New Install, Northern Lights 5Kw Genset

I bought a NL 5kw Genset, with a sound shield. I'm replaceing a well used 1979 Onan 3kw MDJA. It will go in a different spot in the lazertte because of the larger footprint of the soundshield.

Question. What is the most effective way to mitigate structural noise transmission? The lazertte has a "floor" made up of 3/8" Plywood painted sheets placed on top of a 2"x2" stringer structure. The fiberglass hull is heavily laid up 1981 era fiberglass.

The generator will be placed on a 3/4" plywood base that will be screwed to the plywood floor, which intern will be screwed to the stringers.

Should any thing be placed between the plywood and stringers or plywood basse and plywood floor to reduce noise transferance?

First, the 3/8” plywood is not strong enough to make a base for the genset. I would laminate the 3/4” plywood to it and see if you need more support in between the stringers. Then maybe check with a company like Soundown for flexible mounts to mount the genset to the strengthened deck.

I have this genset, which by the way is a good choice. Mine is mounted on a 2" thick plywood shelf between the inboard stringers, aft of the engines. The shelf is bolted to the stringers with no padding. The genset is attached to the shelf on shock mounts which I believe are NL issue. With this setup, I have no vibration or resonance transferred to the hull. I also don't use a sound shield and things are quieter than the Onan I removed that had a sound shield.

I have an 8 KW Northern Light. Although it has a sound shield I leave the front cover off so I can see things. It is still very quite. Having to do over again I wouldn’t bother with a sound shield. My 2 cents.

"What is the most effective way to mitigate structural noise transmission?"

Mount the noisemaker to a heavy structural board or steel frame on its floating mounts.Noise cover too.

Mount the board or steel frame to the boat on a second set of floating mounts,sized for the combined weight..

Expensive to do with a propulsion engine as a thrust bearing and special shafting is required, BUT not a big job for just a noisemaker.

All the items like fuel lines , exhaust , electric wiring and controls must be extra flexible .

I have a 5kw Northern Lights generator, it’s mounted to 3/4” marine plywood. The generator plus sound shield weight is 400 lbs +- with a small foot print for mounting. The installation was 9 years ago and the mount you see in the photo doesn’t transfer noise. The generator is shock mounted to the stainless steel drain pan for vibration noise transfer elimination. This install has proved to be very quiet.
Note, The black electric cord in the photo is to our 450 watt Extreme bilge heater.

You can get from NL or fabricate yourself a steel mounting plate which also serves as a drip pan. Mount the genset to the "pan" with genset motor mounts. This is how our Westerbeke is setup too. Paint the "pan" white.

I have the 5k NL in my engine room just outboard of the main engine. Drip pan hard mounted to a shelf attached to a stringer and chine board. No soundbox at all. Vibes and noise are very tolerable. In the salon and in the cabins, it is just a pleasant purr. Great for sleeping.

A 3cyl has a minor first order vibe (really a "waddle") that tends not to be offensive. 1, 2 and 4cyl are horrible. On those it is good to mount them on a structure that is itself floating on resilient mounts. I find no such need on the little 3cyl.

You may even find the soundbox to be unnecessary, but you already own it.

Ski in NC said:

I have the 5k NL in my engine room just outboard of the main engine. Drip pan hard mounted to a shelf attached to a stringer and chine board. No soundbox at all. Vibes and noise are very tolerable. In the salon and in the cabins, it is just a pleasant purr. Great for sleeping.

A 3cyl has a minor first order vibe (really a "waddle") that tends not to be offensive. 1, 2 and 4cyl are horrible. On those it is good to mount them on a structure that is itself floating on resilient mounts. I find no such need on the little 3cyl.

You may even find the soundbox to be unnecessary, but you already own it.

Click to expand...

Ski
Excellent point on the 3 vs 4 cylinder vibes. Some years ago we had a 3 cylinder and it was soft mounted in a pan, I thought that was SOP. Other than that all our units have been the rambunctious soft mounted 4 cylinder units that jump around a bit during startup and shutdown.

All diesels with low cylinder count will jump around on startup and shutdown, especially on soft mounts like most gennies. Normal.

The three cyl both ends of the engine wants to rotate a bit, with the front doing it 180deg out from the back. This vibe is 1:1 with engine rpm But add the mass of the rigidly mounted gen end and there really is not much vibe left. With factory soft mounts very little vibe gets into boat structure, and at the low frequency it does not tend to bother anyone.

The four cyl is a different story. It has a second order vibe (often called a buzz) the shakes the engine straight up and down at twice the frequency of crank rotation. It turns out that at 1800rpm this buzz is 60hz, twice that and much more intense than the 3cyl vibe. This is why lots of higher end 4cyl engines have dual balance shafts with weights in oil pan spinning 2x crank speed. I don't think any smallish 4cyl gennies have such.

I can walk onto a boat with gennie running and tell right away if it has 3cyl or 4cyl.

On a four, it is good to mount gennie on a heavy board with a secondary set of isolators between the board and boat structure.

Won't even talk about 1 and 2cyl. The are infernal beasts. Six cyl smooth as silk.

The new NL machines come with a stainless pan and additional plates of stainless welded onto the bottom of pan at the ideal mounting location. I used pulltruded 4” fiberglass tubes to lift the machine of the deck to allow better access since I had the room. The nl rubber isolators between the pan and the generator rails are really all you need. These machines are very quiet. Here are some photos of a 6kw I put in last june.

A couple of questions regarding my 'new to me' NL 5kw 643 NON SERVICE SIDE OF GENSET

The first picture are of two wires coming off off of the wet exhaust port. Do these two wires go to gauges, alarms or shut offs?


On the non service side of the genset there are two wires coming out of a small wire cluster. The pictrue is the one below.
I think these are oil low pressure and high temperature alarms. Is this correct? How and what do you attach them to?

Do any of you have pictures of the how these wires and what these wires should be attatched to?

I will second two things that have been mentioned. What has become more common and is called secondary or double isolation. This is to mount the entire unit including sound shield on a second set of isolators. Generators do not need this, but a second set of isolators work better than just the one set the manufacturer used. It is very important to select the proper size, units with the proper load and deflection specs. For a genset that size you should pay no more than $50 each max.

The structure you mount to needs to be structurally stiff. Isolation mounts, either factory or secondary work better when mounted to a stiff structure. 3/4 ply instead of or in addition to the 3/8 that's there. Are the frames secure to the hull or stringers, if the stringers are tall are the tied together with framing. Stiff is good

If you do use secondary mounting to ply and then isolating the ply to the deck as mentioned is good to reduce noise coming through the drip pan which in not insulated. Mass stops noise, the more "stuff" between you and the noise the quieter.

Keysdisease said:

I will second two things that have been mentioned. What has become more common and is called secondary or double isolation. This is to mount the entire unit including sound shield on a second set of isolators. Generators do not need this, but a second set of isolators work better than just the one set the manufacturer used. It is very important to select the proper size, units with the proper load and deflection specs. For a genset that size you should pay no more than $50 each max.

The structure you mount to needs to be structurally stiff. Isolation mounts, either factory or secondary work better when mounted to a stiff structure. 3/4 ply instead of or in addition to the 3/8 that's there. Are the frames secure to the hull or stringers, if the stringers are tall are the tied together with framing. Stiff is good

If you do use secondary mounting to ply and then isolating the ply to the deck as mentioned is good to reduce noise coming through the drip pan which in not insulated. Mass stops noise, the more "stuff" between you and the noise the quieter.

Click to expand...

So-called double isolation mounting is what I see in fancier boats where a lot of attention has been paid to making it quiet. The NLs that I have seen all have the engine/gen assembly isolation mounted to a bottom frame/drip pan. That makes up one layer of isolation. A quick install is to just bolt that whole thing to something solid and go sailing.


If you want to further mitigate noise, use another set of isolation mounts to attached the gen/pan assembly to the boat structure. That makes up the double isolation.


Then there is a third step you can take, if so inclined, that I have seen on very high end boats. Mount the gen/pan assembly directly to a solid, heavy platform. The heavier the better. Then isolation mount the gen/pan+pad to the boat structure. The platform moves with the gen/pan, and the mass dampens the movement/sound. So the resulting stack-up is:


- Boat structure
- Isolation mount
- Heavy mounting platform
- Gen/pan frame assembly
- Then the pan to engine/gen isolation mounts that are part of the gen set which are factory installed.


I've seen this arrangement called for in engineered sound mitigation schemes.

grahamdouglass said:

The first picture are of two wires coming off off of the wet exhaust port. Do these two wires go to gauges, alarms or shut offs?
View attachment 86872

On the non service side of the genset there are two wires coming out of a small wire cluster. The pictrue is the one below.
I think these are oil low pressure and high temperature alarms. Is this correct? How and what do you attach them to?

Do any of you have pictures of the how these wires and what these wires should be attatched to?

Click to expand...

So this genset came out of another boat?


Get the manual (downloadable from NL web site), and in the back there are wiring diagrams that will tell what all that stuff is and what it should be connected to. I'm not sure why any of it is disconnected.

on Display at the Ft Lauderdale Boat Show

There are two temp instruments up near the front of the manifold and circ pump. One is temp trip, one for a gauge (if used). Kind of hard to get to, and why the heck were leads disconnected?? The exhaust has a temp trip switch, one lead goes to ground, one into the trip circuit. Trips if circuit closes. Need to consult schematic to figure what goes where.

On our new NL 9kw Genset we went with external NL iso mount extra and sound shield. Unit bolted to 1 inch marine ply. Very happy very quiet. Professionally installed with magnum 2812 inverter charger.

Soundown also make a lot of mounts etc but you might find your exhaust set up transmits more noise out of the sound shield than the mounts.

We have the same unit. Roughly 2k hours.

Put the SS manifold on it.
I made a new pan and raised the motor mounts 1/2 to clean under. Should have done it 1". It is 1/8" plate steel. If you make one put a drain and ball valve in the pan.
We have no sound sheild, it does not need it

On our GB they mounted the NL gauges in the engine room, next to the genset. I moved them to the helm and extended the harness.

Turned voltage up to 130v.
Replaced control box isolators.
Added manual oil drain pump.
Replaced air filter, it can easily eat it.

Ours had Japanese fuses, impossible to find and very expensive, and two spares in control box. Bought a box of ten from Fuseco in Houston, around $8@ if I remember correctly. They ride in the control box.

Wish it had frequency gauge.

Nice unit.

We change the oil when we do the main engine, sometimes at 20 hours.

Plumb oil discharge to auto oil change unit so you can do engines and Genset easily.