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Old 04-08-2010, 10:11 AM   #1
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wet vs dry exhaust

wondering what your thoughts are on this subject? has anyone here converted there wet exhaust to dry? where i live its a mud based river with nasty brown water and it cant be good to pump that through my cooling system. in the next year or so I have to replace my wet exhaust hose, total of about 30 ft for both engines and I was considering converting to dry exhaust. on my albin 43*I would run it up where the mast is now and combine both engines into one stack. let me know what you all think, its far on the to do list but its kicking around in the back of my mind.
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Old 04-08-2010, 10:45 AM   #2
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RE: wet vs dry exhaust

This is really not practical for a small vessel. First, your engine was not designed for this and secondly you will be introducing a great deal of extra noise and heat that you boat was not built for. Without all of the details, I believe you will be extremely unhappy with the results and invest a lot of money into something you won't want nor will anyone else should you ever chose to sell the boat. The only issue that is created by silt in your coolant water is impellers, and you can replace a lot of impellers for the cost of a dry exhaust. Chuck
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Old 04-08-2010, 11:56 AM   #3
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wet vs dry exhaust

Quote:
albin43 wrote:

where i live its a mud based river with nasty brown water and it cant be good to pump that through my cooling system.
The exhaust is the last waypoint on the trip through the raw water system so any silt has already done its dirty work by the time it reaches the spray ring. You are stuck with pumping the stuff through your heat exchangers anyway so letting it cool and silence the exhaust on the way out is*unlikely to cause further*problems.

Use your creative talents to install a flushing connection for use at the end of each trip if you are worried about filling the system with silt.


-- Edited by RickB on Thursday 8th of April 2010 11:57:25 AM
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Old 04-08-2010, 12:06 PM   #4
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RE: wet vs dry exhaust

While I have no experience with a conversion I would not suggest it be taken on with out the builders support and here are my reasons:
1 EGT's are very high and proper insulation for the stack is critical
2 Structural modifications to the boat are very significant*
3 The effect on the egnine is unknown

Suggest you leave as is or buy a boat designed for Dry Stack.

We apprciate the benefits of dry stack on our two Nordhavn's and would not go back to wet exhaust unless it was a smaller boat.* I think a 40" is the smallest size boat that can accept dry exhuast wihout loosing to much interior space.**
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Old 04-08-2010, 12:43 PM   #5
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RE: wet vs dry exhaust

Even on high end vessels, the best designed dry stack can result in excess heat. Nordhavn has been working on this issue for many*years as some owner's experienced ( in the tropics in particular) high ER temps affecting electronics. To the point some Nordhavns are built to wet exhaust owner criteria to cool down the ER. And dry stack C particles*can make a real mess on the boat is not properly designed.
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Old 04-08-2010, 10:46 PM   #6
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RE: wet vs dry exhaust

The previous owner and builder of my boat installed a dry stack exhaust when he built the boat. When I purchased the boat I found the old exhaust trunk and asked him why he had changed to a wet system. He said he had the following issues with the system.
1. noise while on the fly bridge
2. smell when running down wind.
3. soot on the decks
4. excessive heat in the salon in the summer ( yes it does get warm in the North West )

I still sometimes think about switching back, but the wet system that is currently in the boat works great.... if it isn't broke why change it
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Old 04-09-2010, 03:04 AM   #7
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RE: wet vs dry exhaust

First, your engine was not designed for this and secondly you will be introducing a great deal of extra noise and heat that you boat was not built for."

Most boat motors are transplants (marinizations) of tractor , generator or truck engines.

ALL are created for a dry exhaust and work excellent with the lower back pressure of a dry exhaust. There are few "Marine" engines that were specifically created just to push a boat , at least down in the tiny under 500 shaft HP size.

We have a dry exhaust and keel cooling on out current boat and would never consider a wet exhaust again.

The advantage in winterization or winter operation hassle free would be enough , but as noted silty or sandy water may require the replacement of the sea water impeller in as little as 200 hours , as well as frequent cleaning of the strainer setup.

The exhaust can be as quiet as your wallet is deep.

Cheapo truck muffler with resonator will keep the noise down , but a trip to the generator muffler folks , and a "Hospital Critical" muffler will silence most all the noise.Check Cowl mfg.

Building an insulated exhaust box is not a big deal as the temperature of the stack are modest (at least compaered to gasoline).The low temperatures make the box insulation inexpensive. The exhaust manifold can simply be wrapped to not over heat the engine space..

An added advantage is the exhaust box can be used either as a heat source , or at least to dry the wet gear locker.

Dave Gerr has a fine new book on mechanicals in a boat and covers the wet vs dry setups well.


For Po Boy cruisers the keel cooling + dry exhaust opens a world of excellent engine choices for transplant.

All truck engines have a SAE bellhousing , so a rebuilt Twin Disc , a flex plate and a set of rubber mounts and some new plumbing could make a re power 1/10 of what thew "marine" clowns want.


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Old 04-09-2010, 04:17 AM   #8
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wet vs dry exhaust

Dry vs wet - the question is not can it be done,*the question is why do it? When was the last time you saw a sail boat (not even the Nordhavn MS56) with dry stack? The current champ for explaining small YACHT (not dredges, not shrimpers, not mega yachts, not muddy river users etc)* blue water design using new systems, fresh paper thinking followed by actual construction is Steve Dashew. He is all wet. And his boats are designed for a full capsize. I can think of no logical reason why anyone with an existing *well designed wet system would go to the trouble to do a dry stack. And the topside*mess as the engine matures - fuggadaboutit.

-- Edited by sunchaser on Friday 9th of April 2010 04:28:24 AM
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Old 04-09-2010, 05:43 AM   #9
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wet vs dry exhaust

the "builder" would never support any major change. too much liability.
also the ford lehman is a tractor engine, dry stack would be if anything, better for it.
and to say dry stacks arnt installed in boats this small (43ft) is terriably wrong aswell. look at 80% of the lobster boats and other fishing vessels in the northeast. operation in cold weather such as winters in lake ontario would be much safer with a dry stack. as FF noted you could make it as quiet as you want. my father lives aboard a 46ft tug with a dry stack inclosed in steel and it isnt any louder then my wet. it would cost alot more then replacing hoses for my wet system. I would run both exhaust into one and replace the wood mast with a steel pipe which would serve as the mast/exhaust.

n4061, as stated before the dry exhaust would be anything but worse for the engine. Structural modifications to the boat would be nothing more then cutting a 5 inch hole in the aft trunk, nothing "significant". and tosay 40' is the smallest boat you can have a dry stack and not loose space is crazy. maybe in a nordhavn but it all depends on the design. maybe it isnt best for my application but theres no size limit to a dry stack, more of a design feature.

broken impellers can cause other problems aswell. wintering in the water here in upstate NY with our temps is not good for water in the cooling system if my heat failed while I was at work.* in my opinion dry stack for my application of using the vessel would be better then wet, but maybe not for my albin. not sure yet. as I said this is low on my list.


-- Edited by albin43 on Friday 9th of April 2010 05:58:02 AM
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Old 04-09-2010, 12:12 PM   #10
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RE: wet vs dry exhaust

Dry stack or not, you still have to cool the engine. This means either a raw water/heat exchanger system like you have now or a keel cooler. If you use a raw water system you still have a raw water pump, impeller, hoses, and heat exchanger. The only difference is that the raw water is simply dumped overboard rather than sent out with the exhaust.

While the base engine for the FL120 was designed for trucks and later was used in industrial and agricultural equipment, these all had radiators and a cooling airflow over the radiator. In a boat, replacing the Lehman water jacket exhaust manifold with a "dry" manifold would result in an extremely hot engine room. Of course one could retain the water jacket manifold, cool it with the raw water system, and send the exhaust up a dry stack and the cooling water from the heat exchanger overboard.

All the lobsterboats we saw in Maine and on Prince Edward Island last spring had wet exhausts. We saw hundreds of boats during our trip and I do not recall seeing a single one with a dry exhaust.* Perhaps in other regions lobsterboats use dry exhausts.* All the purse seiners I've seen out here use dry exhausts.** Most of the salmon*trollers do too.
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Old 04-09-2010, 10:24 PM   #11
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RE: wet vs dry exhaust

Dry exhaust is always more compatible with diesel engines than wet exhaust, because that is what they were all designed for.* On a properly sized dry exhaust back pressure is zero.* This is not possible with wet exhaust since the exhaust is doing work rather than flowing through a pipe.* There is a reason why you rarely (never) see a commercial fishing boat over 40' (in the NW at least) with a wet exhaust - commercials go with what is cheapest and best.* Dry stack qualifies.* In my experience, running a CAT 3306 at 1250 rpm with brief episodes at 1800 rpm to blow carbon, soot is a non existent problem.

The point made on increased heat also makes little sense to me.* I suppose the insulated 2' of pipe in my engine room radiates more heat that 12" leading into a wet muffler, but how much compared to the source of the heat - the engine?

We have a 12" x 12" aluminum raceway running from the ER to the stack house.* It is insulated, and the wood framing is set off by 3" of further insulation.* This would be the major drawback on a smaller vessel, but is a non-issue on Delfin because we built around it.* This is why production boats rarely use dry stack - they don't like the raceway, and, while I run at 62 db in the pilot house with the dry stack 60" away, I suppose it would be quieter if the exhaust were 20' away, so I guess that would be another reason production doen't use it.* That said, how many production boats are much quieter than 62 db with wet exhaust?

Dashew likes low and sleek.* Dry stack requires high and away.* Is that possibly one reason why he builds wet?

I'm not sure whether dry stack would work on your vessel or not, but I don't think it is controversial to say that it is a simple fail-safe way of dealing with a necessary evil.*

Having had wet and dry exhaust, dealt with the impeller failure, piping, corrosion and transom soot of wet exhaust, I understand why commercials vessels don't bother with it.
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Old 04-10-2010, 12:48 AM   #12
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RE: wet vs dry exhaust

Quote:
Delfin wrote:Having had wet and dry exhaust, dealt with the impeller failure, piping, corrosion and transom soot of wet exhaust, I understand why commercials vessels don't bother with it.
Unless you have keel cooling, you're going to be dealing with potential impeller failure, pipiing, and corrosion whether you have a dry stack or not.
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Old 04-10-2010, 03:37 AM   #13
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RE: wet vs dry exhaust

"Unless you have keel cooling, you're going to be dealing with potential impeller failure,"

Indeed, but the cost of a keel cooling setup is about the same as a wet entire system.

Unless you do as our Maine boat does 2 -21 ft long 1 1/2 pipe and a couple of nipples and elbows.

The difference is the lack of REQUIRED maint.as the stock engine water p;ump is usually very reliable.

The same can not be claimed for the pile of parts and pieces , impeller kits , tube brushes and filter gaskets required for the less reliable wet setup.
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Old 04-10-2010, 04:31 AM   #14
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RE: wet vs dry exhaust

Delfin --Dashew's*design comes from considering noise (note that PMM found Dashew's Windhorse to have 57dba in cabin), heat (a huge issue in warmer climates with today's electronic engine and system controls), cost, topside soot (not good on Al)*and immersion safety. And of course he is used to designing wet since that is the design he has used for 35 years on all his vessels.

No doubt*for your vessel and others of similar cool water North Sea or PNW clean paper design, dry is "perfect." But then the door and debate opens on what kind of dry design both below and above the waterline. There is as much debate on this issue as there is wet vs dry. Such as type and design of keel coolers, heat dissipation, internal exhaust pipe noise, soot control and manifold, gear and turbo*cooling. And I could never figure out why one would intentionally design*a keel*cooling system subject to breach when boat is even softly grounded.

The question though was converting a smaller trawler from wet to dry. And - broken impellers - never had one in decades of boating, mind you I change mine out frequently and don't wait for failure. I assume you maintain your circulating pumps likewise? And how about a genset or two -*dry stack in a crowded anchorage at night with no muffler - that is not neighborly. My wet Westerbeke genset is SILENT inside and out.**Soot, what is that on a well maintained vessel? But if your engnie is old and tired, rather soot on transom than topsides if one's engine is a spewer.*I note you do not have a big enclosed flybridge. I love mine with no engine noise, no exhaust smell, just solitude underway, clean Strataglas windows and no soot to wipe off the dinghy.
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Old 04-10-2010, 09:41 AM   #15
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RE: wet vs dry exhaust

Years ago we had a neighbor that had a 1960's 55' trawler with dry stack exhaust, He was a commercial pilot and kept the boat and systems in very good condition. It had the same big naturally aspirated john deere that we have in our boat. We at that time had a GB36 that sat directly down wind in the prevailing wind. I used to get so pissed at the guy... and he was a good friend when he would start the boat and run it in gear in the slip. We would get the nastiest soot spotting on the decks and the flybridge windows and sunbrella. I he finally realized the error of his ways and I found him washing my GB one day when I came down to the boat. He never did figure a way to get rid of the soot... but he would start the boat with a pair of panty hose wrapped over the stack and that pretty much cured the issue!

As mentioned previously my boat did have a dry stack previously and the previous owner/builder changed it to wet. He made the comment that one of the reason commercial boats go dry it that the loading of commercial boats often puts the exhaust outlet under water and causes excessive back pressure problems, not typically an issue on rec. boats. I also recall a couple of commercial boat guys that died a few years back when that very thing happened... but it may have been a gas motored boat that caused the asphyxiation, I'm not sure.

In regard to picking up sand and debris.... isn't that what a properly sized sea strainer is for??
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Old 04-11-2010, 05:52 AM   #16
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RE: wet vs dry exhaust

he would start the boat and run it in gear in the slip. We would get the nastiest soot spotting on the decks and the flybridge windows and sunbrella


Chronic underloadinf does cause incomplete combustion.

In gear in the slip this gent was washing out the pilings. deepening his slip but creating a shallow behind the wash and reducing the service life of his engine .

Nice guy!
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Old 04-11-2010, 09:24 AM   #17
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RE: wet vs dry exhaust

Every dry stack boat I know well (3 of them) has a soot on neighbours problem. One went to the pantyhose filters on the stacks for a while, but mostly they watch the wind direction and check on the neighbours after sstarting. One had a couple of Scotch deliveries when tied up close to a particularly cranky neighbour.
None of these does the underloaded running in the slip described above. All run under a good load most of the time, so it's just "soot happens". All are older boats.
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Old 04-11-2010, 06:33 PM   #18
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RE: wet vs dry exhaust

Is there any reason one could not run the dry ehhaust out the side of the hull? If you used a pipe within a pipe and ran a blower trough the outer pipe and insulated the outer, would the airflow dissapate enough heat? This would avoid a stack through the cabin. Point the exhaust tip of the pipe toward the water and the likelyhood of soot on the neighbors boat is greatly reduced. The blower could run for X number of minutes after shut down. I am sure someone has thought of this. What am I missing?

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Old 04-11-2010, 07:34 PM   #19
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RE: wet vs dry exhaust

US Coast Guard does it. Just have to design it properly.
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Old 04-11-2010, 07:59 PM   #20
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RE: wet vs dry exhaust

Quote:
FF wrote:

"Chronic under loading does cause incomplete combustion.
In gear in the slip this gent was washing out the pilings. deepening his slip but creating a shallow behind the wash and reducing the service life of his engine Nice guy!"

The aforementioned neighbor did as I believe we all do a few times each winter... He ran the boat for about 10 minutes, basically at idle.. in gear in his slip. No issue with the concrete pilings, except knocks the crap off of them, and the depth in our area of the marina is around 25' deep with a grassy bottom.* In the northwest we don't haul boats for the winter, and the area is rather windy in winter so it is not at all uncommon to do this if you are short handed when visiting the boat. I try to take the boat out and run it HARD every 3rd time I do this for about 15/20 minutes to lessen carbon/soot buildup.

The point is that wet or dry both have pluses and minuses... the math is up to each individual.... but I will say I have never had my boat sooted up by a neighbor with a wet exhaust!*

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