heat exchanger vs std cooling

[captain ray]

Does anyone have information regarding the pros and cons of keel coolers vs standard cooling methods?--Thanks, Captain ray

[gjordan]

Ray, if you give the type ,size,construction(wood,glass,metal?) and intended use of the boat, it will make it easier to come up with answers(opinions). There is nothing wrong with keel cooling, but remember that you still need a through hull and salt water pump to cool the exhaust, unless you go with a DRY STACK which tends to be much noisier. Good Luck ______Grant.

[djmarchand]

Keel cooling almost always includes a dry stack exhaust. If you have to install a sea water pump to cool the exhaust, why not cool the engine with the same water.

Keel coolers certainly are reliable. The glycol engine circulating pump (the one that pumps the glycol to and from the keel cooler is much, much more reliable than a water pump">raw water pump. And you may have a use for the sea water drive like a hydraulic pump or whatever.

But dry stack exhausts are bulky, require insulation and a chimney/chase to carry the heat up and out. Soot from the exhaust often falls on the boat. So they are rarely used in recreational boats.

David

[skipmac]

The dry stack is definitely the downside to using a keel cooler. I was all for it until someone pointed out that little detail. Had not thought of keeping a salt water pump just to cool the exhaust. That is an idea.

The other concern with a keel cooler is corrosion and potential damage to the system from bumping into debris or whatever.

[stillbuilding]

Originally Posted by captain ray

Does anyone have information regarding the pros and cons of keel coolers vs standard cooling methods?--Thanks, Captain ray

I chose to keel cool to avoid the issues that go with failed salt water impellers, the risk of engine overheating due to blocked intake. I still have salt water for exhaust cooling so is not a complete solution but exhaust heating probably slower onset and more time to intervene. Keel cooling probably better in heavily silted, shallow areas or with lots of plastic. Arguably eliminates the issues of engine flooding with prolonged starting problems - minor virtue. One less intake to fail.

[stillbuilding]

Originally Posted by skipmac

The other concern with a keel cooler is corrosion and potential damage to the system from bumping into debris or whatever.

On a steel boat the cooling runs are welded on channel and not easily damaged. Appropriate fairing probably reduces risk in other hull materials.

[goboatingnow]

I know of several keel cooler installations where the engine can not be used off any length of time under any load, if the boat is not moving through the water !

dave

[stillbuilding]

Originally Posted by goboatingnow

I know of several keel cooler installations where the engine can not be used off any length of time under any load, if the boat is not moving through the water ! dave

Inadequately designed/built obviously. There is good design data available that i have found in texts previously. I did the calcs then doubled it - no problem in steel.

[lituya1617]

Advantages of keel coolers: very reliable, they isolate engines from (salt) water vapors in the exhaust circuit (dry stack) which often destroy engines, no moving parts, no pumping of large volumes of water into the boat (many sinkings attributed to this), coolant pump is original engine-mounted centrifugal pump which is very reliable, low cost, easily fabricated by a good diy person, less parasitic power loss than wet exhaust/in-hull heat exchanger, fewer hose connections and parts. Advantages of wet exhaust systems: standard design and easily understood. About dry exhaust systems: small diesel engines have small exhausts and the needed insulation around the exhaust takes up less room than a 4-inch pipe. The exhaust stack is hardly intrusive among the many pipes and lines around the cockpit of a normal recreational boat. Muffling is easy and highly effective with a standard (cheap) automotive muffler. If the engine is properly tuned, it will not spit out soot. With a tall (80 inch high) stack, there will be no odor even when the air is calm. A dry exhaust costs a tenth of a wet exhaust because automotive/truck parts can be used. Steam pipe insulation and wrap below decks prevents burns while above deck the exhaust is kept inside an outer pipe that passively vents engine room air by convection. This is the system used on almost all smaller commercial fishing boats, for very good reasons.

[mvweebles]

Pretty good article from Steve d'Antonio. In summary, both are good and both can be well designed and trouble-free. He likens it to anchor selection.

https://www.proboat.com/2017/11/clea...e-dry-exhaust/

Nordhavn trawler yachts are almost always delivered with dry-stack exhaust. I know a guy having his second one built - this one with wet exhaust. He cites factors of soot and accessibility to maintenance items, meaning you can easily change an impellor from inside the boat, but need a diver to change a zinc for a keel cooler (also cited in the Steve d article above). Both boats were multi-million dollar boats, and I am sure he will take a small price hit when time comes to sell his wet exhaust Nordhavn as they are synonymous with dry stack, but tough to argue with a guy who has owned two and decided second one would be wet.

I also know a guy who had a Willard 40 trawler yacht built. At the time, he was a VP with Willard and specified his engine to be wet exhaust but with a keel cooler instead of the traditional heat exchanger. At the time, seemed like a great idea, but I wonder where one would fetch broken impeller vanes if needed as they always land in the heat exchanger.

Finally, I know of a Chinese builder of George Buehler designed Diesel Duck trawler yachts in steel. Knowing that dry exhaust have marketing appeal with the offshore trawler set (e.g. Nordhavn), they delivered the early ones with dry stack. They had problems with overheating due to inability to evacuate massive amounts of heat given the configuration limitations of running the stack through living quarters. Turns out that most recreational dry stack boats have huge, expensive blowers that are as critical to cooling dry stacks as raw water pumps are to wet exhaust. The Chinese builder quickly turned to wet exhaust and will no longer construct with dry.

In the end, no free lunch. For recreational boats, I'm almost positive a dry stack is much, much more expensive than a wet exhaust. Probably by several multiples.

[Montanan]

Reference: https://www.passagemaker.com/technic...ooler-retrofit

[Montanan]

Reference:

https://www.sbmar.com/walter-marine-keel-coolers/

[Montanan]

Reference: Duramax Heat Exchange Systems: DuraCooler Ship Cooling System

DuraCooler design features help increase heat transfer by more than 17%.
cooler Duramax DuraCooler Patented Streamlined Header Design
Our streamlined entry and exit flow header greatly enhance interior coolant and exterior seawater flow patterns while reducing system pressure drop within the keel cooler unit

Plumbing Options
Single Pass
Nozzles on opposite ends of the cooler to accommodate internal plumbing. Nozzles are available in various lengths and diameters.

Double Pass
For internal plumbing that requires nozzles on the same end of the cooler. Allows the internally to be more centrally located.

Through-Hull Nozzle Design

Nozzle size and diameter manufactured for specific application. Two piece header design allows for braising on inside and outside of the header which, in turn, increases the integrity and reduces the chance of leakage. A Sea chest or cofferdam is required by A.B.S.

Flange-Mount Design
This is for non-through-hull applications. Hardware is located outside the hull for easy access. It is recommended when space inside the hull is tight or equipment makes through-hull inaccessible. No internal cofferdam or sea chest is needed.

[DougR]

Advantages:
- less chance of seawater pump failure overheating the engine
- less chance of mud/debris/ slush ice plugging the sea water side of the cooling system
- less winterizing the cooling system ( if dry exhaust)
- no seawater pump maintenance if dry exhaust

Disadvantages:
- normally heavier than a HE cooled engine
- more antifreeze volume to change
- can be difficult to clean internally
- more underwater drag
- antifouling paint can reduce cooling efficiency, requiring a larger KC, particularly in warm water areas
- may or may not automatically work with the factory supplied circulation pump. All circ pumps are designed to pump adequate coolant with a given external cooling circuit pressure drop. Heat exchangers and radiators normally have very low delta P, because the pipe runs are short, measured in inches. Keel coolers may be five or six feet long with several turns, plus hose length inside the boat. The standard circ pump may not provide enough flow against the increased flow resistance of a KC.
- turbo/aftercooled engines frequently require two keel cooler circuits. One for the engine and one for the after cooler, because the return water temps in the engine KC cannot get low enough for aftercooler efficiency. Many modern engines in the 75h.p. and above size are aftercooled....

[skipperpete]

Originally Posted by Montanan

Reference: Duramax Heat Exchange Systems: DuraCooler Ship Cooling System



DuraCooler design features help increase heat transfer by more than 17%.

cooler Duramax DuraCooler Patented Streamlined Header Design

Our streamlined entry and exit flow header greatly enhance interior coolant and exterior seawater flow patterns while reducing system pressure drop within the keel cooler unit



Plumbing Options

Single Pass

Nozzles on opposite ends of the cooler to accommodate internal plumbing. Nozzles are available in various lengths and diameters.



Double Pass

For internal plumbing that requires nozzles on the same end of the cooler. Allows the internally to be more centrally located.



Through-Hull Nozzle Design



Nozzle size and diameter manufactured for specific application. Two piece header design allows for braising on inside and outside of the header which, in turn, increases the integrity and reduces the chance of leakage. A Sea chest or cofferdam is required by A.B.S.



Flange-Mount Design

This is for non-through-hull applications. Hardware is located outside the hull for easy access. It is recommended when space inside the hull is tight or equipment makes through-hull inaccessible. No internal cofferdam or sea chest is needed.

Beautiful engineering but they must be damned hard to clean and antifoul.