Wet versus Dry exhaust

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
My boat has a dry exhaust, which I’m perfectly happy with. Older, simpler, all mechanical Lugger engine. I have had no issues with soot since I adjusted the valves just after purchase. I don’t know if that had anything to do with it. Dry stack does give you different things to worry about. I fret about the muffler rusting out, completely concealed on my boat, instead of worrying about wet exhaust elbows. Only real difference that might push me to one system over the other is noise level on the flybridge. How much noise is too much is a very personal thing. It does provide a warm spot on the boat deck where the stack cooling fan vents outside that makes a nice spot to sit on cool days.
 
Delfin said:
And vice versa. Wet exhaust can be closed circuit keel cooled. My genset is wet exhaust and keel cooled because I couldn't figure out a graceful way of providing dry stack exhaust for it.
Click to expand...


This was the point I was about to make. Unfortunately, not all hulls lend themselves to being keel cooled. Also, areas of operation can damage the keel coolers if they aren't protected in some way.
 
Sabre602 said:
The peace of mind from not having hot salt water circulating through the engine room is incalculable.
Click to expand...
If this is so, how do you cool your engine? Every engine requires a water circulation system, raw water or keel coolers (hot salt water circulating through the engine room), regardless of the exhaust system, for engine cooling.
 
Last edited:
foreverunderway said:
If this is so, how do you cool your engine? Every engine requires a water circulation system or keel coolers (hot salt water circulating through the engine room), regardless of the exhaust system, for engine cooling.
Click to expand...

Keel coolers are generally closed systems containing coolant, not salt water. If it wasn't for a wet exhaust muffled genset and water maker, I'd need no through hulls.
 
Delfin said:
Keel coolers are generally closed systems containing coolant, not salt water. If it wasn't for a wet exhaust muffled genset and water maker, I'd need no through hulls.
Click to expand...
Keel coolers require thru-hull fittings and have their own problems. I realize they do not use seawater, but they can get holes in the system and if this goes unnoticed, it can cause corrosion in the engine and lead to engine failure. They also do not function well in warmer waters, so if you have them, you may have a problem if you take your vessel from cool water to the tropics. At any rate, you are still circulating hot liquid around your engine room.
I don't see why you require a wet exhaust for your genset if you don't have one on your ME. I've seen innumerable dry exhaust gensets over the years.
 
foreverunderway said:
Keel coolers require thru-hull fittings and have their own problems. I realize they do not use seawater, but they can get holes in the system and if this goes unnoticed, it can cause corrosion in the engine and lead to engine failure. They also do not function well in warmer waters, so if you have them, you may have a problem if you take your vessel from cool water to the tropics. At any rate, you are still circulating hot liquid around your engine room.
I don't see why you require a wet exhaust for your genset if you don't have one on your ME. I've seen innumerable dry exhaust gensets over the years.
Click to expand...

How would you not notice that the coolant is no longer red or green but now looks remarkably like sea water? And how long would one have to run sea water through the cooling system to have corrosion that matters? My old sea water cooled Sabb didn't seem to mind.

Poorly designed systems don't perform well in all sorts of conditions, but it is incorrect to say that keel cooled systems don't function well in warm waters.

Circulating hot liquids? Well yes, but I thought your objection was to the idea that circulating hot sea water was unavoidable.

Thanks for the engineering tip on my lack of a need for a wet muffler on the genset. Should have had you around when we were designing that installation.
 
Delfin;724322. Thanks for the engineering tip on my lack of a need for a wet muffler on the genset. Should have had you around when we were designing that installation.[/QUOTE said:
It would have been my pleasure.
Click to expand...
 
Delfin said:
Still confused about your position. Do you think that circulating hot sea water is inevitable as you stated in post 34, or circulating hot coolant as you stated in post 36?
Click to expand...
'Raw water' need not be saltwater, but I did mean 'circulating hot coolant' and probably should have been more exact.
However, I do dispute the efficiency of keel cooling designed for northern waters like Frisco to Alaska (I've worked on many a crab and salmon boat) in tropical waters of 80+ degrees.
 
foreverunderway said:
'Raw water' need not be saltwater, but I did mean 'circulating hot coolant' and probably should have been more exact.
However, I do dispute the efficiency of keel cooling designed for northern waters like Frisco to Alaska (I've worked on many a crab and salmon boat) in tropical waters of 80+ degrees.
Click to expand...

Ah, perhaps there is a different use of the word in AK then. In the rest of the known universe, raw water is sea water. It's why it's raw.

With 80 degree tropical water there is a 100 degree delta between the water and the coolant. In the Strait of Rosario, you can add 30 degrees to that, which is not the margin error for a properly sized keel cooler. If your theory were correct, then how on earth do large trucks manage to work in deserts? Or Navy ships keep their engines cool, given the horsepower involved?

The efficiency of a keel cooler is, I believe, determined by 1. raw water temperature, 2. the area and efficiency of the radiating surfaces of the cooler, 3. the velocity of the coolant as determined by the water pump and jacket condition, 4. the heat output of the engine, and 5. the chemical makeup of the coolant. To ensure that the system works, the manufacturers recommendation on sizing uses raw water temperature as a variable, so they work just fine in tropical waters.
 
Delfin said:
Ah, perhaps there is a different use of the word in AK then. In the rest of the known universe, raw water is sea water.
Click to expand...
Ha, ha, ha. I'm guessing you've not operated a vessel on a lake, in which case the 'raw water' engine coolant would most likely be fresh water. Of course, there is always the Great Salt Lake or the Dead Sea, neither place I have operated a vessel upon.
But I can most assuredly state that on the Great Lakes, the vessel I brought from Florida, up the St Lawrence Seaway and back down the Illinois and Mississippi Rivers was using fresh water for its raw water cooling the whole time I was in it.

However, now that this discussion with you has deteriorated into useless babble, I'm gone.
 
Really when you get down to it, keel cooling and heat exchanger (raw water) cooling are the same. Both circulate coolant through a set of tubes that are in contact with sea water, thereby transferring heat from the coolant to the sea water. In one sense, with a keel cooler you take the coolant to the sea water, where with a heat exchanger/raw water system you bring the sea water to the coolant. Both do the cooling job just fine, assuming properly sized. To the extent people prefer one over the other, it's in all the second and third order characteristics and "features" of each approach.
 
twistedtree said:
Really when you get down to it, keel cooling and heat exchanger (raw water) cooling are the same. Both circulate coolant through a set of tubes that are in contact with sea water, thereby transferring heat from the coolant to the sea water.
Click to expand...

That's true. What isn't true is the assertion that keel cooling requires raw water circulating through the boat, which is what the gentleman posted. With a heat exchanger, the raw water is brought on board. With keel cooling, it is not.
 
foreverunderway said:
Ha, ha, ha. I'm guessing you've not operated a vessel on a lake, in which case the 'raw water' engine coolant would most likely be fresh water. Of course, there is always the Great Salt Lake or the Dead Sea, neither place I have operated a vessel upon.
But I can most assuredly state that on the Great Lakes, the vessel I brought from Florida, up the St Lawrence Seaway and back down the Illinois and Mississippi Rivers was using fresh water for its raw water cooling the whole time I was in it.

However, now that this discussion with you has deteriorated into useless babble, I'm gone.
Click to expand...

I see the distinction. In your understanding, raw water, when the boat is in the ocean, means coolant. But if the boat is in fresh water, the raw water is the water the boat floats in. Got it.

Does this mean that your concern about keel cooling not working on the thousands of boats in the tropics using it is restricted to lake boats in the tropics? :angel:
 
foreverunderway said:
Keel coolers require thru-hull fittings and have their own problems. I realize they do not use seawater, but they can get holes in the system and if this goes unnoticed, it can cause corrosion in the engine and lead to engine failure. They also do not function well in warmer waters, so if you have them, you may have a problem if you take your vessel from cool water to the tropics. At any rate, you are still circulating hot liquid around your engine room.
I don't see why you require a wet exhaust for your genset if you don't have one on your ME. I've seen innumerable dry exhaust gensets over the years.
Click to expand...

Keel cooled Nordhavns cruising all over the tropics without issue, not to mention thousands of commercial vessels with KC's. Of course they must be sized correctly to work properly, I occasionally encounter undersized keel coolers, or those with restricted plumbing that run OK at cruise speed, but anything over that causes overheating. KC's are also problematic on gensets, they are prone to overheating if the vessel is stationary unless over-sized, or sized for stationary operation, which makes them prohibitively large in many cases, at least for yachts.

I said earlier there's no wrong answer here, each system, wet and dry, has its own advantages and disadvantages. Boats have burned because of dry exhaust issues, but far more have sunk because of engine raw water plumbing failures.

There is no doubt a dry exhaust vessel needs to be designed around the exhaust, and few designs can properly accommodate such a system. Wet exhausts are far easier to accommodate.
 
I just spoke with a guy about a boat that has dry stack/muffler exhaust but with heat exchanger on engine and no keel cooler.Is there any advantage to this kind of setup? Wouldn’t you still need to cool the water leaving the heat exchanger before it exits the boat? It sounded strange to me.
 
Last edited:
Pack Mule said:
I just spoke with a guy about a boat that has dry stack/muffler exhaust but with heat exchanger on engine and no keel cooler.Is there any advantage to this kind of setup? Wouldn’t you still need to cool the water leaving the heat exchanger before it exits the boat? It sounded strange to me.
Click to expand...

The dragger I used to have up as my avatar had a Deutz 1013 with a dry exhaust and a heat exchanger, the raw water simply went through a hose and overboard through a fitting on the side of the hull, it really doesn't get that hot.
 
Last edited:
I like dry exhaust and a keel cooler for the simple reason that I can use my boat in the winter without draining anything after use. It's also nice to not have a seawater pump to worry about. That being said my current boat has wet because I don't really have much room and the engine came set up that way. I'll change it someday if the need or inspiration arises.
 
Fish53 said:
I like dry exhaust and a keel cooler for the simple reason that I can use my boat in the winter without draining anything after use. It's also nice to not have a seawater pump to worry about. That being said my current boat has wet because I don't really have much room and the engine came set up that way. I'll change it someday if the need or inspiration arises.
Click to expand...

Sounds like kissing your sister to me ..., As in, what's the point?
 
I'm sorry I have to ask, the point about what? I can only assume you've never enjoyed a Maine winter. I'm happy to answer your question.
 
Fish53 said:
I'm sorry I have to ask, the point about what? I can only assume you've never enjoyed a Maine winter. I'm happy to answer your question.
Click to expand...

Sorry about that Mr. Fish - I was responding to PackMule's comment about the boat with dry exhaust and wet cooling, but doing so on my phone sometimes produces erratic results...

And while I haven't had the joy of a full Maine winter, I have spent enough time in NH to feel your pain.
 
Not a problem. To answer your question the boat was that way when I bought it. The heat exchanger is an integral part of the engine, tied in with the oil and turbo cooling. The previous engine had dry exhaust which was thru a trunk from the engine room and I assume they just didn't want to change all that. The system worked fine and as there wasn't really anywhere to run the wet exhaust out with there being a large fish hold behind the engine room there was no reason to change anything.
 
Delfin said:
Sorry about that Mr. Fish - I was responding to PackMule's comment about the boat with dry exhaust and wet cooling, but doing so on my phone sometimes produces erratic results...

And while I haven't had the joy of a full Maine winter, I have spent enough time in NH to feel your pain.
Click to expand...
Maybe the marine engine the builder chose
(100 hp westerbeke ) only came with a heat exchanger but he wanted the dry stack nostalgia or something. I guess there’s no harm but I thought it sounded strange .
 
Steve DAntonio said:
Keel cooled Nordhavns cruising all over the tropics without issue, not to mention thousands of commercial vessels with KC's. Of course they must be sized correctly to work properly, I occasionally encounter undersized keel coolers, or those with restricted plumbing that run OK at cruise speed, but anything over that causes overheating. KC's are also problematic on gensets, they are prone to overheating if the vessel is stationary unless over-sized, or sized for stationary operation, which makes them prohibitively large in many cases, at least for yachts.

I said earlier there's no wrong answer here, each system, wet and dry, has its own advantages and disadvantages. Boats have burned because of dry exhaust issues, but far more have sunk because of engine raw water plumbing failures.

There is no doubt a dry exhaust vessel needs to be designed around the exhaust, and few designs can properly accommodate such a system. Wet exhausts are far easier to accommodate.
Click to expand...

When you spec a keel cooler whether you make your own like we do here in Maine or buy a commercial unit you spec for the highest water temp you normally encounter in your area of operation. There's no problem oversizing as the thermostat will control temp anyway. David Gerr covers various exhaust configurations in his book very well including how to size a keel cooler.
 
Fish53 said:
When you spec a keel cooler whether you make your own like we do here in Maine or buy a commercial unit you spec for the highest water temp you normally encounter in your area of operation. There's no problem oversizing as the thermostat will control temp anyway. David Gerr covers various exhaust configurations in his book very well including how to size a keel cooler.
Click to expand...
Could you give me the title of the specific book you are speaking of? Thanks.
 
It's called "Boat Mechanical Systems Handbook" by Dave Gerr. It's a hardcover book that's very thorough with good illustrations and costs around forty or fifty bucks. His propeller handbook is also very good.
 
Fish53 said:
It's called "Boat Mechanical Systems Handbook" by Dave Gerr. It's a hardcover book that's very thorough with good illustrations and costs around forty or fifty bucks. His propeller handbook is also very good.
Click to expand...
Thank you, sir. I will be on the look out for those next time I'm on Amazon. :thumb:
 
Pack Mule said:
I just spoke with a guy about a boat that has dry stack/muffler exhaust but with heat exchanger on engine and no keel cooler.Is there any advantage to this kind of setup? Wouldn’t you still need to cool the water leaving the heat exchanger before it exits the boat? It sounded strange to me.
Click to expand...



I have that setup. Dry exhaust and the heat exchanger with the raw water going out the hull side. No big deal.
Why would you need to cool the water before it exits the boat. The discharge raw water is NOT hot. It only picks up enough heat to slightly warm it.

The choice was made by the previous owner and I have been living with it, quite happily, for the last 34 years.

Granted the keel cooler is more common but not the only way of doing a good job,.
 
C lectric said:
I have that setup. Dry exhaust and the heat exchanger with the raw water going out the hull side. No big deal.
Why would you need to cool the water before it exits the boat. The discharge raw water is NOT hot. It only picks up enough heat to slightly warm it.

The choice was made by the previous owner and I have been living with it, quite happily, for the last 34 years.

Granted the keel cooler is more common but not the only way of doing a good job,.
Click to expand...
Thanks for the reply. I guess it’s not that strange after all.The boat has a generator and I think it’s set up the same way.
 
Last edited:
You must log in or register to reply here.

Similar threads

O
Wet or Dry Exhaust
Replies
27
Views
3K
Daveo
Daveo
Sababa
Generator Smoke and Soot Under Load
2
Replies
54
Views
4K
Sykes
Sykes
Capt. Dave
New Member - Veteran Owner.
Replies
0
Views
292
Capt. Dave
Capt. Dave
P
Making wet storage area dry on OA Mark 1
Replies
25
Views
3K
DW1979OA
DW1979OA
C
Wet exhaust elbow Northern Lights Lugger 753K
Replies
12
Views
2K
Cigatoo
Cigatoo

Latest posts

Back
Top Bottom