Exhaust insulation

[SP3]

Hello Trawler Forum,

This is my first post, I have been lingering on the sidelines for a while and found some great information here. So I have a lot of time on the water, but just jumped into ownership and have been running through the survey trying to clean up some issues.

The boat has a dry stack and I have ordered a pro-done insulation (lace up) to fit around the exhaust elbow up into the engine room ceiling to a coupling in the muffler closet (I don't have a better name for it). I have the panels removed on the muffler closet and there is a nice sized muffler sitting where I can easily access it. The surveyor says I am fine not going any further with the insulation (the muffler closet has some sort of insulation board) with 2 to 6 inches of space on the sides.

So my question is: should I add some rockwool in that space. Noise is not much of a problem currently, but if that would noticeably deaden some sound, it may be worth the cash and effort.

The other question - If I run my car on a road trip, say 4 hours plus, the carbon burns out of the exhaust pipe and the inside of the pipe is whitish. When we start the engine on the boat, some black carbon flakes fly out on the deck. So would insulating the muffler closet help decrease that by keeping the exhaust system hotter? Seems like we are 4 hours from everything, so there is plenty of run time.

Or should I just close that panel up and check that off the list?

 

[Comodave]

I would not add insulation around it. I think it is pretty normal for dry stack exhaust systems to blow out some soot. Oh, BTW, welcome aboard.

 

[hollywood8118]

Hello Trawler Forum,

This is my first post, I have been lingering on the sidelines for a while and found some great information here. So I have a lot of time on the water, but just jumped into ownership and have been running through the survey trying to clean up some issues.

The boat has a dry stack and I have ordered a pro-done insulation (lace up) to fit around the exhaust elbow up into the engine room ceiling to a coupling in the muffler closet (I don't have a better name for it). I have the panels removed on the muffler closet and there is a nice sized muffler sitting where I can easily access it. The surveyor says I am fine not going any further with the insulation (the muffler closet has some sort of insulation board) with 2 to 6 inches of space on the sides.

So my question is: should I add some rockwool in that space. Noise is not much of a problem currently, but if that would noticeably deaden some sound, it may be worth the cash and effort.

The other question - If I run my car on a road trip, say 4 hours plus, the carbon burns out of the exhaust pipe and the inside of the pipe is whitish. When we start the engine on the boat, some black carbon flakes fly out on the deck. So would insulating the muffler closet help decrease that by keeping the exhaust system hotter? Seems like we are 4 hours from everything, so there is plenty of run time.

Or should I just close that panel up and check that off the list?

DO NOT fill the plenum space around the dry stack, it will get very hot and possibly cause a fire!. The plenum needs air movement to cool itself.
Lots of dry stack boats dump some soot on the decks, that's their biggest negative attribute.
Is the boat a N46?
HOLLYWOOD

 

[Keysdisease]

The addition of rockwool will probably not result in a noticeable reduction of noise and may create the situation Hollywood describes. Something else is that the open space around the muffler may be part of the supply air design to bring combustion air to the engine room.
Rock wool is incombustible, and usually has 6 to 8 lbs of density per cubic foot. Mass is what stops sound, rockwool is an noise absorber and incombustible thermal insulation. What you want is a noise barrier, either lead on the inside or mass loaded vinyl (MLV)on the outside of all panels of your exhaust trunk that are common with accommodations.
For example, if your exhaust trunk is integrated into the aft bulkhead of your pilothouse, you would insulate the 2 sides and the front if they are in the pilot house, and probably not the back because it may abut the aft weather deck.
To use lead you would not want to cover your existing insulation, which is your absorber layer, so you would need to remove that, install lead sheet, and re-install the existing insulation. You could install mass loaded vinyl on the outside of the trunk and cover it and that would be just as effective as lead on the inside, if the MLV and lead were same/same weight per sq ft.

 

[trawlerjeff]

exhaust insulation

My dry stack exhaust plenum utilizes a bilge type fan to blow engine room air up the surrounding exhaust plenum to a dorade vent. This insures low temperature to the surrounding structure.
I have never experienced soot from my stack, possibly due to the fact that I cover the outlet of the stack with a boot type canvas to protect from rain entering the exhaust, just my thought. Jeff

 

[SP3]

Great responses. It doesn't sound like I can expect much of a result for the effort, so it is is option three. Close it up and move on.

There is a parallel space with two air intakes and what appears to be a "chimney" to the outside, so the air circulation is accounted for there. The whole exhaust was uninsulated and the surveyors where most concerned about the heat source in the engine room. He wasn't concerned about the plenum, the panels are 3 to 4 inches thick and are doing a good job keeping noise down and the heat out. It is powered by a Deere, so I assume is pretty good natured about noise to begin with.

There is a sleeve that slips over the exhaust outlet, I'll make sure that is always put back, hopefully that helps as well. Sounds like someone will be swabbing the decks when we go out.

It is not an N46 (Nordhavn?), it's a commercial conversion.

 

[C lectric]

I too have a dry exhaust. Mine exits on the back deck so no closet. However there is a SS enclosure around the mufflers. The space between the mufflers and the enclosure is left open, no insulation, and the top is also open to the air with a cover to exclude rain.

This way air engine compartment air exhausts out the E.C. at the top of the enclosure which cools the mufflers and piping.

I too cover the exhaust tip to exclude any rain when not operating which helps hugely preventing the rain from loosening soot.

Once in a while I will crank up the rpm well above my normal cruise rpm to not only heat the engine but also the stack. Done for maybe 10 minutes. The heat and increased exhaust flow will blow out any loose soot. As long as I do that periodically I don't get the decks sooted.

Be sure the air cleaners are clean. Then engine will run with somewhat dirty air cleaners but at the expense of a dirty burn.

Last and NOT least is make sure the prop is allowing the engine to reach it RATED RPM. TO make EG. 8m knots it takes X amount of HP. If the prop is overpitched the engine still has to make that HP but it has to do it at a lower rpm which means less air but the same fuel. TO a point this can be done

BUT if the prop is pitched correctly the engine may be running a hundred or two hundred rpm faster to make that 8K but each cylinder firing uses less fuel, there are just more of them and the air supply is improved.

Poorly worded maybe but I observed my own boat before and after a repitch some years ago. The exhaust was much lighter at the same boat speed but the engine ran at about 150 rpm more to do it.

 

[Xsbank]

Explain to me how wrapping an exhaust pipe with insulation can cause a fire in the "chimney?" That simply makes no sense. Mine has been wrapped for 7 years, rock wool with aluminum tape. The chimney is made of plywood inside of aluminum plate and so far nothing has burst into flames. In fact, you can put your hand on the exhaust pipe and it's just warm.