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Old 10-20-2018, 01:00 AM   #1
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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.?
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Old 10-20-2018, 02:17 AM   #2
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Virtually every commercial boat on the planet is keel cooled - it works.
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Old 10-20-2018, 02:26 AM   #3
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Sure. But exposed protruding pipes?
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Old 10-20-2018, 03:21 AM   #4
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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.
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Old 10-20-2018, 05:42 AM   #5
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Sure. But exposed protruding pipes?
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?
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Old 10-20-2018, 06:35 AM   #6
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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.
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Old 10-20-2018, 06:48 AM   #7
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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).

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Old 10-20-2018, 07:21 AM   #8
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OC, I tend to agree with you. Thanks
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Old 10-20-2018, 08:49 AM   #9
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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.
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Old 10-20-2018, 09:09 AM   #10
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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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Old 10-20-2018, 10:35 AM   #11
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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.

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.
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Old 10-20-2018, 10:42 AM   #12
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My entire keel is the cooler.
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Old 10-20-2018, 11:56 AM   #13
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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!!
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Old 10-20-2018, 12:31 PM   #14
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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.
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Old 10-20-2018, 01:08 PM   #15
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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.
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Old 10-20-2018, 01:47 PM   #16
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I don't understand what you mean by "split pipe".
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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Old 10-20-2018, 02:38 PM   #17
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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


Got it, thanks.
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Old 10-21-2018, 07:07 AM   #18
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"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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Old 10-21-2018, 08:32 AM   #19
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"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.

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.
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Old 10-21-2018, 08:51 AM   #20
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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..
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