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Old 04-11-2010, 08:02 PM   #21
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RE: wet vs dry exhaust

Many good points made here.* It is true that some engines will have more of a soot problem with a dry stack than others.* The CAT 3208 is notorious for belching black, as are many Detroits.* I have a 3306, and there is no soot.* I get more from the Kabola than I do from the CAT.*

Gensets can be a nuisance with a dry stack, but the question was not about gensets.* Mine is keel cooled with a wet exhaust through a gas/water separator for all the reasons stated.

I assumed keel cooling in my answer, but I suppose if you wanted the worst of both worlds you could go dry stack with wet cooling.* If you go dry, go keel cooled, closed system, coolant only.* Delfin was blessed with half pipe welded on the hull, which we used for hydraulic cooling on one side and a/c cooling on the other.* We added Walter keel coolers for the CAT and genset.

My impression is that commercials go dry because it is the simplest and cheapest system to use, maintain and they couldn't give a rip about soot on their, or some dude boat tied up next to them.* Having tied up next to a few, this I can attest to.

There is no difference between the heat of an ER with wet or dry exhaust, since the source of the heat is the engine, not the exhaust, and cooling the exhaust after it leaves the hot engine is going to have a minimal impact on ER temperature, especially if the dry stack is insulated, which it always is.
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Old 04-12-2010, 08:39 AM   #22
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RE: wet vs dry exhaust

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Delfin wrote:

There is no difference between the heat of an ER with wet or dry exhaust, since the source of the heat is the engine, not the exhaust, and cooling the exhaust after it leaves the hot engine is going to have a minimal impact on ER temperature, especially if the dry stack is insulated, which it always is.
That is almost as good as the one about mouse milk.

Using a little Cat 3054 as an example, to produce 108 hp it converts 6.2 gph of diesel per hour to about 13, 435 BTUs per minute.

Of those 13,435 BTUs, 4660 turn the prop. About 4200 leave the boat via the cooling system, and 3250 go out the exhaust stack. About 1325 radiate into the engine room from the engine.

If you don't believe the heat leaving via the exhaust is minimal, turn off the water to the spray ring of a wet exhaust system and let us know how it turns out.

I was on a boat last week after the crew ran the main engine for a few minutes with no water to the spray ring and the area around the wet exhaust pipe became hot enough to soften a 10 foot length of 1.5 inch CPVC vacuum piping to the point of collapse.
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Old 04-12-2010, 04:28 PM   #23
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RE: wet vs dry exhaust

Since I can put my hand on the exhaust stack wrapping 6 inches from the turbo, once of two things are true.* It is not hot, ergo, not radiating heat into the E/R, or the mouse milk I have been drinking has bestowed super human characteristics.* Yes, there is heat going up the insulated stack. Yes, there is heat exiting via the wet exhaust.* With neither dry nor wet exhaust is the heat going into the E/R.


As usual, Rick, you must be right even when you are wrong.
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Old 04-12-2010, 05:19 PM   #24
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RE: wet vs dry exhaust

Delfin - How far up your pipe/stack, after exiting engine, *does your vessel*have insulation (the grey stuff ??) wrap*before the transition to*a "pipe in a pipe" setup. Some yacht stacks are designed to pull "cool" air up the stack enclosure to keep temps down. Does yours do this? Most Cat EGTs exceed 600 deg at cruise* - do you recall yours?
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Old 04-12-2010, 06:03 PM   #25
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RE: wet vs dry exhaust

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Delfin wrote:

Since I can put my hand on the exhaust stack wrapping 6 inches from the turbo, once of two things are true.
Yeah, one of which is your exhaust pipe is well insulated. No telling what you might say next after reading your last contribution.

What can I say? You are the one who wrote: "cooling the exhaust after it leaves the hot engine is going to have a minimal impact on ER temperature ..."* If you want to believe the earth is flat that is your business, but don't expect some of us to laugh at your ignorance when you post such a statement.

Ask one of the readers here to divert the water flow from their wet exhaust spray ring and let us know how hot it gets in the engine room.



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Old 04-12-2010, 06:10 PM   #26
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RE: wet vs dry exhaust

TG, as the pipe exits the turbo, we have a flex 90 with wrapping around it, then a wrapped straight run up through an insulated raceway to the 'stack house' where the muffler is.* The raceway has the surplus air blown into the ER for combustion running up the stack, where it exits through vents in the stack house.* In the ER photos in this link, you can see the arrangement:
<a href="http://delfin.talkspot.com/aspx/blob2/blobpage.aspx/msgid/555531">
http://delfin.talkspot.com/aspx/blob2/blobpage.aspx/msgid/555531</a>

With this setup, there is no heat from the stack added to the ER beyond what the block itself radiates.* Wet exhaust would not make it any cooler than it already is.

I run pretty slow most of the time - around 1200 rpm, burning about 3.25 gph at 7.5 - 8 knots, with the EGT at about 550 degrees.* Cylinder temperatures are about 570 degrees, regardless of the RPMs, at least according to the heat gun.* Every 20 hours or whenever I remember, running up to 1650 rpm will heat it up the EGT to around 675 degrees.* I'll get about a minute of blacker smoke, which then clears to invisible after that.
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Old 05-02-2010, 05:16 PM   #27
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RE: wet vs dry exhaust

I wouldn't do it on any vessel smaller than 50-ft, as most weren't designed for it.* We have it on our gulet and so far the engine has lasted much longer than the previous vessel with a wet intake/exhaust.* Our engine is small - 3.9L Cummins, which turns a respectable 950 continuous rpms, but with the keel cooler installed at the shipyard and the internal coolant system, I don't expect to replace the engine before the vessel - maybe in ten more years.

I have seen several commercial boats here in Panama undergoing re-fits to change out the wet for dry.* It's far more efficient and less costly in the long run.
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Old 05-02-2010, 09:34 PM   #28
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wet vs dry exhaust

Reefhunter, since you have experience with wet as well as dry exhaust, do you have an opinion on any of the following on your Gulet:

1.* It would be cooler in the E/R with a wet exhaust,
2.* It's noisier in the boat with the dry exhaust than it would be with a wet system,
3.* You would spend less time cleaning soot with a wet exhaust than you do now with the dry,
4.* You spend more time maintaining the cooling system on your dry exhaust than you would with a wet.

Thanks!

-- Edited by Delfin on Sunday 2nd of May 2010 09:38:09 PM
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Old 05-03-2010, 04:32 AM   #29
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RE: wet vs dry exhaust

" It would be cooler in the E/R with a wet exhaust,"

Weather the exhaust manifold is wet is a simple decision of what is Off The Shelf.

Installing a truck engine the sales volume is low for a mfg to create a wet exhaust manifold .

Weather the manifold dumps into the wet exhaust , or is part of the engines cooling system , only increases the cooling requirements of the keel cooler by a couple of bucks.

Either way , the wet exhaust manifold will still be 180F or so , so an insulating wrap would help the engine room temperature , as well as a damn good powered ER blower setup.
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Old 05-03-2010, 08:51 AM   #30
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RE: wet vs dry exhaust

FF

For wet exhasut setups, no blower should be needed when running unless design is off kilter or ER intakes marginal. Of course in the cooler climes,* ER temperature is normally a non-issue. The heat protection wraps are as much for safety as for lowering temperatures. On my vessel, there is about 8"-12" of wrap between engine exhaust and main exhaust tube leading to the water lift. Hardly a big deal.

The exhaust design in*dry cases is the key for ER temperature control.
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Old 05-03-2010, 09:07 AM   #31
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RE: wet vs dry exhaust

FF, I was only asking Reefhunter's opinion on E/R temps with wet vs. dry, not assuming a wet exhaust system would create a cooler E/R.* In fact, in all physical world's other than RickB's special universe, the laws of thermodynamics determine how hot the E/R will be for a given set of conditions.* In fairness to RickB, if you sabotage the wet exhaust, the heat that would have been transferred out will in part be radiated in and the E/R temps will rise.* But in a* system not designed by an idiot or subject to sabotage by Rick, since the only propulsion source of heat is the engine itself, the exhaust system is immaterial to how hot the engine room gets.
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Old 05-03-2010, 09:28 AM   #32
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RE: wet vs dry exhaust

Where I live and boat Heat is a good thing. I have to dodge ice most of the year. I have a dry stack the stack runs right up thru the head. Makes it nice and toastie when nature calls.

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Old 05-03-2010, 12:07 PM   #33
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RE: wet vs dry exhaust

"... since the only propulsion source of heat is the engine itself, the exhaust system is immaterial to how hot the engine room gets."


I think you'd better check for an exhaust leak on your boat.
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Old 05-03-2010, 12:22 PM   #34
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RE: wet vs dry exhaust

When we bought the Eagle it was dry exhaust and very loud and hot.* We converted to wet exhaust and heat wrapped from the engine manifold to the raw water connection.* The wet made the engine room, and salon cooler and quieter.*


*
The important thing is the engine manifold is not raw water cooled, not what comes out of the tail pipe.
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Old 05-03-2010, 12:29 PM   #35
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wet vs dry exhaust

Quote:
Phil Fill wrote:

*
When we bought the Eagle it was dry exhaust and very loud and hot.We converted to wet exhaust and heat wrapped from the engine manifold to the raw water connection.The wet made the engine room, and salon cooler and quieter.
*


The important thing is the engine manifold is not raw water cooled, not what comes out of the tail pipe.

*
Phil, Could you post some pics of your engine room? So we can see your set up? It sounds like it was an interesting project.

Thanks,
John

*


-- Edited by Gamekeeper on Monday 3rd of May 2010 12:30:28 PM
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Old 05-03-2010, 02:53 PM   #36
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wet vs dry exhaust

Quote:
RickB wrote:

"... since the only propulsion source of heat is the engine itself, the exhaust system is immaterial to how hot the engine room gets."


I think you'd better check for an exhaust leak on your boat.
So some questioning assumptions from someone who admits to not knowing much about this topic.

An engine generates heat when it's running because of the internal heat of combustion and that heat's distribution thorughout the engine block from being transmitted via the metal, coolant cirulation, etc.* Right, wrong?

The temperature of the exhaust at a given power*setting and load*leaving the cylinders is going to be "x" regardless of what that exhaust gets fed into.* Right, wrong?

The exhaust manifold is going to radiate heat into the engine room.* Right, wrong?

If the exhaust manifold is water cooled, it will radiate less heat into the engine room than a similar but uncooled manifold.* Right, wrong?

If you have a non-water-cooled exhaust manifold and a non-water-cooled muffler and exhaust pipe, those components will radiate heat more heat into the engine room than the same components that are water-cooled.* Right, wrong?

The variable in the previous statement is the insulation on the dry*exhaust manifold, muffler, and exhaust hose/pipe runs.* Right, wrong?

If my assumptions are correct, logic would dictate there are two heat sources in the engine room, not just one.* The engine itself-- a big block of hot metal--- and the exhaust components.* So the type and construction of the exhaust system would seem to have a major effect on heat being radiated from the components.

All of which would lead me to believe that the exhaust system has a definite influence on the amount of*heat in the engine room.



*


-- Edited by Marin on Monday 3rd of May 2010 02:59:32 PM
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Old 05-03-2010, 07:54 PM   #37
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RE: wet vs dry exhaust

Marin, all marine diesels I have seen lately have water cooled exhaust manifolds, whether they have wet or dry exhaust.* Open the hood of your Oldsmobile after a few miles and put our hand on its exhaust manifold and you'll understand why.* My CAT is cooled with coolant, yours might be cooled with sea water.* If sea water, you get the extra fun of hot salt water in your engine, zincs, lowered efficiency, etc., which is one of the reasons commercials usually go dry.* If by manifold you meant the pipe aft of the manifold(s) and turbo (if any), then that is either cooled with water with a wet muffled exhaust, or insulated if a dry.* Either way, there isn't a material difference in heat radiation between the two.* As you note, the source of heat is the engine, not the exhaust pipe.
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Old 05-03-2010, 09:36 PM   #38
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RE: wet vs dry exhaust

The exhaust manifold on an FL120 is cooled with the engine coolant. I did not realize that the exhaust manifolds on dry-stack engines are always liquid-cooled, too. Also, while I know there is insualtion around the dry pipes and mufflers of a dry exhaust I assumed that was just so people wouldn't get burned on them, not to reduce the heat in the engine room. Thanks for the correction.
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Old 05-03-2010, 09:56 PM   #39
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RE: wet vs dry exhaust

Marin, I don't know if all marine diesels have cooled manifolds - I just haven't seen any that aren't because the temperatures would get pretty toasty, as in glow in the dark, 3rd degree burn light your boat on fire toasty just like an automotive engine.* The wrap on a dry stack does keep you from getting burned, but it also serves to nearly eliminate E/R radiant heating.
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Old 05-04-2010, 04:15 AM   #40
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RE: wet vs dry exhaust

"I just haven't seen any that aren't because the temperatures would get pretty toasty, as in glow in the dark, 3rd degree burn light your boat on fire toasty just like an automotive engine. '

Sorry but the exhaust temps of a gas engine are way (400-500F) above a good working diesel.

Most diesels will run 700 deg F or so , a far far distance from glowing in the dark.
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