Main engine sound enclosure

With an engine on classic engine mounts, taking tons of thrust it is simply impossible to reach that level of soundproofing.
OK, but.....
I think you'll find that a lot of the big boats with big power being built these days have soft mounts and flexible couplings with thrust bearings. Very little vibration being transferred to the engine beds, stringers and hull. The engines are not in boxes but the entire engine room is sound insulated to the max.

Soundproofing of engine rooms is now normal and it works - no argument about that. My problem remains: in a 46' motor yacht the only place I can put the workbench is the engine room; and there's a lot of ancillary equipment in there that will need maintenance. I just don't want to have to suffer the main engine noise when I'm in there. So I guess I'll keep studying this and see where it takes me.

 

I happen to be one of the quiet boat people.and boxed in my engines years ago.
There happened to be handy areas to mount angle aluminum,and I was never trying to cover every last single hole.
Just trying to cut it down.
A few wing nuts,and the panels are off.

With lots of engine room sound deadener, and other than the very low frequency stuff and exhaust I can sneak up pretty close on ocean kayakers.

Been wondering about an off phase sound cancellation system with a few speakers mounted down there.

 

@WestVanHan
Phew! I often think with my wacky ideas that I am the only one thinking outside (in this case inside) the box. So it's great to find someone else thinking the same way.

How quiet is it in your engine room/compartment when the mains are running? Could you work in there if you had to?

 

That is a good solution if you are satisfied with a single quiet spot. It is impossible to maintain 180 degrees phase shift in the whole room.
Also, the amplifier and speaker system must be able to produce the same noise level as the source of the sound you want to suppress.

 

To remove thrust transmitted noise you use a thrust bearing. Very common on yachts.

Working in the engine room while the machinery is running is never quite...ear protection is the solution.

 

Just how much time do you plan to spend in the engine room with the engines running Boathome? Is it so much time that enclosing the engines is really a good idea?

Like Michael said:

 

I would never work in the engine room when the main engine is running. When the gen is running, its not bad. Earphones are the way to go even though my gen is boxed and reasonably quite.

 

Just how much time do you plan to spend in the engine room with the engines running
Depends on the length of the passage. Lymington to Bembridge = nil time in engine room (I hope). Azores to Bermuda - who knows? Depends what breaks. In there will be all the pumps, most of the Maretron sensors, the fuel-polishing... you know, all that stuff. And the workbench. I mean, the hair dryer might need fixing.

I would never work in the engine room when the main engine is running
Exactly. The conventional approach makes the engine room a "no go" area when under way. Earphones help of course, but reducing the noise is the way to go.

I vote for WestVanHan's approach.

 

I go down fairly often to have a listen and inspect,but never while at speed.
It's a lot quieter with the panels up than down.

That's right,and amplifiers and speakers are cheap-put in as many as needed.

I just like very quiet boats. On the bridge at low speeds all I hear is wind,some waves,and a faint low frequency rumble.

 

I bought a pair of nose cancelling headphones for flying. Very cheap (USD15) but they make an amazing difference. I wear them the whole flight (up to 10 hours) so are comfortable enough and quiet even when I don't play music through them.

I assume they are specifically designed to cancel jet engine noise rather than low Hz diesel engine noise so may not be so effective in an engine room. But presumably they can be tuned to suit specific frequencies.

I also like quiet boats - that's why I sail!!

Richard Woods

 

sound reducing engine box

About 1983,I designed and built a little 20' motorsailer based on an older hull of mine the TS18 and I mounted the 15 hp Yanmar inside a 4" thick glass foam box with lead sheet on the inside. I hate noise and this box did the trick. The top of the box was molded into steps to make it easier to get from the center cockpit to the wheel house. I tried to capture the essence of the Fisher motorsailers with the design except that I wanted to be able to sail w/o the wheelhouse in the way-hence the center self draining cockpit. Inside the little wheel house you could still hear and feel the engine but it was much quieter that w/o the box.

 

Smaller boxed in, insulated propulsion cabinets are very common in many smaller boats, 22- 30 foot inboard outboards that do not have the available space for a larger engine room.

There are hundreds, if not thousands of inboard jet drives running around, of which we have built many, that use this concept in aluminum boats which are prone to vibration transmission.

In many cases the occupants are within a few feet of 400 horsepower gas engines running at speed

Some aspects for our solution

The sides were built out of 1/8 inch aluminum then we glued in an 1 1/2 inch of a mylar faced, acoustic foam that had a dense decoupling layer about 1/4 of the way through. They were bolted together and had a 1/4 inch foam weather stripping glued at the flanged.

The top, because it was part of the inside of the boat, would be out of 1/2 inch ply bolted to the side panels, with the same acoustic foam glued on and we also upholstered the top to sit on.

The real problem came from the ventilation and the bilge area.

We took 4 inch flexible ducting into an area close to the engine boxed area, from about 8 inches above the floor but facing rearward. We would install a similar sized rigid pipe about 24 inches long somewhere along this length and hooked to the flex, and pack this with a stainless pot scrubbers, high tech, bought them from a grocery store as we could not find this commercially though it probably exists. The pot scrubbers looked like a mesh and when installed into the pipe, acted as a muffler for the noise that would come out of the ventilation intake.
(we often built our exhaust mufflers along the same line width some other mods)

The real problem came from surrounding the lower part of the engine. Between the stringers, we would bold in an aluminum min bulkhead with an upper flange that match the front of the upper box sides. Then glue on more acoustic foam.
We made accommodations as we only had bilge pumps at the rear of the boat, by taking 1 1/2 inch pipe, packing them with the same stainless mesh and tacking them into the floor to provide a water egress from the front to the back bilge pumps.

Normally the top would be on a hinge to make checking oil etc easy and it was only if there was some serious work that had to be done, that we had to unbolt the sides or front of the engine cover.

The most important parameter is that to really work well, the engine has to be encased as if there is even a few square inches of the noise to get out of the engine compartment it will and negate a lot of the work.

As an experiment, turn a stereo on in an adjacent room, close the door and stick a towel to seal the bottom.
1) remove the towel, the sound level might raise 20%,
2) open the door an inch. the sound level might raise another 20%

You might have an exhaust pipe issue if the exhaust is not wet and cool, and of course the prop shaft problem, which we did not have as we used the transom as our sternward side of the engine box

 

Working for a manufacturer, I can give you some perspective from our point of view as to "Why Not?"

1. Size. The engines we manufacture are installed on everything from RHIBs to Yachts and everything in between. On smaller vessels especially, an enclosure just increases the amount of space required, provides little extra soundproofing, and can get in the way of installation and, more importantly, ventilation. We tend to make the model that will fit in the most applications. Anything outside of that norm would be considered optional or bespoke.

2. Impeded access for maintenance. On said vessels with engine compartments instead of an engine room, an enclosure can easily block access when servicing the engines. On MANY installations, we are asked to provide remote starter motors, filters, and even move the intercooler. Some brands (Steyr pops into my head... Not a competitor, so do not read anything into this) of engine were designed with enclosures and protrusions that are appropriate for other types of vehicle that are difficult to access even without a compartment. (Steyr was in armored vehicles).

3. Heat is the number 2 mechanical issue with our engines (after bad fuel). Enclosures can act like a heat sink and make cooling more difficult. Think about where gensets are normally used. Mostly, in areas with more air flow and access.

4. Cost. Any enclosure will add to the cost of an engine. Margins on engines are extremely thin (we make our money, as do most manufacturers, from spares, service, and training). Cost is always part of the picture, and unless customer demand covers the cost, it is left out.

5. Customer demand. The situation you described is the first I have heard. Not saying others would not want it, and if I had a few hundred people ask me for enclosures, it might be considered viable enough to try and sell an enclosed engine, but as of now, probably not (for us). We would actually, if a customer requested an enclosure, probably refer it to one of our distributors for local fabrication.

6. Engine rooms and compartments are typically soundproofed or insulated anyway. Little additional benefit. On sound-sensitive installations, usually military with us, the concern is engine noise outside of the vessel, in most cases, and that is handled via other means (usually mounts, vibration reduction, silencing, and insulation).

 

@jmiele - Thanks for your very helpful reply.

If it wasn't for the fact that I expect to spend time in the engine room under way I wouldn't bother with a sound enclosure for the engine for exactly the reasons you (and some of the other replies) have given. If the engine room is an uninhabited area it makes sense to soundproof the whole room and not worry about the noise inside it. But as I said above my engine room is where most of my pumps etc., and my workshop, will be. Having tweaked my design to give myself 1.8m headroom and plenty of working space I don't want to be excluded by noise. I know all about ear muffs - I hate them. My idea is to enclose the engine and the engine room.

The thing that I can't get my head round is cooling. This crops up all the time - here for example: 'We also ran a bunch of tests to check the engine room temp relative to Deere's specs. On earlier sea trials it seems much hotter than expected, so the boat had been rigged with gauges and we were tasked with producing a lab report. Sure enough, the temps were too hot and drew Jeff Leishman down to the dock on our return who in about 5 minutes spotted the problem. The wrong fan had been used when the boat was built. Once corrected, things looked much better.

My take on this is that the cooling system for the engine - whether keel cooled with a dry stack like the boat described above, or wet exhaust - should be designed to keep the engine temperature where it needs to be. I don't understand why in larger boats it often doesn't achieve this and you have to cool the engine room as well with fans drawing in air, circulating it, and expelling it, all of which uses energy. Is this because you can't cool an engine with a water system, or is it that the heat exchangers and pumps aren't big enough?

 

Much of the noise transmitted to the hull from the engine is mechanical,not air born.

The Gov boats for monitoring fisheries etc (unlimited budget) frequently will mount the engine drive package on a frame that is suspended on its own isolation mounts.

This required great flexibility in the shaft hookup and all piping and wiring.

They claim it works well (at one or 2 speeds) to not scare the little fishies , so they can be counted.


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""Is this because you can't cool an engine with a water system, or is it that the heat exchangers and pumps aren't big enough?""

Engines require to be at an operating temperature to be efficient 180-200F is common.
Cooling the engine tranny and exhaust to outside air temperature could be done but the engine would have a hard time surviving

Squirrel cage blowers are efficient and quiet in operation.Not a big power cost esp compared to a room temperature engine.