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Old 10-28-2020, 09:19 AM   #21
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My goal is not to convince anyone that Dry Exhaust is bad - it's most definitely not. However, over the years, between Beebe and Nordhavn, dry exhaust is considered sacrosanct - a badge of offshore preparedness for a trawler. Given the nature of the OP's question - can a boat be converted - made me wonder if dry exhaust hype underpinned the OPs question. My 1970 Willard 36 (more or less coincided with Beebe's generation, which is why the W36 is pictured in his original book) originally came with galvanized pipe for exhaust, and was probably straight exhaust at the time - not very reliable. Dry stack made a lot of sense. Since then, wet exhaust has come a long, long way. To their credit, PAE has done an amazing job of designing and fitting dry stack too - not all designers and builders are similarly skilled/committed.

20-years ago, I was influenced by the dry-stack hype and therefore worshipped at the dry-stack alter, but not anymore. I personally would not select a boat based on its exhaust system provided it was properly designed and installed. Wet exhaust is remarkably trouble-free. I'm okay with either. I certainly would not go through any heroic measures to convert from one to the other.

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Old 10-28-2020, 09:54 AM   #22
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Oh well, I'll comment too.
I do have a dry stack but with a heat exchanger. Have had the boat now for 35 yrs. Had to have part of the piping replaced 25 yrs ago at approx $5,000. The actual mufflers are original, 43 yrs. It has been a good system.

However if the boat had a wet system we would have bought it also.
I certainly would NOT change from one system to the other if a boat under consideration already was equipped one way or the other.

If you find a dry stack boat that suits you OR you find a wet exhaust boat that suits you don't let that alone deter you.

As pointed out both will work. What is important is how either design is done AND maintained. If done poorly then then you are going to have trouble. If done well the system should give good service.

But I will say don't let hype, either way, affect you too much.,

And if you really want an exhaust education then go to Seaboard Marine and peruse Tony Athens' articles about exhausts and the MOST important points about weak points .
He has offered huge amounts of info for free

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Old 10-28-2020, 10:14 AM   #23
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Oh well, I'll comment too.

.....However if the boat had a wet system we would have bought it also.
I certainly would NOT change from one system to the other if a boat under consideration already was equipped one way or the other.

If you find a dry stack boat that suits you OR you find a wet exhaust boat that suits you don't let that alone deter you.

As pointed out both will work. What is important is how either design is done AND maintained. If done poorly then then you are going to have trouble. If done well the system should give good service.

But I will say don't let hype, either way, affect you too much.....


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Nicely reasoned.
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Old 10-28-2020, 10:20 AM   #24
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I hope Twisted Tree chimes in. He is having his second Nordhavn built and decided to go with wet exhaust. If you read this blog post from his first Nordhavn, you get a sense of what it takes to cool a dry exhaust.

In short TT went with wet exhaust because both systems need maintenance. Yes, heat exchangers clog up, but so do keel-coolers. Yes, heat exchanges need zincs replaced. But so do keel coolers. Yes, wet exhaust has a water pump, but many dry exhaust installations require an ungodly amount of blowers that are less reliable than engine-mounted gear-driven pumps. He decided he preferred to do maintenance on the inside of the boat instead of outside the boat. Hard to fault his decision.

TT converted me from my prior worship of All Things Beebe and his exaltation of dry-stack exhaust. It deserves a fresh look.

Peter

EDIT - there is a hybrid approach whereby the engine is keel-cooled vs a heat exchanger, but exhaust is raw-water cooled. Depending on your outlook, it's either the best of both worlds or the worst of both worlds. It's a relatively inexpensive conversion if so desired.
I ran a 45 foot crew boat, aluminum hull with keel cooler ( the running strakes were angle welded on the bottom and rigged as a massive keel cooler) and water cooled exhausts. The original engines were Detroits and later changed to John Deers.
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Old 10-28-2020, 10:51 AM   #25
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I own and run one of each.
I agree with the concept that neither are deal makers or deal breakers within a boat you might like and cannot conceive the thought of retrofitting one to the other for the benefits or risk of one over the other.
Having said that, if I were looking at two boats that were otherwise identical, I would choose the keel cooled, dry stack boat. While I don't really lose sleep over it, no saltwater inside of a boat and no thru hulls tips the balance of plus and minus of each for me personally. That could be related to the build materials I prefer.
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Old 10-28-2020, 11:07 AM   #26
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OD have a lots of questions aand hope you can address them.
Hear of people opening the engine room door to heat the accommodations. Have you used this ploy to lower ER temps? In other words open that door let’s say 15 minutes before an ER check. If so does ambient air temp matter? Does that work in the tropics?
Have been lead to believe shaft output is more efficient with dry stack than wet exhaust. That you can run a lower HP engine and get same performance and greater range. Talking with local commercial lobster men and small stern trawlers they tell me that’s a reason they choose dry stack. Is there truth to that?
Over the years have had concerns with impellers, mixing elbows, heat exchangers and pumps. Service/replace at fixed intervals not waiting for failure. Can you offer any insight as to which set up is more expensive, time consuming and difficult to maintain?
Peter’s blog link was very appreciated. Did you have difficulties with engine room heat? How high did ambient temp go in your boat? What model nordhavn did you have? Did you do any modifications? Where did you cruise? Temperate?sub tropics? Tropics?
Thanks in advance and please anyone else with dry stack experience do chime in.
My Nordhavn was a 46, (dry exhaust) great boat for a couple and friends. It was destroyed in a shipyard accident.
My current boat is a AT34 with wet exhaust. It has 2 installed resistance heaters and I have one ceramic heater. Starting the engine to get warm is always an option.
I am in south FL so if it gets cold, I put on long pants, sweater and socks.
I know, if I get really cold, I can always run the engine with the access deck plates open and risk falling into the engine room. SMILE

The rest of this is just my opinion.
Efficiency is based first on boat designed, engine selected, speed, sea state, current etc.
I would not consider changing or modifying the exhaust without factory personnel.
Wet or dry exhaust, each have their own set of maintenance situations.
Which is better? You pretty much have to accept what was on the boat originally, by design.
I think I answered all your concerns, if not ask again.
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Old 10-28-2020, 11:22 AM   #27
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Now I HATE changing impellers, especially bigger ones in main engines. You get salt water all over everything, .....
This is why I always do a fresh water flush before changing the impeller (or any other work on the raw system). Much better to spill fresh water inside than salt. On a large boat with a good watermaker, you don't even need to be at the dock to do this. It doesn't take that much fresh to flush well beyond the raw pump.
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Old 10-28-2020, 12:12 PM   #28
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This is why I always do a fresh water flush before changing the impeller (or any other work on the raw system). Much better to spill fresh water inside than salt. On a large boat with a good watermaker, you don't even need to be at the dock to do this. It doesn't take that much fresh to flush well beyond the raw pump.

I'd like to do something like that. How do you have things plumbed up to do the fresh water flush? I think there are lots of ways it could be done, and I'm always interested in examples and how well they work.
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Old 10-28-2020, 12:39 PM   #29
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I'd like to do something like that. How do you have things plumbed up to do the fresh water flush? I think there are lots of ways it could be done, and I'm always interested in examples and how well they work.
Each vessel is different. Access is good on our DeFever making the impeller change out and clean up task not too difficult.

What I do on ours is close the through hull, drain the engine raw water by opening the little petcock on the bottom of the strainer and have a bit of fresh clean up water available for mopping up any released raw water when impeller cover is removed. Ditto the genset.
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Old 10-28-2020, 08:12 PM   #30
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Don't forget that after you clean the soot off your decks your dock neighbors may be asking you to clean your soot off their decks, and some not so nicely.
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Old 10-29-2020, 01:22 AM   #31
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A dry exhaust is frequently just a truck muffler welded in place.

Folks preferring a quieter exhaust should look up "hospital critical" mufflers .

There not light , not cheap, but do a great job of quieting , especially since few cruisers are at full throttle for very long.


https://www.industrialexhaust.com/silencers.php is one of dozens of choices.
Mine must of been from a Henry Ford era truck. It was loud. Loved the look of a big exhaust pipe coming up out of the deck. Looked like...a man boat.
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Old 10-29-2020, 06:37 AM   #32
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IMO if you're building a metal hull then dry exhaust is a no-brainer. Split pipe welded against the hull, or even full pipe held proud from the hull, is easy enough to clean during monthly scrubs.

However, dry exhaust with a fiberglass hull means either full pipe held proud, requiring brackets and dozens of holes in your hull for bolts to penetrate, or a gridcooler, which has its own constant challenges to clean inbetween the fins as was mentioned earlier.

Conversion makes little sense unless someone is going through an absolutely major refit or is converting a fishing boat to a cruising (for example).
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Old 10-29-2020, 07:20 AM   #33
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Running the engines exhaust pipe thru one of the many multiple wall SS pipes made for wood stoves or fireplaces solves the hot exhaust problem.

Only downside is building in a heated hanging locker using the heat from the exhaust system is almost impossible.

Folks that live aboard and wish to use their vessel when the bay is ice free will enjoy the ease of winter operation , with no winterizing.
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Old 10-29-2020, 08:04 AM   #34
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Is the keel cooler sufficient to avoid the need for bubblers?
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Old 10-29-2020, 08:09 AM   #35
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Some years ago a Nordhavn owner sold his N62 with a JD diesel and ordered a new Nordhavn with a Detroit Series 60. Both vessels were dry stack. When delivering the new N from Dana Point to BC the soot was very bad causing exterior soft cover and gel coat damage.

The new vessel could not be berthed next to other yachts due to sooting issues and liability. Very soon after delivery to the new location the Series 60 was removed from the new vessel ($$$) and a JD similar to his old N62 installed. Problem solved.

Two years ago the owner of a newly acquired dry stack paid for major cleanup on 5 vessels including ours. The marina told him to relocate his boat. I've a friend who placed a nylon stocking over his N57 dry stack to catch the soot before entering the Anacortes marina. He sold the boat.

For many dry stack is not always neighborly. Shop carefully as not all dry stacks are created equally.
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Old 10-29-2020, 08:26 AM   #36
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My 1989 46Nordhavn with dry stack, Lugger engine never caused a problem.
As much as possible we ran WOT outside from Long Island to Ft Lauderdale.
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Old 10-29-2020, 09:16 AM   #37
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Been a learning curve looking at small Nordhavns to buy. See some with twin turbo yanmars which are wet exhaust but most with naturally aspirated luggers to a dry stack . The small commercial fish boats around here commonly have truck or agricultural pump diesels repurposed for marine use with dry stacks. Now new trucks are nearly all common rail. Wonder if it makes any difference (NA, turbo, common rail) as too amount of soot at start up. Would think it would be a non issue with common rail.
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Old 10-29-2020, 09:20 AM   #38
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More modern diesels will soot less. But there will often still be some soot in the exhaust system over time. If the dry stack allows that soot to get wet in the rain, or accumulate in a spot where it can get blown out at the next startup, then you may get soot splattered around at startup. I'd say it depends as much on the exhaust system design as it does on the engine itself.
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Old 10-29-2020, 09:45 AM   #39
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A lot of factors are involved, but I think it’s an accurate statement to say common rail smoke Quite a bit less than mech injection (Especially If the engine is older). I say that after using both types of engines. I spoke to Tony Athens on the phone about this subject about 4 years ago and that was his opinion as well, which counts a heck of a lot more than mine. With that said, after reading this thread I would go with a wet exhaust over a dry on a new build if both options were available.
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Old 10-29-2020, 11:02 AM   #40
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Some years ago a Nordhavn owner sold his N62 with a JD diesel and ordered a new Nordhavn with a Detroit Series 60. Both vessels were dry stack. When delivering the new N from Dana Point to BC the soot was very bad causing exterior soft cover and gel coat damage.

The new vessel could not be berthed next to other yachts due to sooting issues and liability. Very soon after delivery to the new location the Series 60 was removed from the new vessel ($$$) and a JD similar to his old N62 installed. Problem solved.

Two years ago the owner of a newly acquired dry stack paid for major cleanup on 5 vessels including ours. The marina told him to relocate his boat. I've a friend who placed a nylon stocking over his N57 dry stack to catch the soot before entering the Anacortes marina. He sold the boat.

For many dry stack is not always neighborly. Shop carefully as not all dry stacks are created equally.
True dat Tom. Some engines seem better suited for dry stack than others. My CAT 3306 runs quite clean, but if the boat was powered by a 3208 I might feel differently, and if a DD my neighbors might cringe at my approach. I've had to clean soot off the top deck about 10 times in 15 years, and then because I didn't run the boat up to 80% of max RPM for a few minutes to blow out any accumulation of soot before turning into anchorage or a marina. The boat is quiet underway because it is well muffled, and the stack house is well insulated. The system seems pretty much bullet proof, at least so far. As TT said, excess heat from a dry stack seems a matter of not insulating the exhaust in the ER; mine isn't hot enough not to be able to touch.


The genset is hybrid - keel cooled and wet exhaust, and I've cleaned more soot off the side of the vessel where the exhaust loop exits than the top deck.


Converting a wet exhaust system to dry seems a bit pointless as both systems, if designed from scratch, work just fine.
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