bottom, so accessibility is important. Interestingly, Fernstrum says not to put bottom paint on the grid because it will impede heat transfer. Makes sense, but without anti fouling paint the accumulated marine growth impedes heat transfer as well. So which is worse? MV Dirona has experimented with this and found things worked better on their boat using anti fouling on the grid cooler. But YMMV,


I'm not sure I'm following the bypass thermostat comment either. 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.


And last but not least, having had sea water cooled engines, then a keel cooled engine, I am now going back to sea water cooled. Both require maintenance, each in it's own way, so I see that as pretty much a wash. The big difference is that the maintenance on a sea water cooled engine is performed inside the boat, where on a keel cooled engine it's performed overboard, in the water. I'll take inside any day.

My entire keel is the cooler.

I like the idea of split pipe or channel welded to the hull to form a channel. I worked on one that used like 4" x 1" C-channel welded to bottom steel on outside. Man that thing held a LOT of coolant. It can also be done from inside the hull, but the heat transfer numbers will be different with more area needed.

Only downside of this is that is a LOT of welding, and every inch of weld must be absolutely leak free. No fun having a pinhole and contaminating 30gal of coolant.

For a trawler, I don't think you need to worry about low speed or dockside ops. Not like a tug where it needs to handle high power and almost zero speed.

I'd have no problem with full pipe supported next to a keel sort of in the corner. Pretty safe there. Not that hard to clean. Can also tie to a dock and run engine in gear pretty hard and cook the barnacles!!

All of the above are assuming metal hull that can be welded to. I have seen lifeboats (Fiberglass) on cruise ships that also have "Keel" cooling. Of course they hang dry all their lives, hopefully.


They are fully exposed, no protection.

Mako,
This is likely overkill, especially when in the hands of someone like me, but here is a picture of how the keel cooling was designed on Libra.
Lots of welding and lots of coolant for sure, but pretty secure in 6mm steel. You get massively stable cooling and the side benefit, I expect, of adding a little stabilization to motion when cruising.
The power plant is a commercial duty v10 Mercedes that I think is designed to run pretty continuous in the 50-90% full power range as in a long haul truck or ag equipment. She works hard pushing 63 tons thru the water. From idle to pegged, I have never seen engine oil temp vary more than one degree from 79C.

I wish I knew more about what was inside here. The whole surface steams evenly and temp seems very even to the touch when the boat is hauled after a cruise, but I assume the box is protecting pipes rather than full of coolant.

twistedtree said:

I don't understand what you mean by "split pipe".

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It's pipe that's cut in half lengthwise. When welded to the boat, it looks like half the pipe is on the outside of the hull and the other half would be inside. Lots of welding, but the pipe and hull form a 90 degree angle, making for an easy weld.

Ted

O C Diver said:

It's pipe that's cut in half lengthwise. When welded to the boat, it looks like half the pipe is on the outside of the hull and the other half would be inside. Lots of welding, but the pipe and hull form a 90 degree angle, making for an easy weld.

Ted

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Got it, thanks.

"I am now going back to sea water cooled."


The usual problem with direct sea water cooled , no second pump and heat exchanger, is engine service life till rusting out.

Also the engine is usually operated quite cool (under 140F) to keep salt from coming out of solution and blocking passages.

"I'm not sure I'm visualizing the box correctly, but keep in mind that keel coolers foul just like the underside of your boat, and can lose quite a bit of their effectiveness as a result."

A channel of metal is created inside and the coolant is against the inside of the hull.

A bolted cover seals the passages creating a "pipe" for the coolant.

All work is inside the vessel, although the hull will foul under the passages due to growth enjoying the temperature.

There is nothing outside but hull.

FF said:

"I am now going back to sea water cooled."


The usual problem with direct sea water cooled , no second pump and heat exchanger, is engine service life till rusting out.

Also the engine is usually operated quite cool (under 140F) to keep salt from coming out of solution and blocking passages.

"I'm not sure I'm visualizing the box correctly, but keep in mind that keel coolers foul just like the underside of your boat, and can lose quite a bit of their effectiveness as a result."

A channel of metal is created inside and the coolant is against the inside of the hull.

A bolted cover seals the passages creating a "pipe" for the coolant.

All work is inside the vessel, although the hull will foul under the passages due to growth enjoying the temperature.

There is nothing outside but hull.

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Thanks for the clarification.


I think direct sea water cooled engines are pretty much extinct at this point, aren't they? For those unsure of the difference, a direct sea water cooled engine is where the seawater circulates through the engine's cooling jackets. This is on contrast with a heat exchanger engine where coolant circulated through the engine, and there is a coolant to sea water heat exchanger to take the heat away.

"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..

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.

FF said:

"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..

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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.

"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 .

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!!

makobuilders said:

Sure. But exposed protruding pipes?

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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.

FF said:

"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..

Click to expand...

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.

sunchaser said:

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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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.

Delfin said:

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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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.

Delfin said:

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.

Click to expand...

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.

twistedtree said:

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.

Click to expand...

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.