Generators and noise.

I have a Northern Lights 6.5kw gen set in an enclosure. The boat is A 2007 vintage, the gen set has 350 hrs. So I don’t use it much. When running, it is not overly noisy onboard, but there is the drone of it running. Outside of the boat it is very quiet. A few feet away from the boat and you barely know that it is running. I read posts of those who run gens several hrs a day, or all night to run AC as necessary. My question is, are there boats in the 40-60 ft range, where you do not hear the gen set running?

Regardless of how quiet it is, in the absence of any other noise, you will hear it running. That said, the fan on my air conditioner is louder than the generator in the forward master stateroom.

Ted

It could be the generator isn't isolated enough from the boats structure. Noise is picked up and resonating thru the hull. Usually the enclosure is fastened to the structure and the engine and generator head sit on rubber mounts. Putting vibration/sound material between the enclosure and the structure stops a lot of noise. A thick rubber pad underneath or maybe a honeycombed material. I'm old, there's probable newer stuff. Hard foam works good, but gives off toxic fumes when on fire.

Were at 90 feet and have large banks of battery's with inverters
Usually only run one Genny 60 kva for a couple of hours during dinner and after running dishwasher if anchored.
Never when at dock (unless the power is bad)

When we first got our boat and did the sea trial I didn't even know one was running when I boarded it
Only the exhaust gave it away

On bigger boats; a lot have small night generators that have a lot of sound proofing and the only thing you might hear is the exhaust from the outside of the boat

In our American Tug 435 we have a Northern Lights 9kW, factory-installed in the Lazarette which we also do not use very often. Since it is back there, of course there is a bulkhead wall between it and the engine room.
In full disclosure, the better half says my hearing isn't all that great but I can tell you when we start up the genny, I cannot tell if it started unless we open both the cockpit door and a lazarette hatch cover. Then if its running and those doors & windows are closed, we generally do not hear it.

Rebel112r said:

I have a Northern Lights 6.5kw gen set in an enclosure. The boat is A 2007 vintage, the gen set has 350 hrs. So I don’t use it much. When running, it is not overly noisy onboard, but there is the drone of it running. Outside of the boat it is very quiet. A few feet away from the boat and you barely know that it is running. I read posts of those who run gens several hrs a day, or all night to run AC as necessary. My question is, are there boats in the 40-60 ft range, where you do not hear the gen set running?

Click to expand...

My boat is a little over 60', and has 2 Onan 17kw eQD generators, in the lazarette just aft of the engine room. When starting either genset from the helm, if I listen carefully, and provided that the mains, TV/radio are not on, I can hear the increase in background noise. Once it is running, I have to listen very carefully to hear but the genset. The salon is over the engine room (forward of the lazarette) and the gensets are just as hard to hear from there. Even in the cockpit (above the lazarettes), you have to listen to hear the genset running, and you are more likely to hear the splashing of exhaust than actual combutsion noise. In fact, the generator is so quiet, that I have left the boat forgetting to turn them off. The generators can be heard pretty easily in the crew quarters, which are just forward of the lazarettes, aft of the engine room. But it isn't objectionably loud, and with the mains running the genset noise cannot be heard anywhere on board.

Our 7kva genset has the sound shield permantly off as I like to see what's going on.
It is on collapsed isoflex type mounts bolted to a steel frame bolted to two layers of 17mm plywood.
Of interest is a 3mm layer of lead sandwiched between the plywood which i assume is knock out some of the vibration.

Noise in the living area, engine room door open, is, according to a decibel app, 60db so normal conversation at 3ft
It only gets used for two hours a day on the rainiest of days so not really an issue for us.

There is some vibration so new generic mounts have been ordered from Greece, believe it or not, for about 1/4 of the cost of getting mounts in Australia.

We have carpet laid over most of the saloon which makes it quieter I think. We don't hear the genset in the pilothouse or in the forward cabin.

NL 5kw with sound shield and underwater exhaust in insulated lazarette. When I start it, I have to look at the oil pressure to know it started. If you sit just on the other side of the bulkhead, you know it’s running. I could isolate the mounts more, but my goal was to be able to run in a crowded anchorage. Goal achieved.

Thanks for the comments. I wish mine was as quiet as some of yours. I played with the iPhone app, and with no genset, ambient noise was 30-40. With genset powered up and working, noise level was 65-70. That was pretty consistent throughout the boat, slightly quieter in cockpit. As little as it is used, I will live with it. Thks again.

I have a 5kw Northern Lights in the engine room, under the salon. Carpeting on the salon sole, soundproofing panels in the engine room overhead. No sound shield, waterlift muffler. I can hear mine running, but it sounds like a sewing machine, very quiet and unobtrusive. As said in earlier posts, maybe upgrade the way your genset is mounted, with different or improved isolation mounts. Vibration that is getting to the hull may be the culprit.

dont feel bad...mine inside is about as loud as a noisy fan...but the PO replaced the enclosure with bubble wrap instread of good sound dapning mayerial. I may fix that this summer.

outside within 20 feet you can hear a hum as loud as busy road noise about a 1/2 mile away.

audible but not annoying in all but a single boat, wilderness anchorage.

There are several things that can be done to reduce noise from a genset.

Most enclosures on small gensets (50Kw and down) have only acoustic foam for insulation on the inside. Replacing this with a vinyl/foam composite will knock a few Db's down. Additional baffling on the inside of the enclosure for the combustion air intake will also reduce noise coming out the air penetration.

A close look at the exhaust system may also be helpful. Be sure none of the exhaust hoses are hard clamped to a bulkhead that abuts accommodation space. Exhaust pulses carry some pretty powerful vibration. A hand on the lift and under it may indicate if putting the lift on isolators might be a good idea. What ghost calls "underwater" exhaust is because he has a gas/water separator. These really reduce exhaust noise by directing all the water under the waterline (hence underwater) and increasing the run length and adding turns to the exhaust run. No splashing at all and quite a bit of exhaust noise reduction. A separator also improves back flood prevention.

Lastly but perhaps the best value, is "secondary" isolation of the entire genset. Some previous posters alluded to this, but proper secondary isolation calls for 4 properly sized isolators under the entire generator in addition to the primary isolators. This may be the biggest bang for the buck as these isolators are usually inexpensive for a small genset. The reduction to structure borne noise is often reduced to the point where you may not feel the gen running at all.

Putting pads and such typically doesn't work and isn't worth the trouble. The fasteners used that bolt through the rubber "short circuit" any isolation, and only accidently would the correct hardness and quantity be correct for good isolation. For isolation, use isolators.

Sound attenuation effectiveness is going vary from one mfg to another as well as the installation. You can try to isolate the offending noise by touching different panels on the gen and other attached components and see if there's any changes. It would better if you can have someone up top listen for changes. Also check the mounting and make sure the mounts haven't collapsed. Look for anything attached to the gen that maybe touching a solid mounted component. Worst case you may need to get a different sound deading material. There's several different varieties. I have seen some very quiet genset's insulated with jute. I also have seen some done with foam with a lead layer sandwiched in the middle that very effective. Direct openings for airflow also transmite a lot of sound. If you make the air turn it will help a lot.

or not care too much once down to accetable levels.

part of that is how much you run the genset...tolerating some noise for an hour or two a day versus 24/7 is a pretty wide gap and how much efgort ypu need to making your genset silent.

what is it all worth in time, effort and expense?

Our Onan was remarkably quiet with little if any vibration or movement when running. It was surveyed at purchase,serviced by at least 3 mechanics in 8 years...then we found the inaccessible generator end engine mount nut was off. A tad noisier,some vibration at start up/close down,all acceptable,and it`s tied down now.

A good bit of droning noise can come from engine air intake. Different brands/models use different types of air intake mufflers to varying levels of success. Installing an air filter/muffler from something like a tractor with similar sized engine can make a huge difference.

I have an 8Kw Onan in the cockpit. It is is a sound box. The exhaust is plumbed through a wet muffler, then ties into the port engine main exhaust Unless you are standing on the exhaust tube, you can't hear it. It does smoke when I start it up.

Some of you may take me to the tool shed, but I am an electric boat. I don't have a n inverter that also charges or solar panels. I need to run my genny when on the hook or at the dock with no shore power and I don't care where.

So if you are in a cove or bay expecting no one to run their generator because it might ruin your ambiance, you will not like having me in the same bay or cove.

I recently bought a 6kw at the boat show on special. I currently have a 20kw which is unnoticeable when running. I plan to install this one in the same fashion, that being with sound down isolator mounts and water lift muffler. They tell me I don’t even need the sound shield but I want it anyway for safety and cosmetic reasons.

LOL, "don’t even need the sound shield." Famous last words, since when is a diesel engine running at 1800 RPM quiet?

cafesport said:

They tell me I don’t even need the sound shield but I want it anyway for safety and cosmetic reasons.

Click to expand...

to me the only reason for a sound shield is sound reduction.

mine and many others are a PIA to deal with to gine a genset a great once overs and maintenance on a daily basis.

too many get lazy and daily checks get left out, me included, losing the sound shield would be great, except for the noise.

That reminds me to get out the iphone tomorrow and take some sound readings on the new generator.