Friday, April 19, 2019

Replacing the generator insulation

As I promised last post, I am writing up the project to re-insulate the generator enclosure here. This post will concern nothing else, so if you have no interest in such matters, feel free to skip it. I will return to the travelogue next post, including a bit of excitement we had while I was typing this. And if you arrived here from a forum link, welcome.

We have a 16kW Northern Lights generator. It came with the boat, and it is well-suited to our needs. It's based on a Shibaura four-cylinder engine, which itself is a knock-off of a Kubota design. We had a Kubota in the bus and so it's all very familiar.

Generator enclosure. The new insulation came with a sick-on nameplate which I adhered next to the Northern Lights logo.

The generator is installed in the engine room, which is itself sound (and thermally) insulated, and so the generator did not really need an enclosure to begin with. Many ER-mounted marine generators have none, and, of course, we have a much bigger, noisier, and hotter engine in that room, namely the main propulsion engine. Nevertheless it came that way, and it does help keep the boat quieter (and cooler) at anchor, and especially if you happen to be working in the engine room. Our laundry center is in there, and the generator needs to be running to use it when we are not at a dock.

Northern Lights used a high-quality dense foam insulation for their sound and thermal damping in these enclosures. It's four layers; a thin foam layer glued to the skin of the enclosure, a flexible plastic layer that makes the whole thing somewhat stiff, a thick foam layer, and finally a "skin" of black vinyl that faces the actual machinery.

Over time the foam layers and skin deteriorate, and almost everyone I know with a Northern Lights of our vintage has suffered with the skin flaking off and then the entire assembly separating from the enclosure, usually by the thin first layer of foam splitting between the enclosure and the heavy plastic layer. I meant to take a photograph of this deterioration, but I was so eager to get the old foam panels off the boat that I threw them away before I got to it.

The OEM foam on the smaller top panel. This one was still intact and I left it in place. You can see that it's proud of the lip by about half an inch, and is a gloss black finish inside.

The first panel to go, unsurprisingly, was the horizontal one above the engine. It landed on the hot engine, which cooked it past "well done", getting sticky goo on the engine and generally making a mess of things. We tried a number of products to glue it back on with no success. Finally I drilled five holes through the enclosure top and ran bolts through the foam and some large fender washers, then used metal tape, which came with the boat and is intended to repair the engine room thermal insulation, to tape the edges of the foam to the edge of the enclosure panel.

That worked, after a fashion, but the tape was constantly letting go and needing adjustment, flakes of black skin continued to rain down on the engine and the rest of the enclosure, and in the fullness of time, the three largest vertical panels also separated in the same way and had to be held in place with tape. Something needed to be done.

Over the course of two major boat shows, I stopped at the Northern Lights booth and spoke to their engineering personnel, and I've also made a couple of phone calls back to Seattle. What I was able to discern was that this was a common problem, it no longer happens because they changed to a different insulation system years ago, and that they have no factory answer for what to do about older units. The options were to purchase a whole new enclosure, or replace the foam myself; no factory replacement part available.

One of the smaller panels after scraping the loose foam with a plastic trowel. Now the real work begins.

A few folks I spoke to with this issue opted for a system that involves epoxying (or welding) what look like nails onto the insides of the enclosure and then pressing new insulation over those nails, securing it with cinch clips. This is exactly the system we have throughout our engine room, where the pointy bits are welded to the walls and ceiling. I can tell you from experience they are sharp, and we went to great lengths to cover, flatten, or dull all the exposed ones after they drew first blood. I did not want this system for the genny enclosure, because not only did I not want to get poked; I also worried that hoses and cables inside the enclosure could inadvertently get pierced, too.

I opted instead for a glue-on solution.  The premier product in the space is from a company called SoundDown, but it is very expensive. I have a suspicion that the original foam in the enclosure was actually a SoundDown product. Fearing that anything I used might well come unstuck, possibly in short order, if I did not get the old foam and adhesive completely off, I opted to find something a bit more reasonable for a first attempt.

I ended up buying a product that is sold primarily as automotive hood liner. It's a 3/4" thick foam product with an adhesive backing and metallic facing. That's only about half as thick as our original insulation, but the price was right at just $120 for the entire project on Amazon Prime, and I reasoned that in the engine room we'd hardly notice the difference.

Solvent-scraping the residue. Plastic razor-blade tool is at right. This is a small section after just the first pass; each section took 3-4 passes to clean and resulted in a mount of old foam and glue.

I knew the key to making this work would be to get all the old foam off and much of the original adhesive as well. We have Goo Gone and Goof Off on board, but my concern with those products was that they would prevent a good bond of the new adhesive. I'd have to be meticulous about the removal of the old adhesive completely, then use copious amounts of acetone to remove the residue of the remover.

After asking around on some online forums, 3M General Purpose Adhesive Cleaner was recommended. A quart of that was just $18 at McDonald's, the very nice local hardware store in Fort Lauderdale. I used an old pump spray bottle to apply it uniformly. I also bought a scraper that had a handle which accepted plastic blades with the same form factor as a razor blade. The blades are color-coded according to hardness, and a number of each type came in the package.

I started with the largest panel, mostly because it was the one where the foam had already completely detached, and because it made sense to cut the largest swath of material first. Before carrying it out of the engine room and onto the aft deck (I did not want to be using solvents in an enclosed space), I first used a wide plastic spackling tool to remove most of the crumbling foam from the panel, vacuuming as I went with the shop vac. That left a thin, uniform coating of foam over the original adhesive.

This was actually the first panel, shown here fully cleaned. It's lying on the roll of new material ready to be cut.

Before I figured out the spray bottle trick, I tried using the tiny pour spout that came with the cleaner to apply it in sections. That just made a mess, so I grabbed an old Simple Green bottle that I had rinsed out as a general sprayer. I resisted starting out this way because I was worried the solvent might dissolve parts of the sprayer, but that fear proved to be unfounded.

It also took me a while, and a lot of paper towels, to figure out that I did not need to wipe the scraper after each swipe, but rather just push the accumulated crud up onto a piece of heavy paper, which was actually some of the peel-away backing from the first piece of insulation. Once I dialed in the amount of solvent to apply, the area I should cover for each section, and the right blade to use with the scraper, I settled into a rhythm and it went pretty smoothly.

I had figured the harder blades (yellow) would be the right ones to use, but they broke easily. It turned out that, even though the surface was flat, the flexible blades for uneven surfaces (blue) worked best. All told I use maybe ten blades for the project. And an area about 10" by 12" was the right size to spray to avoid having the solvent dry before I could get it all.

Here's that panel with the new insulation in place. I used some blue tape before handling it, worried that the adhesive needed time to cure. That was unnecessary.

As I worked my way through the foam and adhesive, it became clear that if I used enough solvent, I could remove all the adhesive down to the metal. But I would need at least another quart, and it would triple or maybe quadruple the amount of time I would spend scraping. Instead I decided to stop when most of the foam was gone, and what adhesive remained was "tacky." I reasoned that tacky residue and fresh adhesive would make a good bond. Any place where I managed, inadvertently, to get down to the paint, I cleaned with acetone before applying the new insulation.

Once I was down to just tacky adhesive, I laid the new insulation down over the panel and used a Sharpie marker to mark off where I needed to cut. I used the edge of the panel itself as a straight-edge to mark the cut line, then used a utility knife to make the initial cut, followed by a pair of sharp scissors to finish it. The resulting edge was not perfectly clean, but acceptable for the purpose.

Here's the big panel with metal edge tape in place. This keeps the foam edge sealed and will also help keep the insulation from peeling away.

I laid the new insulation onto the panel, adhesive-side down, then pulled up one corner and worked the backing paper off. Once the insulation was completely adhered I move it into the saloon where I could finish in air conditioned comfort. Finishing involved cutting lengths of the aforementioned metal tape and taping the edges of the insulation to the gussets on the panel.

The top panel was the hardest. In addition to the glue that the factory used, there was the glue that we had used to try to put it back together. I probably scraped that panel twice as long as the others. Since I already had holes in the panel and all the hardware, I re-installed the through-bolts and fender washers, which ought to help the insulation stay adhered.

This panel, above the engine, was the hardest. The big squiggle was extra glue we had used to try to glue it back together. This is fully cleaned just before installing the new insulation.

In all, I did four panels out of the eight total. Two are on the aft side of the enclosure and I don't really have a good way to get them out, as they are very close to the aft bulkhead of the engine room. Of those, one also has baffles which would complicated the process. One is on the starboard end and is also baffled for generator head cooling vents. It has several smaller pieces of insulation and they are intact, so I left it alone. The two aft panels also have intact insulation. And the smaller top panel, over the generator head, is also still intact. Rather than pull off intact insulation, I decided to leave it be and let it fail on its own. I have enough leftover insulation to do the two smaller panels and the small pieces of the larger panels.

After getting all the panels back on the enclosure and starting up for a test, I am happy to report that neither the noise level nor the heat load is significantly different from stock. Also, the newly insulated panels are much lighter and easier to handle. Only time will tell, of course, if the adhesive will hold. The OEM insulation stayed on for a little over a decade before failing. If we get six or seven years out of this replacement I will consider it a win.


  1. Hi,
    I have a 25 KW Northern Lights Generator with noise enclosure. The top and front panel insulation de-laminated last weekend. I was hoping to re-glue the existing panels. Given your experience, do you think this will work if I follow the process you used?

    1. My experience, as described in the post, is that once the original sound insulation comes off, it can not reliably be glued back on. You will need to replace it.


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