Why wet or dry exhaust not in specs?

[ddw36]

After looking at numerous listings for trawlers of 42 or so feet, I notice the specs do not indicate whether the exhaust system is wet or dry. My preference, after reading up on the subject, is a wet system. I know I could contact the broker/seller re: this, but having to call numerous parties on this one item is a pain.



For me, a boat would have to be desirable in every other respect for me to accept it with a dry exhaust. IOW, it's a deal breaker for me. So, why is this feature not listed in the specs on used boats? I am not asking the merits of dry vs wet systems.

 

[guy with a boat]

Wet exhaust is so much more common, at least on recreational boats, that its pretty safe to assume that’s what is there unless it specifically says otherwise. It’s often not mentioed because that is the norm and those that have a dry stack will likely tout it as the advantage that it can be.

 

[Comodave]

Yes, it is very unusual to find a dry exhaust in a 40’ pleasure boat. Maybe a couple in a hundred???

 

[FF]

For many folks Keel Cooling and a dry exhaust are considered a huge upgrade over a wet exhaust.

Any seller would tout this advantage in a sales advertisement.

It is the only way a vessel can be used in freezing weather without a complete winterizing regime every evening.

 

[mvweebles]

To OP: why is dry exhaust a deal breaker for you? Just curious - many trawler folks lean the other direction which is why dry exhaust is prominently featured in boat ads. Also, it's pretty hard to hide a dry stack in a photo. I'm not looking to spin up a dry/wet holy war, just wondering about your thinking.

Thanks in advance.

 

[Woodland Hills]

You are pulling our leg right? If not, just look at the pictures of the boat.

 

[mvweebles]

For many folks Keel Cooling and a dry exhaust are considered a huge upgrade over a wet exhaust.

Any seller would tout this advantage in a sales advertisement.

It is the only way a vessel can be used in freezing weather without a complete winterizing regime every evening.

No reason a wet exhaust boat can't have keel cooling. Yes, still pumping water to inject into the exhaust, but engine itself is cooled via an external cooler (in short heat exchanger is relocated to outside of hull) . As an aside, virtually all dry stack recreational trawlers require sizeable blowers to cool the stack - lose the blower and there's a serious heat problem. Not unlike losing a raw water circulation pump. Just depends on whether you believe an electric blower is more reliable than @an impellor pump.

 

[diver dave]

... As an aside, virtually all dry stack recreational trawlers require sizeable blowers to cool the stack - lose the blower and there's a serious heat problem. Not unlike losing a raw water circulation pump. Just depends on whether you believe an electric blower is more reliable than @an impellor pump.

I would think those options would both be inferior in reliability/maintenance to an insulation wrap and passive venting.

 

[mvweebles]

I would think those options would both be inferior in reliability/maintenance to an insulation wrap and passive venting.

You would think. In an earlier life, I was a delivery skipper and delivered about 20 Nordhavns to various destinations. They all had massive A/C blowers to evacuate exhaust heat. I personally never experienced a failure but my understanding is sisterships are severely handicapped in the event of a blower failure.

Another example: Seahorse-built Diesel Ducks are wet-exhaust. They didn't start that way. Originally, the owner of the Seahorse yard wanted dry stack as he felt it made the boat more marketable as a long distance trawler (and I'm sure George Buehler, the designer, spec'd it). Hull #1 was brought on it's own bottom to San Francisco where I met the owner and spent a few hours with him where I gave him some docking tips (not a tremendously experienced owner, and not a lot of docking on the passage from Hong Kong). He described that, during sea trials, Seahorse just could not get the exhaust stack and engine room cooled. Eventually they gave up and converted to it to wet exhaust and punched the exhaust out the side of the engine room instead of leading it aft to exit the transom. Granted its been over 15-years since I talked with the owner of Seahorse, but at the time, he'd give up a child before he'd install another dry stack.

I'm not knowledgeable in the design of a dry stack so my experience is observation only. But it's first-hand observation, not dock-chatter. There appears to be more to a dry stack than just busting a hole in the roof and overturning a bucket on the stack to keep the rain out.

Personally, I like the idea of a keel cooler with a wet exhaust, though I was initially leery. The last Willard 40 was built for an exec of Willard Marine, and he had it built exactly that way. I accompanied he and his wife on a Baha Ha Ha from Long Beach to La Paz (~1000 nms or so) in 2005 or so, and I liked the setup a lot.

 

[Bkay]

If it doesn't say, assume wet.

My preference is dry if well designed. Wet if poorly designed. But part of that is a regional preference since I'm in an area where you can use a boat ALMOST year round if dry exhaust.

 

[Maerin]

My 43 Solo is one of those with keel cooler and wet exhaust. My engine has no seawater exchanger. Instead, engine coolant is circulated to the grid cooler that's mounted on the hull. It enables the engine to run with a 193F thermostat, so the diesel is happy with that. It does require that the grid cooler is cleaned about every 6 months to remove any shelling. It still is equipped with a seawater pump, its sole purpose is to provide seawater cooling of the exhaust which is a conventional system with mixer ell and water lift muffler. Because the Cummins 6BT is de-rated to 180HP from the typical 210HP, it requires no aftercooler, another maintenance source eliminated, as well as no zincs. De-rating also bumps the engine rating from intermittent (210HP) to medium continuous (180HP)


There's more to the engine service than wet/dry exhaust. Dry exhaust alone certainly should not put a boat in the "deal breaker" bin. I'm in the group that you need to select the boat based on how you're intending to use it, not by a few specifics like the exhaust that play a very secondary role in how your boat suits your style. Keep doing your homework.

 

[sunchaser]

Dry exhaust often means soot. Few recreational cruisers like soot. So just assume that once beyond most Nordhavns, dry exhausts are non existent for a recreational vessel.

 

[sean9c]

To the original question. I'd think that if there were pictures with the boat listing that it'd be pretty easy to determine if it's wet or dry exhaust.
To the idea of keel cooler and wet exhaust. I don't understand the why. You have the same number of water pumps and thru hulls but instead of engine heat exchanger maintenance, which is easy and done with the boat in the water you have keel cooler maintenance which may require a haul out. And you have the extra drag of an external keel cooler.
Soot at start up is a real issue with a dry exhaust. Soot on your neighbors boat might not be a big deal with commercial boats but what are you going to do when your dock neighbor with the fancy boat is complaining about soot from your stack on his teak decks?

 

[DCDC]

We have twin engines with dry stack exhausts and keel coolers. To some of the above points:

Through hulls: there are two through hulls per keel cooler but they are closed circuit and not open to the sea.

Drag: the coolers are low profile and close to the hull so drag is relatively minor.

Maintenance: other than changing zincs there is no maintenance. Construction is of a copper/nickle alloy so some inherent antifouling. We cleaned them once, without haul-out, over a one year, 2800 nm season.

Blowers: we have two intake fans, not high capacity blowers, to cool the engine room. The dry stack housings have vents at the bottom for passive convective cooling. The exhaust system is well insulated.

Soot: have not experienced any soot. We have an large,open aft deck so any soot would be immediately noticeable.

In summary we favor the dry stack/keel cooler for simplicity. No salt water pumps, strainers, exhaust mixing heads, knock-out pots, anti-siphon loops. Have had zero problems with the systems.

I can't recall seeing any commercial fishing, tug or service boats without dry stack exhausts, so assume this means they are economical and reliable.

Pictures attached.

 

[Island Cessna]

The best exhaust/cooling system I have owned was a 1938 built wooden cruiser with a Chrysler Crown gas engine, keel cooled, with wet exhaust. The exhaust had a lagged vertical pipe off the engine to well above the water line, with raw water from a tiny belt driven Jabsco pump injected in the down-coming pipe from that, then a rubber muffler and hose to the transom, all draining by gravity.
The keel cooler was bronze pipe fastened to side of the keel, and was maintenance free for many years. The raw water flow needed to cool the exhaust is a fraction of the flow needed to cool the engine with a heat exchanger, so that pump was small, slow turning, and trouble free.
This would be my “dream” system today.

 

[mvweebles]

DCDC - speaking of boat-porn! Nice system, nice setup. Question: why do you think some boats like Nordhavn need such big blowers? I realize it's probably good practice to have negative pressure in the ER, but they have massive blowers. I see your chimney chaseways run alongside the cabin sides versus through the salon/galley, do you think that makes a difference?

 

[DCDC]

Hello Weebles - I think you are right. I've been on a few Nordhavn's and seem to remember the stack chase going through the living areas. With twin engines our stacks are on the sides with most heat transfer to the outside. The insulated exhaust piping runs in heavy (3/4") aluminum chases which provide structural support for the risers, antenna arches and lateral paravane guys. We do notice some heat inside after long runs but not excessive.

 

[FF]

Today a dry stack is really easy to fit into a smaller boat.

The exhaust pipe pipe is lead inside a fire place SS multiple wall stack.

The biggest disadvantage is it runs too cool to build in a drying hanging locker.

 

[ddw36]

Belatedly, thanks to all who responded to my OP. Many pictures in ads don't clearly show whether wet or dry. That's why I posted, and I'm no longer able to physically shop for boats. Due to their dry exhaust systems, I would not own a Nordhavn, despite their excellent reputation in other respects. Narrow minded? Ok, but there are several other acceptable alternatives. Thanks, again.

 

[guy with a boat]

I will throw in some additional feedback for those interested other than the OP, since he seems to have made up his mind.

My boat has a dry stack on the main engine, and we have no soot, no perceptible heat in the living areas, no exhaust fan in the stack, and no other downsides that I can identify. The exhaust is wrapped and insulated and seems to carry the heat out the top with no issues. The engine room has intake and exhaust fans but radiant heat in the engine room is very noticeable from the engine itself but minimal from the exhaust.

Incidentally, the small wing engine has a wet exhaust and is noticeably louder when running compared to the main, despite being less than half the displacement.

I have had both systems on multiple boats and am a big fan of a properly designed dry stack on a trawler.

 

[sdowney717]

I have thought a keel cooler a great idea, but I changed my mind due to marine fouling.
Just my own view though.
Boats in some areas just love to grow so much on their hulls, it seems impractical and would be difficult to keep clean.