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Old 01-17-2019, 06:40 AM   #81
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I believe "soot" is left from incomplete combustion.

To get rid of soot , no periods of ideling "warming up the engine" or running it because it has been a month since last operated.

TOO Light loading will cause soot as well as slobbering and loss of compression long term.

These are operator errors , not stack location problems.
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Old 01-17-2019, 06:56 AM   #82
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There have been several comments here about soot problems with dry stacks: blowing all over the boat; coating electronic gear and antennas, etc. But this seems to me to be mostly a poor design issue, especially with the Nordies, because the stack is center-mounted and to make things worse, is combined with the nav-stack.

Just looking at the photo you can see how there would be air turbulence and vortices coming off that mast. It's not even streamlined in shape. Plus the pilothouse/deckhouse below causes all sorts of vortices and eddies, thus likely sucking soot down. If one is sailing downwind then you can imagine the problem is even worse.

Look at the example fishing boat photo where the dry stack muffler is mounted at the side of the deckhouse, thus allowing the exhaust to extend all the way to the widest beam, to the gunnel, perhaps even extending slightly beyond that. Honestly I would recommend the exhaust in the photo be a couple of feet higher and wider to the gunnel. This allows the exhaust to exit into clean air. If the wind comes from astern, then likely the exhaust smell and soot will (mostly) miss the rest of the boat's structure.

One suggestion I would make to anyone wanting to build a Nordy with the centerline stack as shown, would be to have the engineers design those two side platforms (which support the TV and satellite domes) as NACA airfoils, upside down, of very high lift design for airflows of 10-30 knots. The air as it leaves the airfoils will naturally be drawn upward (updraft). For all you airline pilots you're familiar with the downdraft caused by air exiting your wings. This will in effect help to pull the exhaust upward and away from the boat.

Of course it won't help when the boat is sitting at mooring, no wind, and you first startup and then the dry soot blows out. But it would be better than doing nothing.

BTW, yes, I did test this in wind tunnels when I was studying for my aero engineering degree many many moons ago



All good points. But keep in mind that ground wind speed is typically higher than boat speed. So regardless of design, when the wind is blowing in the right (wrong) direction, the exhaust plume will be against the stack and instrument structure no matter what. All our issues were with a strongish tail wind, blowing the plume forward across everything.


A side exhaust like the work boat could well solve the problem of soot on instruments. Actually, anything that creates more separation would help. As I recall, Delfin's boat has good separation and he hasn't had any issues.


When citing workboats as validation for dry exhaust, I think it's important to keep in mind that dirt and grime is much less of a concern on such a boat.
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Old 01-17-2019, 07:16 AM   #83
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When citing workboats as validation for dry exhaust, I think it's important to keep in mind that dirt and grime is much less of a concern on such a boat.

Very funny and very true point. Another reason why you should have your boat painted camouflage grey and black
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Old 01-17-2019, 08:38 AM   #84
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The primary reason for smaller commercial vessel dry stack applications is the challenge a wet exhaust faces with highly variable water lines due to cargo weight variations. Add to that an intentional side or stern flooding situation as loads are lifted on and off when at sea, wet exhaust simply won't work.

As an aside I've been plowing through a backlog of boating magazines left over from 2018. In the dozens of magazines I've discarded containing more than probably 200 boat reviews and tech articles, none have had dry stack nor even discuss it. Including several new Nordhavns. It would appear in the recreational world, dry stack is a non subject.
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Old 01-17-2019, 08:46 AM   #85
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The primary reason for smaller commercial vessel dry stack applications is the challenge a wet exhaust faces with highly variable water lines due to cargo weight variations. Add to that an intentional side or stern flooding situation as loads are lifted on and off when at sea, wet exhaust simply won't work.

As an aside I've been plowing through a backlog of boating magazines left over from 2018. In the dozens of magazines I've discarded containing more than probably 200 boat reviews and tech articles, none have had dry stack nor even discuss it. Including several new Nordhavns. It would appear in the recreational world, dry stack is a non subject.
Where I live most fishing boats with dry exhaust is to keep the fumes away from the work deck and to avoid freezing. There are some lobster boats with wet that primarily operate in the warmer seasons but loading isn't an issue as they carry full loads of traps and a full lobster tank with no problem.
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Old 01-17-2019, 08:56 AM   #86
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Where I live most fishing boats with dry exhaust is to keep the fumes away from the work deck and to avoid freezing. There are some lobster boats with wet that primarily operate in the warmer seasons but loading isn't an issue as they carry full loads of traps and a full lobster tank with no problem.
I agree. Variable water lines do indeed exist though, common in fact. Some commercial buddies in AK will have an easy 8" -12" swing at rest as loads are lifted off, holds/tanks serviced and fluids/ice added. No place for a wet exhaust.

A very happy day for us was a few years ago when the dry stack vessel, with an old DD, berthed next to us permanently departed his dock.
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Old 01-17-2019, 02:07 PM   #87
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Steve,

It was an East Coast NL dealer in reply to a query I had about the number of NOS NL heat exchanger cores available. Maybe I misunderstood was he was telling me. He was referring to workboats.

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Paul,

Maybe he understood this to be true but I can assure it is not, it's rare indeed, pleasure, commercial, etc, NL makes very few KC gensets.

Underwater exhaust using a water gas separator, on the other hand, as Delfin surmised, is very common. It can be installed with any generator.
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Old 01-18-2019, 06:53 AM   #88
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KK and dry stack is about the only way any vessel can be used frequently in below freezing weather.

Unless fully manned 24/7 and all compartments are heated and inspected.

The LI Sound delivery posts show the huge fear/reluctance to operate in winter by most recreational boaters.

Once the vessel is outfitted for winter use , it is a delight .
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Old 01-18-2019, 07:50 AM   #89
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Good point FF. Overheating of engines is a real problem with arctic and antarctic vessels. Keeping the sea chests clear of ice, whether via heating or constant attention, is a big issue.
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Old 01-18-2019, 08:09 AM   #90
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Since we enjoy thread drifting, I've been PNW long distance boating in -10F weather with wet exhaust, no problem. But in LI Sound and marinas , nope too much ice for our yacht hulls, so why do it?.
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Old 01-18-2019, 11:00 AM   #91
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Since we enjoy thread drifting, I've been PNW long distance boating in -10F weather with wet exhaust, no problem. But in LI Sound and marinas , nope too much ice for our yacht hulls, so why do it?.
Oops, should have said +10 F.
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Old 01-21-2019, 07:15 PM   #92
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Interesting solution to a dry exhaust through a fibreglass hull. It does exit above the waterline but it is routed in a trough through the hull to allow the water to cool the pipe. The exit point below the waterline is insulated from the hull.
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Old 01-21-2019, 09:07 PM   #93
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Steve,

Maybe I misunderstood about the number of keel cooled NL’s but what he told me is that the installers pull the heat exchanger tubes out of the generators and run them with coolant. I think the spare heat exchangers were called “pull outs” in the trade and that is why they are available cheaper than new ones. And I should say more available as well because sourcing some NL spares can be tricky at times.

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Old 01-22-2019, 02:23 AM   #94
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The removed heat exchanger tube bundles, take outs, makes sense. The failure rate on those, NL's anyway, is extremely low, so I'd imagine they sit on the shelf for a long time.
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