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Old 05-04-2010, 05:37 AM   #41
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RE: wet vs dry exhaust

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Marin wrote:

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.
Only the smaller industrial and automotive conversions use water cooled manifolds. Larger engines, especially turbo'ed versions use insulated exhaust lines. Heat in the exhaust is too valuable to throw away before it goes to work in the turbo.

The rules call for insulation to reduce the temperature of exposed piping to <180*F for crew safety and to reduce the fire hazard created by things like fuel and hydraulic leaks, and poorly stored items. The radiant heat from an exhaust can be as damaging as an actual fire and will start a real one rapidly.

You will notice that a wet exhaust below the spray ring does not require any special treatment. That is because adding water to the exhaust cools it below the level it can do any damage. If water is lost, the exhaust will burn and it will burn anything around it. This trashes the silly idea that all the heat in an engine room comes from the tiny amount radiated by the block itself. Go back and read the heat balance figures I posted earlier to see where the heat goes.
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Old 05-04-2010, 05:39 AM   #42
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RE: wet vs dry exhaust

Ridlyme and proper design pretty well deal with any issues arising from seawater cooling of the exhaust manifold. My manifold temps (measured with IR gun) run about 20 degrees F cooler than the engine. Measuring these temps and others around an engine room are great for detecting a variety of early warning signs. As an aside, I am routinely comparing seawater inlet temps to PSS shaft log temps. There should be no more than a few degrees difference.

I*lament the fact that that my seawater cooled manifolds will outlive my remaining boating years. Is gin a good human consumption substitute for Ridlyme?? Hmmmm.
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Old 05-04-2010, 07:25 AM   #43
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RE: wet vs dry exhaust

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RickB wrote:Only the smaller industrial and automotive conversions use water cooled manifolds.
John Deere describes their entire marine line in the Features and Benefits section of their data sheets as having Water Cooled Manifolds.* CAT indicates that most all of their engines this side of 1,500 hp as having either air shielded, water cooled exhaust manifolds, or like my 3306B as having water cooled manifolds.* The same can be said of Volvo, etc., etc.*

I'm not sure what your comment means, but it doesn't seem to map to the way marine diesels are manufactured and sold.



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Old 05-04-2010, 07:30 AM   #44
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RE: wet vs dry exhaust

Sunchaser, your post actually highlights one of the engineering concerns of any cooled manifold, whether sea water or coolant, which is that it actually isn't optimum for engine efficiency for the exhaust to be anything other than blistering hot. I assume that's why no one cools the exhaust when safety can be maintained without the cooling.
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Old 05-04-2010, 07:48 AM   #45
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RE: wet vs dry exhaust

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Delfin wrote:I'm not sure what your comment means ...
********* Obviously.
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Old 05-04-2010, 07:56 AM   #46
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RE: wet vs dry exhaust

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Delfin wrote:... *it actually isn't optimum for engine efficiency for the exhaust to be anything other than blistering hot.
A "blistering hot" exhaust is a sign of inefficiency. The most efficient engine will have the coolest exhaust.

There is nothing to be gained by conserving any heat beyond the turbocharger or heat recovery devices other than that required to prevent condensation of moisture in the exhaust stack of a dry stack system.
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Old 05-04-2010, 08:08 AM   #47
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RE: wet vs dry exhaust

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RickB wrote:Delfin wrote:I'm not sure what your comment means ...
Obviously.Actually Rick, I was attempting to be polite. I did understand what you wrote, so let me be clearer in what I meant.* Your statement that "Only the smaller industrial and automotive conversions use water cooled manifolds" would only be made by a lawnmower mechanic who retired in 1967.* It is contradicted by the manufacturers of these engines.* My suggestion is a subscription to boatdiesel.com.* They have a wonderful section that includes the data sheets on virtually every marine diesel engine made, and you can learn a lot about diesel engines there.*

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Old 05-04-2010, 08:55 AM   #48
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wet vs dry exhaust

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Delfin wrote: Actually Rick, I was attempting to be polite.

Well, it was another failed attempt. Anything under the 1500 hp or so that you mentioned is a marinized design of an industrial engine or it is an automotive or industrial engine produced for the microscopic marine market.

It is painfully obvious that*your knowledge, such as it is, is limited to your trawler and similar boats but those boats*don't reflect the marine industry and marine propulsion in general. They are just the limit of your small universe and the generalizations you understand to be true for your limited experience don't "hold water" everywhere.
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-- Edited by RickB on Tuesday 4th of May 2010 08:55:37 AM

-- Edited by RickB on Tuesday 4th of May 2010 08:59:14 AM
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Old 05-04-2010, 09:07 AM   #49
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RE: wet vs dry exhaust

Quite correct, Rick.* I will try to limit my comments to the small universe of those sites interested in trawlers and the type of marine diesel engines that are used in those trawlers.* You won't find me posting on any sites dedicated to oil tankers, diesel locomotives, gas turbines or pebble bed reactors.* Nosirree.
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Old 05-04-2010, 09:18 AM   #50
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RE: wet vs dry exhaust

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Delfin wrote:You won't find me posting on any sites dedicated to oil tankers, diesel locomotives, gas turbines or pebble bed reactors.*
That is probably a good decision on your part. Since you don't understand the concepts which underpin the operation of the engine in your own boat, you would probably get*laughed*off those other sites pretty quickly.

If you weren't such a twit*you could probably learn something though.

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Old 05-04-2010, 05:50 PM   #51
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RE: wet vs dry exhaust

Aww for crying out loud, would you two call a truce? I think you both have plenty of knowledgeable information to offer, and it seems to me that your arguing about two different classes of engines, and your both correct.* I think we all enjoy a spirited and RESPECTFULL discussion.* It's very possible to discuss, disagree, and still remain civil to each other.* I find both of you to be very knowledgeable, informative and entertaining, but cringe when things degenerate to name calling.** This is not a contest to see who is smarter, it's a free flow of ideas.* Some may hold more water than others, but thats how we all learn.* Feel free to disagree, but do it respectfully.* Keep up the postings though, we all stand to gain as NO ONE knows it all.

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Old 05-04-2010, 05:54 PM   #52
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RE: wet vs dry exhaust

Amen.
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Old 05-04-2010, 08:26 PM   #53
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RE: wet vs dry exhaust

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Arctic Traveller wrote:

It's very possible to discuss, disagree, and still remain civil ...
Marinized forklift engines or 100,000 hp two strokes, the thermodynamics are the same, and the Earth isn't flat. There really isn't much to disagree with. Carnot figured it out, Diesel made it work and anyone who tries to argue otherwise is still a twit.

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Old 05-06-2010, 05:40 PM   #54
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RE: wet vs dry exhaust

Well, whatever - on Penta as originally built (as a commercial fish boat) the exhaust (dry) consisted of a pair of 45 degree elbows from the manifold to the vertical stack which ran up the center of the aft wheelhouse cabin with the muffler above the cabin top. When I converted her I changed this system to the following; from the manifold (water cooled) through a "flex joint" to a short length of 3" steel pipe to a "Mac Muffler", then more 3" pipe to the port aft corner of the extended main cabin, to the vertical via 2 - 45's and up through the cabin top. The vertical run through the cabin is enclosed in sections of domestic stainless steel insulated chimney pipe that has an inner diameter of 8" which leaves a lot of air space around the pipe. From the manifold to the vertical run the system is wrapped in lagging (4 layers) so that the majority of the heat will stay in the pipe.
While I admittedly have not had a chance to run with this new system it has to be better than the old one which incidentally did not radiate all that much heat, sure the stack got hot but never enough to cause concern of a fire starting and the engine room here in the PNW was never that warm that it was uncomfortable to work in there while running.
The chimney pipe I am using is rated for zero clearance to combustibles with an internal gas temperature of 1400 degree F. so there will not be a dangerous heat problem within the cabin.
I have seen this sort of system in many wooden vessels here in this area as well as on the Great Lakes and none of them seem to have had any problems with excessive heat from the system and it sure is a lot simpler, coupled with a keel cooler, than what a "wet" system would be.
Just one goofy Canucks way of doing things !!
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Old 05-06-2010, 07:18 PM   #55
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RE: wet vs dry exhaust

Penta, since you have a water cooled exhaust manifold, yours must be one of those oddball marine engines less than 1,500 hp, like mine.* But even putt putt motors like ours have pretty big mufflers.* Did you wrap yours as well as the pipe and does it get in the way?
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Old 05-06-2010, 09:21 PM   #56
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RE: wet vs dry exhaust

Delfin, et-al

Well for one thing my engine is a completely, specially designed marine engine from back in time when they did things like that. It is a Volvo, Model MD-47 - Series "Starke"
It produces 85 HP at 2500 RPM, natural intake and built in the late '60s and currently has just over 5000 Hrs since a total rebuild.
The exhaust run including the muffler is under the main cabin floor and is entirely wrapped in lagging. I built an insulated "duct" that the system runs through just to keep the air flow confined to the engine room and the exhuast "duct" so that I would have the maximum air flow up the insulated stack.
All this is in what you might call excess space and does not intrude in the engine room.
The way the boat is set up the tanks, fresh water and holding, are mid ships directly aft of the engine room and this exhaust system runs outboard, port side to the tanks, in what would be somewhat unusable storage as it is under the floor below the dinette.
I hope this all make sence to you but if you want I can try taking some pictures of it and send them to you.

John, Penta
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Old 05-07-2010, 04:27 AM   #57
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RE: wet vs dry exhaust

Sounds nicely done, Penta.
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