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Old 07-09-2018, 09:19 AM   #1
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Cabin noise

I know it is subjective, but what is everyone's opinion on the level of cabin noise from a single vs twin? Is there a significant difference?
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Old 07-09-2018, 09:55 AM   #2
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At anchor a go fast with bikini twins and a single guy is quite nicely noisy.
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Old 07-09-2018, 12:01 PM   #3
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Not really my demographic, but okay then!
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Old 07-09-2018, 12:42 PM   #4
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Were you interested, here is a site for free apps for sound level. I have one on my phone and with a single in a 28 foot trawler, we register 71-72 decibels at 1600 RPM and 68 at 1450 RPM. (6.7 knt. vs: 6.2 knt) guess where I set the throttle!! (Sometimes in rare conditions, the boat wanders into 7 knots. where the oxygen mask drop from the overhead.!)

5 Free Noise Meter iPhone Apps To Measure Level Of Noise Around You
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Old 07-09-2018, 12:57 PM   #5
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Were you interested, here is a site for free apps for sound level. I have one on my phone and with a single in a 28 foot trawler, we register 71-72 decibels at 1600 RPM and 68 at 1450 RPM.
I started a soundproofing project on my engine room and I can tell that microphones on modern Android phones (tried Google Pixel 2 and Galaxy 7) are too "smart" and dramatically reduce the reported noise level after ~70db.

Better get a $20 dedicated meter from Amazon.

To original poster: Given all the other parameters are the same (engine manufacturer, engine mounts, RPM, etc) the twin will be quieter, but by very little. If you want to lower cabin noise - make sure you have modern shock absorbing engine mounts and cover engine room with 1-2 inch neoprene + mass loaded vinyl sandwich.

Here is a quick intro to marine soundproofing
http://www.soundown.com/Section%203%20PDFs/Handbook.pdf
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Old 07-09-2018, 11:06 PM   #6
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For us smaller boats, one can obtain from NAPA or similar auto stores, rolls of quilted sound material. I believe a roll runs about $50.00. Below is the product that I applied. There are superior products but were not available. I doubled up on this applying on the underfloor of the engine compartment and the under floor of the engine hatch. Easy to cut and staple or as I did, used the nails with round green plastic washers. (Sheet Rock nails?)





Car Insulation - 4' x 10' Roll (40 Sqft) Sound Deadener & Heat Barrier Mat - Automotive Lightweight Thermal Insulation
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Carinsulation.com
Car Insulation - 4' x 10' Roll (40 Sqft) Sound Deadener & Heat Barrier Mat - Automotive Lightweight Thermal Insulation
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Old 07-10-2018, 12:46 AM   #7
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For us smaller boats, one can obtain from NAPA or similar auto stores, rolls of quilted sound material.

Car Insulation - 4' x 10' Roll (40 Sqft) Sound Deadener & Heat Barrier Mat
This will not block the diesel engine noise. "Sound Deadener" is the material to stop vibration of thin metal panels. It is a sandwich of butyl and aluminum foil (it is ~1/8 inch thick). You may need a few square feet to block vibrations of the cabinets, stove parts and tops of the fuel tanks (if they are metal) but it is almost useless for blocking the low frequencies of the diesel engine noise.

To block low frequencies you need materials called "Sound Barrier", which is a sheet of very heavy and non-vibrating material (lead or mass loaded vinyl aka MLV) decoupled from the hull via 1-2 inch thick layer of foam. For engine room you want high durability foam (neoprene) + cover with maylar-based fire blanket.

For lazarette polyethylene or polyuerethane foam would be fine, just cover it with maylar foil or maylar-based insulation bubble wrap, so you do not have to clean degraded foam pieces in a few years.
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Old 07-11-2018, 10:26 AM   #8
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Definitely more noise from twins. 😀
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Old 07-11-2018, 11:06 AM   #9
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Hmmmm...one person on here says slightly less noise, one says definitely more.
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Old 07-11-2018, 12:02 PM   #10
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We have twins and I find while underway the most annoying sound comes from RPM resonance (the whaawawawa between two engines). Without a synchronizer I spend a fair amount of time getting the throttles just right once up to cruise speed. When I do, at the right cruise RPM, noise is very reasonable in the pilothouse, noisier in the salon and "sleep-able" in the staterooms.

I have been considering upgrading the original (cork perforated ceiling tile?) soundproofing to something more modern but that is way down on my list of boat buck projects.

PS - the boat produces the most noise at idle in neutral but that some from a lot of secondary vibration.
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Old 07-11-2018, 12:14 PM   #11
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When refurbishing our boat we used 'Quietlife' sound insulation from ASAP Supplies in UK. Highly recommended.
As part of the silencing programme we also fitted a remotely mounted paper element air cleaner to reduce air intake noise and give better engine protection.
Despite having a flexible coupling we also checked and fine tuned engine alignment.
Altogether a massive difference.
Check asapsupplies.co.uk website, they may have a supplier closer to you.
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Old 07-11-2018, 01:04 PM   #12
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[QUOTE=sanychsamara;679875]This will not block the diesel engine noise. "Sound Deadener" is the material to stop vibration of thin metal panels. It is a sandwich of butyl and aluminum foil (it is ~1/8 inch thick). You may need a few square feet to block vibrations of the cabinets, stove parts and tops of the fuel tanks (if they are metal) but it is almost useless for blocking the low frequencies of the diesel engine noise. End Quote:

Hummmm, brazzen comment. Save to say from a distance of a boat that has the product installed and would be available for personal determinations.

For what reason other than offering a personally known solution to the forum, would I proffer something than had no benefit? The offering was made knowing that there are many sound material available at what cost?

Many of us smaller and most likely, lesser amounts of cash to spend, are looking for economical solutions. This was one. In any event, sir, the boat, my boat, is noticeably quieter for having installed this product.

Regards, Al
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Old 07-11-2018, 02:09 PM   #13
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Definitely more noise from twins. 😀
Itís a question of where the noise comes from.
One would think itís a question of work being done. I had a diesel Nissan Maxima in the 90ís and it was strange re the engine noise. The more throttle on the less noise. I hated the racket that engine made. Isuspect some Albin 25ís had that engine w the Chrysler brand label. With the Nissan car I couldhardly wait to go up a hill .. so I could put a load on the engine and reduce the noise level by at least 1/2. Drove a Cummins powered truck w a turbo and it seemed more dependant for noise. In a powerhouse w a 1400hp turbo Enterprise it seemed more load sensitive for noise. Somewhat quiet at 1/4 load. It was diesel-electric and it went to full power when the operator flicked the switch for high pressure water pumps down on the dredge. Instantly it was extremely noisy. So that engine was very noisy at full bore while the Nissan car engine was quieter under load.

So it may depend on the boat and the engines. And it may be quite dependant on the type of engine and even the fuel injection system.

With a twin you often get the harmonic or beat frequency between the two engines unless they are perfectly synced. If I had to bet on this Iíd put my money on the twin for making the most noise.

But much or (depending on the boat structure) even possibly most of the noise you hear is not coming from the engine .. directly. Quite likely over half the noise is coming from bulkheads, rooftops, hull bottoms and other places where flatish surfaces can ďoil caní continuously. Thatís how a drum works. A membrane moving back and forth. In your boat there are hull and cabin surfaces. Ever ridden in an old ferryboat? Most of them had windows that rattled a lot. All of this kind of noise is like being inside a drum. But noise coming from these sources are indirect and the twin engined boat would probably make about equal noise coming from these sources. And if the boat was going at the same speed as another the same work is being done and should produce the same noise. So combustion noise should be basically the same. But valve lifter, rocker arms and such are pure mechanical noises and the twin will have much more of course. Perhaps up to nearly double the noise.

Obviously thereís a lot of variables and the noise level quite likely vary quite a lot boat to boat and re the engines themselves.
But many here have spent time in both singles and twins and the likelihood of the two (or more) boats being powered by the same engine (FL of course) is very high. So a consensus should emerge after a dozen or so posts.
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Old 07-11-2018, 02:28 PM   #14
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Previous boats were ECs with twins running at 75 percent load and minimal insulation. My ears were literally ringing after a long trip. I much prefer the 1200 rpm single in a well insulated ER these days. Slow, and quiet is nice.
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Old 07-11-2018, 04:56 PM   #15
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Try this. Twin engine boat of your choice, running at any rpm of your choice. Shut one engine down and turn off the key. Does it get louder or quieter?
I'm going with quieter.
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Old 07-11-2018, 05:55 PM   #16
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Got it. Makes common sense, but in my opinion, the only stupid question is the one not asked.
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Old 07-11-2018, 06:52 PM   #17
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Like extreme load difference. Shut one engine down on a twin and the remaining engine is operating at a way different load and rpm. A considerably higher load. Much like running your single tied to the float at it’s normal cruising rpm. Much higher load.
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Old 07-12-2018, 12:03 PM   #18
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[QUOTE=Al;680329]
Quote:
Originally Posted by sanychsamara View Post
Hummmm, brazzen comment. Save to say from a distance of a boat that has the product installed and would be available for personal determinations.

For what reason other than offering a personally known solution to the forum, would I proffer something than had no benefit? The offering was made knowing that there are many sound material available at what cost?
You did reduced noise, I never doubted it . But it was not the best way to spend your money for the engine room insulation. You spent probably ~$2/sqft and got ~2dB noise reduction. That is $1 per sqft per dB. With DIY foam + MLV board you would have blocked ~10dB for $3/sqft, a 3x more effective way to spend your hard earned money
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Old 07-12-2018, 12:13 PM   #19
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I have twin engines and I can't imagine how the sound could be less with twins vs a single? I mean, you have 2 sources of noise instead of one. Rarely, I run one engine and no contest its definitely quieter with one running instead of 2. As has been said, the 2 engines resonating against one another at certain RPMs is the worst, but that is easily fixed with a slight rpm change and making sure to synchronize them.

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Old 07-12-2018, 01:10 PM   #20
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It's going to vary based on how the builder designed the boat. One built with sound-deadening in mind from the start is likely to be much quieter. A twin engined boat built that way would very likely be quieter than a single that didn't. So you'd have to know how the boat was built to make that comparison.

That and you'd have to know that the insulating materials were in good condition. I know on my Eastbay that the salon engine room hatch insulation matters quite a bit. Just the .75" wide strip running around the hatch blocks a notable amount of noise. The foam in mine has long since failed, likely due to age, heat and the pressure of it being compressed. Stand on the hatch and the noise level drops noticeably. It's the higher-end noise (turbo spinning, air intake). One of my 'to do' items. But open the hatch and you get an anvil chorus level of racket from the C-12 engines. So the thickness of the hull and the built-in sound insulation are doing quite a lot to block the rest of the noise.

So it's not just about number of engines, it's about how the boat was designed to manage their noise and how well those materials are still functioning.
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