Exhaust questions

[Jeff Lebowski]

I notice that some boats use a dry-stack while others, I assume release exhaust gas and cooling water out the transom. What are the benefits of the dry stack? I assume that it's cheaper over time since there is no cooling water to move around and eat at metal bits?


And when running at trawler cruising speeds, is exhaust the smelly issue that it is on a sports fisherman while trolling?

 

[rslifkin]

Smell issues depends a lot on how air moves around the boat and exactly where the exhausts discharge. Some setups will pull fumes back onto the aft decks under certain conditions (running fast into a headwind can be the worst with transom exhausts).

Dry stacks are simpler, provided you have keel cooling (which would eliminate the raw water system). But they're often a bit louder, sometimes have issues with blowing soot onto the decks at startup, they consume interior space for the airspace around the pipe going up, and if you don't go with keel cooling, they don't really save any complexity.

 

[Lepke]

As above: noticeable exhaust fumes depend on where it's released and the wind direction. Nothing is perfect.

Dry stacks put out lots of heat where they pass thru a cabin. And it's hard to insulate enough to negate the heat and noise. You see dry stacks on ships and commercial boats where they have room to insulate or don't care as much about crew comfort. All dry stacks spit out at least some soot. Any water that forms on the exhaust pipe when cold is picked up and goes out as drops before the exhaust is hot enough to evaporate it.
I've been on many vessels with differing exhaust, I like the stern wet exhaust much better than dry stack. But I like underwater exhaust best of all.

 

[mvweebles]

20+ years ago, in the wake of Beebe, dry stack was the alter at which trawlerites worshipped.

No more.

There are pluses and minuses to wet and dry, and either can be reliable when properly installed and maintained.

Dry stack in a hi-end trawler is expensive to design and install. While no water is required to cool the exhaust, very strong blowers are often required. Pick your poison.

I wouldn't pick a boat based on exhaust. But if I were doing a new build, chances are I'd go wet.

Peter

 

[Jeff Lebowski]

Slam dunk replies. Thanks to all.

 

[FF]

Besides simplicity the dry stack + keel cooling allows a boat to be operated in freezing conditions , docked and left with no winterizing required. Allows a liveaboard to enjoy winter cruising ,,with no effort.

The double wall and now triple wall home fireplace stove pipe eases exhaust heat concerns , although one advantage of a dry stack is the ability to have a heated hanging locker to dry out gear.

By not having a sea water circuit all the hassle of chasing rubber pump bits out of the engine and heat exchanger is forever gone ,as is the plugged inlet hassle.

Noise from the exhaust is cured by installing a "Hospital Critical" grade exhaust muffler .

If you are lazy like me the dry stack + keel cooling is a one time expense , maintaining a wet exhaust is always work and cash.

 

[mvweebles]

Besides simplicity the dry stack + keel cooling allows a boat to be operated in freezing conditions , docked and left with no winterizing required. Allows a liveaboard to enjoy winter cruising ,,with no effort.

The double wall and now triple wall home fireplace stove pipe eases exhaust heat concerns , although one advantage of a dry stack is the ability to have a heated hanging locker to dry out gear.

By not having a sea water circuit all the hassle of chasing rubber pump bits out of the engine and heat exchanger is forever gone ,as is the plugged inlet hassle.

Noise from the exhaust is cured by installing a "Hospital Critical" grade exhaust muffler .

If you are lazy like me the dry stack + keel cooling is a one time expense , maintaining a wet exhaust is always work and cash.

Those are the traditional arguments against Wet and for Dry. Our own TwistedTree, a serial Nordhavn owner, went Wet on his newest build (an N68 if I recall). His arguments for Wet were compelling to me - not the least of which is that while raw water pump requires service, so too does a keel cooler which can be difficult to clean. The raw water pump is at least inside the boat and easy to service.

I don't know what percentage of Dry installations on trawler yachts require blowers to cool the stacks, but these industrial-sized 120/240VAC blowers are large, noisy, and relatively expensive. Granted, if a blower goes out you can still limp-along at idle-forward I suppose, but I doubt they are anywhere near the reliability of an engine-mounted raw water pump with no electrical motor to fail.

I guess my point is the mythology of Dry stack for trawler yachts is a bit over-blown. Yes, the bulk of the world's small vessel fishing fleets run dry stacks. But those systems bear little resemblance to the carefully curated and engineered systems on modern Dry-stack trawler yachts such as Nordhavn. Great systems no doubt, but the Wet versions are too.

Peter

 

[rslifkin]

For a wet system in freezing weather you'd just have to design the system well. Exhaust ports far enough above the waterline to never be submerged at rest. Configure the system so the pipes and such outside of the engine room drain at shutdown. Maybe even have the mufflers drain at shutdown. Install engine block heaters to keep the heat exchangers and plumbing on and near the engines warm. Then it's only an issue if you need the boat to sit without power available.

 

[Bmarler]

we always had dry stacks on the fishing boats up north. i never asked my dad why, i just thought all boats came that way. it could have something to do with the sheer number of hours clocked on the engine while trolling around, no impeller to worry about. we didn't have much to do on the keel coolers that i remember. the stack usually kept the diesel exhaust high overhead when working the lines too.
would i want it now? 50/50 i guess. it does take up interior space having it run up top. not scrubbing soot off the transom has a certain appeal too.

 

[Greg S]

…

I don't know what percentage of Dry installations on trawler yachts require blowers to cool the stacks, but these industrial-sized 120/240VAC blowers are large, noisy, and relatively expensive. …[/ QUOTE]


I’ve never seen a blower like you describe on a dry stack boat. What is it for?
If for ventilation, it’s a waste of time. Every dry stack I know of has the exhaust pipe inside a larger pipe. The hot exhaust pipe induces a substantial air flow due to rising thermals. Cold air inlets are always directed to the lower areas of the bilge. Hot air rises right out the stack.

Maybe in the tropics?

 

[FF]

A proper designed keel cooler will handle full throttle in tropical waters with a load of fouling on an external cooler.

As they cool "too much" in most normal operation a bypass thermostat is used to maintain a constant coolant temperature.

Metal boats can have the cooler inside the hull , for less possibility of damage

 

[mvweebles]

…

I don't know what percentage of Dry installations on trawler yachts require blowers to cool the stacks, but these industrial-sized 120/240VAC blowers are large, noisy, and relatively expensive. …[/ QUOTE]


I’ve never seen a blower like you describe on a dry stack boat. What is it for?
If for ventilation, it’s a waste of time. Every dry stack I know of has the exhaust pipe inside a larger pipe. The hot exhaust pipe induces a substantial air flow due to rising thermals. Cold air inlets are always directed to the lower areas of the bilge. Hot air rises right out the stack.

Maybe in the tropics?

I can't speak for recent, but Nordhavns had large industrial Delta blowers to exhaust heat from engine room and exaust stack.

George Beuhler originally specified dry exhaust for the Diesel Ducks - it was good for marketing too. When Seahorse built the first steel 38, they could not effectively disappate heat. They tried a number of changes to remediate the issue, then finally just went with wet exhaust out the side of the boat.

Diesel has 135,000 Btu per gallon - over 400,000 Btu if 3-gph. Sure, some goes to energy to move the boat, some gets transferred to a keel cooler, but combustion generates a lot of heat (that's sort of the point of combustion) so somehow all that heat has to be shed - not all of it goes out the stack. Expecting that much heat to passively escape via a fairly small chimney/stack via thermals is unrealistic.

Peter

 

[mvweebles]

A proper designed keel cooler will handle full throttle in tropical waters with a load of fouling on an external cooler.

As they cool "too much" in most normal operation a bypass thermostat is used to maintain a constant coolant temperature.

Metal boats can have the cooler inside the hull , for less possibility of damage

Quite right. But keel cooler does nothing to cool exhaust gas.

Peter

 

[FF]

"Quite right. But keel cooler does nothing to cool exhaust gas."

True , but with double wall , and now triple wall SS fireplace exhaust tubing available it should not be a hassle.

And of course Plan B , run the exhaust outside , as many commercial boats do with a simple heat shield is the low cost cure.

 

[FF]

Folks that worry about dry stack soot can install a filter, or tune up the engine.

The soot is products of incomplete combustion , a boat with only 2 or 3 cruising RPM should be able to set the boat up to burn clean.

https://www.nettinc.com/products/diesel-particulate-filters-dpf/greentrap-volt-active-dpf.

 

[Scooby5959]

20+ years ago, in the wake of Beebe, dry stack was the alter at which trawlerites worshipped.

No more.

There are pluses and minuses to wet and dry, and either can be reliable when properly installed and maintained.

Dry stack in a hi-end trawler is expensive to design and install. While no water is required to cool the exhaust, very strong blowers are often required. Pick your poison.

I wouldn't pick a boat based on exhaust. But if I were doing a new build, chances are I'd go wet.

Peter

In the process of converting my exhaust to keel cool dry exhaust as we speak . Yes on my tiny Nordic 26 , keel cooler has been ordered and probably is on its way so we shall see , my engine compartment is quite small and I’m doubling down with a dry exhaust manifold as well .I’m not real confident that won’t be an issue . If I can’t solve the manifold heat issue I will order a water cooled exhaust manifold but after doing some research I determined that I should be able to deal with it .Cummings has a marine engine that comes stock with a dry manifold and turbo, It’s north of 300 hp ,there’s been some reported issues with it but the outfit that I bought my keel cooler from are expert on marine manifolds they make a manifold for practically every engine out there .His recommendation was to have it ceramic coated and insulated , he said he thought it would work out fine . like I said this is the outfit out of Alabama nobody knows more about manifolds than this outfit to be continued

 

[FF]

"If I can’t solve the manifold heat issue I will order a water cooled exhaust manifold but after doing some research I determined that I should be able to deal with it .

Wrapping with insulation is a good option along with increasing the engine room cooling.

There are also companies that create insulated manifold wraps for different engines.

 

[mvweebles]

In the process of converting my exhaust to keel cool dry exhaust as we speak . Yes on my tiny Nordic 26 , keel cooler has been ordered and probably is on its way so we shall see , my engine compartment is quite small and I’m doubling down with a dry exhaust manifold as well .I’m not real confident that won’t be an issue . If I can’t solve the manifold heat issue I will order a water cooled exhaust manifold but after doing some research I determined that I should be able to deal with it .Cummings has a marine engine that comes stock with a dry manifold and turbo, It’s north of 300 hp ,there’s been some reported issues with it but the outfit that I bought my keel cooler from are expert on marine manifolds they make a manifold for practically every engine out there .His recommendation was to have it ceramic coated and insulated , he said he thought it would work out fine . like I said this is the outfit out of Alabama nobody knows more about manifolds than this outfit to be continued

What problem are you trying to solve? Will be interested in before/after pictures of your PH.

 

[Scooby5959]

Just received my drye exhaust manifold quite impressed heavy duty cast iron including the elbow also gaskets everything ship to my door $83.45 genuine perkins parts wow I figured for that price it would be cheesy knock off no Genuine Perkins ,fuel inject pump marine dealer $2200 tractor dealer 920 bucks I’m starting to like this perkin Don’t need one but I looked anyways ,we’ll see after I get the dry exhaust done ,I can put whatever engine I’d like in ,Maybe I won’t need two, parts are plentiful and cheap

 

[Scooby5959]

I’m thinking about starting a thread about this but I don’t know I get tired of defending myself Because I have strong opinions, we’ll see I’ll try to get some pictures

 

[Scooby5959]

Still waiting for my keel cooler and my motor mounts ,then I can put things back together right now it’s blocked up waiting for motor mounts

 

[Scooby5959]

What problem are you trying to solve? Will be interested in before/after pictures of your PH.

My exhaust system needed to be replaced so I thought if I was going to replace it I might as well go dry. It will make it much easier to re-power if I need to down the road you can re-power for 1/3 of the cost of an Typical marine engine . A 35 hp Kabota industrial engine is less than $6000 brand new with a warranty ,you can buy the necessary parts To adapt my existing transmission or another one for a few hundred dollars.Plus a baby tug needs a respectable dry exhaust .I thought I would enjoy the process .You called it a character Boat whatever that is a dry exhaust might give it more character

 

[CharlieO.]

You called it a character Boat whatever that is a dry exhaust might give it more character

Maybe 'character' boat was referring to the operator. I'll be interested in the finished product with the dry stack and if you decide to repower.