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bcooke wrote:I am looking into insulation for the engine room (engine box really)
Nothing but the best of course. But what is the best?
The point is to reduce cabin noise and heat.
-Britton
Britton,
I can't tell you which product is the best, but I can offer my own experience with a material that looks similar to your first option.
I used a 1" open-cell foam with an inner PVC vinyl sheet, and I've been very happy with it. It has drastically quieted the 4108 Perkins and, I'm sure, reduced the amount of heat that finds its way into the cabin. If you do go this route, one thing I wish I'd done was to seal off the ends where the foam is exposed. It seems inevitable that some water finds its way to the foam, whether when topping off the header tank or changing the impellor.
Very nice David. Why use "open cell" foam? Does it have better insulating properties?
This is one of my "someday" projects as well, so I'll be following with interest. At some point I read about someone who installed "tiles" that could be cut to size and were sticky on one side. I forget the product and where I read it - sorry.
So 1" should be enough and the "more is better" and "price is no object" arguments can be safely left behind?
Nice story about the squirrel Tim!
One of the two products from Hamilton's catalogue is lead lined. Probably the same stuff Tim used.
I may postpone the purchase of the insulation but the box can be built and I want to make sure I leave adequate clearances. On the other hand $100 worth of material seems pretty good if the stuff works well.
-Britton
-Britton
Work is overrated.
Most everything you read on the Internet is wrong.
You can get a few decibels out of thickening the plywood around the box too. The foam works to absorb the sound, and the lead helps a little with isolation via dampening... But if the whole assembly "breaths" the outside of the box is a giant speaker cone. 6db reduction for every time the mass of the panel is doubled.
The mass law is most effective at low frequencies, the ones that move things and make the boat shake. (Double the mass of the boat and it shakes less? <Big Grin>)
If the material can't flex, it is hard to vibrate... what doesn't vibrate doesn't transmit sound. The higher the mass for the same unit, the less it transmits. Lead is good, concrete is good... styrene foam board is bad. Thin materials can have dampening pads placed on them, much like laying your hand on a drum to provide mass, which dampens the vibrations. A wide panel with 10% covered with something that increases its mass, dampens the the sound which it transmits. On a sheet metal, asphalt tiles work wonders, but just doubling the thickness, even if only in the middle of the panel helps too.
One of the coolest installations of sound deadener I've seen involved Masonite tile board and lead sheet... with one of the stupidest dry exhausts ever. The shower on the other side of the wall, and one could take a shower without getting their ears boxed in... even with pipes emptying directly below a pair of massive mufflers... but were not physically connected. The thought was the exhaust would suck air out of the engine room on its way out the stacks, and provide negative pressure to the engine room to pull in fresh air at the back of the boat. (The helm was situated at the front of a rounded cabinhouse. At 1,350 RPM it'd darn near box your ears in, as the "Sweet spot" was about ear level! Ripped out the dry exhaust and went wet just because of that...)
On a lot of boats the engine has open access to the bilge, and the bilge is set up to breathe fairly well to the rest of the boat. Installing a bulkhead that goes all the way to the keel with just a limber hole quiets down the transmission to the rest of the boat. As does connecting the engine stringers to the deck, so if the engine wants to vibrate and bounce around, it has to vibrate the whole boat. Otherwise it vibrates all the interior joinery, and anything not nailed down turns into a speaker.
If you really want to geek out, set a pan of water on the sole and go run around under power. Find the RPM where the water in the pan dances, and that is the RPM which the boat/engine and Prop harmonize and start singing together. You want to make sure that your cruise speed does not coincide with this, as it is the point which everything vibrates the worst. The propeller is one that is hard to see, but if you've ever been on board a boat and stood on top of the shaft log, or strut and gone through the powerband props have an RPM which they don't like to run. The shaft, strut and everything else bounce around. On a flat bottom boat in shallow water you'll actually feel the back of the boat vibrate and bounce around in extremely quick sequences, sort of like laying over the fender of a car running on half its cylinders.
(Yeah, I get way to much enjoyment out of decibel meters, and the pursuit of reduced noise in machinery...)
I am not going to go too crazy with this. My A4 doesn't make that much noise after all. I hadn't known about the thickness of the engine box panels. I was planning on light 1/4" panels but I could easily beef them up to 3/4" without leaving my scrap pile. Good tip.
So no one thinks I should put two layers of 1" insulation then? Good. Mostly, I need to build the box so I need to factor in my clearances with the insulation in place.
On a lot of boats the engine has open access to the bilge, and the bilge is set up to breathe fairly well to the rest of the boat.
Yep, like my boat. There is about a 3 foot drop below the engine with my bilge pumps and hoses that would complicate a bulkhead. (Access issues). Maybe I can build my proposed engine pan with some sound deadening built into it. That is something to think about... next year.
If you really want to geek out, set a pan of water on the sole...
Thanks, but no. I am already crazy and I don't feel the need to express it in any new ways :-)
-Britton
Work is overrated.
Most everything you read on the Internet is wrong.
Britton,
One thing to add to Zach's excellent post.
The more airtight you get the box, the better it'll be at soundproofing the engine. Just a small opening will allow a surprising about of sound to escape. Sound is essentially just moving air. If you don't allow anywhere for the air to go, then you're far ahead of the game.
Thanks. I was thinking of making one box rather than a series of interlocking panels like in the original setup. I thought it might reduce rattle but your idea suggests it might keep sound from escaping from the loose corners.
Considering the location of the engine in the boat I think there is only so much I can do with it. These suggestions are going to help though. Luckily my smooth, quiet, sewing-machine-like Atomic Four is not like those nasty, rattle-y loud, smoky diesels... :-)
-Britton
-Britton
Work is overrated.
Most everything you read on the Internet is wrong.
