Sound Proofing the engine room

The engine room received one more coating of paint on the hull and sole framing last weekend in preparation for starting the sound proofing. Well, I hope its sound proofing, as it will be a real pain in the ass to re do this once the boat is launched.

My system for sound proofing is pretty basic. I foamed the metal ( see the last post), and now Im attaching a 1" thick mineral wool board the the framing. Over this mineral wool Ill attach a perforated aluminum sheet as my finished wall material.

As best as Ive learned, the idea behind sound dampening is to decouple the structure from the sound. Sound travels in waves and the idea behind getting rid of it is to try to absorb it. My system is to provide a barrier between the living spaces and the engine room noise. My thoughts are that the sound will pass through the perforated aluminum then be absorbed by the mineral wool board and also by the foam underneath.

The mineral wool Im getting is discarded seconds that came out of a large sheet metal fabrication shop. Id love to have 3 x 5 boards, but Im only able to get 2x4 boards ( the price is right though). Because Im not able to pick my size, Im having to adjust my framing. In the areas I know Im going to have to attache lots of conduits, or other mechanical items, Im first installing plywood before installing the rock wool board. With the plywood on the hull framing ( 1/2" ply ), I dont have to worry about the rock wool laying out to hit the framing so there is almost no waste of the rock wool. I also have unlimited points of attachment for my future mechanical installations. For the ceiling though, Im going to have to add a firing strip so the rock wool waste is minimized while I keep an eye on the weight Im adding.

Ive got a little of the product up and on the walls and part of the ceiling. Im working in the corner where the generator will be installed, and Im amazed at how well the sound seems to be vanishing from just having that small area installed. Its no longer necessary to wear ear plugs while working in the hull. The only drawback is that the engine room is starting to get hot from the heat from the lights.

The perforated aluminum looks fantastic and gives me just the gear head look I want for my engine room. Once the material is screwed to the wall, it stiffens up nicely. You have to look closely to see the rock wool underneath, so I feel good about the ability of the perforations to contain the rock wool while also letting the sound waves into the dampening zone. The open area of the perforated sheathing is 34%. I picked up some advice from the good posters at Metalboatbuilding.org on how the cut the stuff. Its so nice to be able to start seeing some finishing material finally going on.

Because the rock wool is 1" thick Im going to have to fabricate some corner pieces or trim some areas out with aluminum angle. One of these areas is by the doors as you can see from this picture. Im leaning towards angle in some areas, while in other areas, Im going to try to brake ( bend a corner) the material in to an outside or inside corner.

I took a crack at bending some material into a corner, and it worked out OK. Having corner pieces makes the job look much more finished and I dont have to be as particular on the fit.














I had to add firing strips to the main area of the engine room ceiling. While I hate to loose another 3/4" of head room, Im willing to take the trade as this allows my rock wool to go up with less waste. The frames for the boat are 30" on center, and my rock wool sheets are 24" x 48". I dont have the choice of 3 x 5 sheets so I added the firing strip to make things work better and get the most bang for my buck in regard to how much rock wool I have to buy.

I started out cutting the perforated aluminum with snips, but Ive now switched over to my table saw. I added a board to the saws fence so the 16 gauge material will not slide under the fence. The table saw does an excellent job of cutting the material and it looks like it was done on a shear.

You might have noticed I have some plywood installed under the rock wool. I have plywood over the fuel tanks to protect the paint job on the tank and also to give me a way to easily attach engine room components to the tanks. I plan for some cabinetry and shelving, among other things, to be installed on top of the tanks. The forward and aft water tight bulkheads also received 1/2" plywood. I installed plywood on the aft bulkhead due to the idea that my generator will sit on the starboard side, and my fuel transfer/polish manifolds and pumps will be on the port side. I dont know the exact layout of any of these components, so I put the plywood up to make it easier to attach the various bits and pieces of each system. I went with plywood on the forward bulkhead as this is the area where my work bench will be, and I want dont want to be limited to the bulkhead framing as the only points of attachment for various things.

I cut it a little close on my measurements for my fuel tank fill points. I wanted the fill lines to be as close to the outside hull sides as possible, and as you can see I achieved that. I had to hog out a bit of the rock wool, then push the aluminum in to get the two inch nipple to thread in. The rest of the assembly will fit just fine as the hull is leaning outboard at this area of the boat.

Im pretty happy how the material bends and the fact that Im able to fabricate some of the corner pieces I need. This picture is where the ceiling jumps up to accommodate my door. This detail is the same on both the forward and aft sections of the engine room. This detail also gives me three more inches of headroom over my work bench.

The room is about 70% complete in regard to fitting out the aluminum wall and ceiling sheathing, and 100% finished regarding the sole, so I decide to drop in the generator. The engine room is now completely closed off. Im going to miss that large opening as it was easy to drop material into the space, and it also made things nice in regard to ventilation.

The engine room, for the most part, is sheathed. I still have to cover the seams with some trim, but Ive yet to find a source or figured out what the trim will look like. Im thinking I"ll go with a 1" piece with some sort of slight brake on both edges.

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Engine room sole

The engine room sole is sheathed with 1/4" aluminum diamond plate.

I was planning on using plywood for the sole due to cost concerns on my part, but having found this plate at the scrap yard has allowed me to go with, what I consider, a more attractive sole. Because of being in the engine room, and also I believe it could be a common event to have to lift pieces of the sole off for maintenance I bolted wood firing to my steel framing and then attach the aluminum sheathing to the wood. If I had screwed the aluminum sheathing directly to the steel I had visions in the not to distant future of broken screws, corrosion where screws penetrated the steel, and just more difficult maintenance in general. Having wood to screw the aluminum in to will also give me a little vibration dampening in my opinion. Im using #12 x 1.50" stainless steel wood screws that Im countersinking as my fastener. The sole is complete as I write this post, and to date, Ive used 150 of the stainless screws to fasten the aluminum down.

I wanted as much level area in the engine room as I could build, so I stepped the sole framing up as the sole moves aft in the engine room. These steps, while some might not like, give me places of access underneath the sole, and also give me a place to sit while Im in the engine room. Whenever I give friends tours of the progress, almost everyone sits on one of these steps. This picture to the left shows the platform I built for my tool box, and my hydraulic system reservoir.

I think the largest piece of material Ive used for the engine room sole is a finished cut piece of 24"x 24". I dont want to be having to man handle large pieces when Im I have to access under the sole. I would rather be able to lift smaller pieces, to gain access and still be kneeling or sitting on the level sole. The down side to having all these smaller pieces is I used quite a few screws.

Im getting a pretty good feel on how the engine room is going to layout and I think Ive found locations for the various equipment Im going to need. Im going to dedicate the port side of the room up against the main bulkhead at frame #9 as my area for my work bench. While the head room is around 5"4" in this area, Ill be able to use a short stool with a lower work bench to be able to work in a comfortable position. Ill post more about the engine room as a whole once I begin to install the various components.

The last piece of the sole for me to build is the area over the stuffing box. Im almost out of aluminum plate so I have to give it some thought on how I want to treat this area so I dont waste any material. I think Im going to hinge a part of this area so I can gain quick access to the stuffing box for maintenance, daily checks for leaks, and stuffing box temperature.

I have 4 10" of head room on the starboard side of the engine, and 5 2" on the port side of the engine. I have more headroom on the port side by my design as I knew this area would house my work bench. Id love to have a stand up engine room, but on a boat my size, I think that would be almost impossible. I think once you get into the 50 range, stand up engine rooms start to appear. Im totally happy with the size of the engine room, and very pleased with the head room I do have. Ill be able to easily do all my maintenance work in this space in comfort.

The scrap yard aluminum worked out great. There are some blemishes, and some cleaning that will have to be done. I know as construction progresses, the dings I put in the sole, will blend in to what was there. Ill probably never do much more than clean up the messs I make. I have to say that I love the way the engine room is shaping up.

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Scrap yard finds for the engine room

My excavating business is as poor as Ive ever seen having been self employed for 20+ years. With my revenue down so low and my not wanting to not work on the boat even though I have much less cash to throw at the project, Ive taken to visiting scrap yards looking for some material.

This post still reflects my working in the engine room, but I want to look at the value of utilizing used material.

Given the down turn in the economy, I had my mind set that I was going to have to sheath the engine room floor in plywood and probably paint it. While down at the scrap yard today unloading the fruits of me cleaning up around the shop, I noticed some aluminum diamond plate getting ready to be processed. The material was a double diamond plate pattern 3.5 x 7.5 x 1/4" thickness. There were 20 sheets, but from what I could remember five sheets would be plenty, so I went ahead and struck a deal for six sheets. We agreed on a price of $.80 per pound. For the six sheets my total costs were $300.00. The pattern of the diamond plate was nothing Id ever seen before, and as you can see from this picture, it is a double diamond pattern. From here on out, Im going to call it "Double D", or "DD". Personally, I am partial to "DD", and it just makes me happy thinking about it.

I also needed a 2" stainless ball valve for my sea chest, and a 1.5" stainless ball valve for my holding tank pump out station. This scrap yard had a large bin of stainless valves and it only took me a couple of minutes to find two I thought looked good. I paid $1.00 per pound for the valves so my total cost for the valves came to $18.00. Both valves were 316 grade.

Once back at the shop I took the valves apart, applied some lithium grease, re-assembled them, then air tested them to 40 psi. I only used 40 psi since I was using PVC for my air test, and in all honesty, the valves will see no more than a two or three psi of pressure.

I also made a call to my local metal supplier to see what the costs were on new 1/4" diamond plate aluminum sheets. I was quoted a price of $3.75 per pound. The sheets of diamond plate I purchased weighed around 375 lbs. With the new cost of $3.75 I figured I got $1400.00 worth of diamond plate for $300.00. Im also going to estimate the value of the valves @ $175.00 and $150.00 respectively, for a total valve value of $325.00. By purchasing used material, I think I can figure the new value of the material at about $1700.00, but my total outlay for this material was only $318.00. Quite a nice savings in my opinion. I should also say that the scrap yard paid me $249.00 for the 2700 lbs of scrap I dropped off.

One more thing I should add about the valves is that they are rated at 1000 psi, and I think they are sch. 80 or sch. 120. I can say with confidence that these valves are what I would call "beefy" valves, and have what I would guess double the duty rating as any valve one might buy from a marine catalog.

The aluminum diamond plate I purchased was obviously used as a cat walk or some other industrial application. This is a great example of why metal is such a good building material. While this material could have been in heavy service for 20+ years, a little work on my part and it will clean up and look just like new. I also think that the aluminum diamond plate will make my engine room floor as fine as any of the so called high end production plastic yachts on the market.

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