Cabin noise

[melissar]

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?

 

[sunchaser]

At anchor a go fast with bikini twins and a single guy is quite nicely noisy.

 

[melissar]

Not really my demographic, but okay then!

 

[Al]

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

 

[sanychsamara]

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 3 PDFs/Handbook.pdf

 

[Al]

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
Click image to open expanded view
Carinsulation.com
Car Insulation - 4' x 10' Roll (40 Sqft) Sound Deadener & Heat Barrier Mat - Automotive Lightweight Thermal Insulation
4.5 out of 5 stars 94 customer reviews | 61 answered questions
Price: $49.99

 

[sanychsamara]

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.

 

[High Wire]

Definitely more noise from twins. ?

 

[melissar]

Hmmmm...one person on here says slightly less noise, one says definitely more.

 

[Airstream345]

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.

 

[Irish Rambler]

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.

 

[Al]

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

 

[Nomad Willy]

Definitely more noise from twins. ?

It’s a question of where the noise comes from.
One would think it’s a question of work being done. I had a diesel Nissan Maxima in the 90’s 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 25’s 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 I’d 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 “oil can’ continuously. That’s 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 there’s 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.

 

[Fletcher500]

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.

 

[High Wire]

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.

 

[melissar]

Got it. Makes common sense, but in my opinion, the only stupid question is the one not asked.

 

[Nomad Willy]

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.

 

[sanychsamara]

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

 

[kchace]

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.

Ken

 

[wkearney99]

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.

 

[Al]

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

 

[melissar]

Thank you, Bill, most helpful. We are looking at GB 36s, with both twin and single, and irregardless of the other considerations, thought this was something to factor in. Your reply makes sense.

 

[Rcd]

Boat noise

Interesting volley of opinions most have merit however bang for the buck appears to be in play. Before I start lining the boat with a myriad of products, floating machinery away from hard sufaces etc. I would first make sure motor mounts are optimal, shafts are aligned and the props have been properly serviced. Both motors should be checked for accuracy to the tachs etc. Then find it's happy place (rpm) to run the boat. After all of that begin to look at stopping the remaining noise.

 

[wkearney99]

Interesting volley of opinions most have merit however bang for the buck appears to be in play. Before I start lining the boat with a myriad of products, floating machinery away from hard sufaces etc. I would first make sure motor mounts are optimal, shafts are aligned and the props have been properly serviced. Both motors should be checked for accuracy to the tachs etc. Then find it's happy place (rpm) to run the boat. After all of that begin to look at stopping the remaining noise.

It also helps to be able to take a trip on more than one of a particular model/year. Not always possible but potentially worth added expense/effort. This way you'll have a feel for how the brand/model is "supposed to" feel, versus how just the one example you're considering as a purchase might feel.

 

[Trawlerman]

The boat build, the engine intake filter (if any), and the condition of the motor mounts are the overwhelming factors in the cabin noise. For example, in my 50' Marine Trader with twin 160 HP Perkins, the noise traveling is much less than my buddies 36' Marine Trader single, but the comparison is not apple to apple. I mention the motor mounts and the intake filter as many people have no idea how much they contribute to noise. Another factor is what "kind" of noise. Two equal dB readings don't necessarily "register" on people as equally loud. Some sounds are much more annoying than others.

 

[FlyWright]

As mentioned above, so many variables that it's hard to say one is louder than another. I've been on some twins that were MUCH quieter that other singles but in general, I'd think with twins and singles on the same model, twins will be more noticeable in noise and/or vibration. There are methods for reducing both.

I have twins on an old boat that suffered a sagging house. I installed adjustable struts made of steel pipe in the ER to improve the support and raise the house to its original height. (Thanks Cpseudonym!) This transferred more vibrations into the salon floor. Adding sand to the pipes that supported the floor greatly reduced the vibes transferred to the decking.

I also installed a sound-barrier carpet underlayment designed to attenuate the noise made by Soundown. (Thanks, Keysdisease!) It cancels a good portion of the mid- and high-frequency noise but not so much help at the lowest frequencies. It's done a great job of quieting the boat and softening the feel under foot.

 

[ranger58sb]

I also installed a sound-barrier carpet underlayment designed to attenuate the noise made by Soundown. (Thanks, Keysdisease!) It cancels a good portion of the mid- and high-frequency noise but not so much help at the lowest frequencies. It's done a great job of quieting the boat and softening the feel under foot.

My measuring device wasn't sophisticated enough to address various frequency ranges, so I only got total dB differences, before and after. Turns out it doesn't seem like much of an improvement on paper, but it still seems quieter, both for mains/genset together and only genset.

And yes, definitely softer underfoot! That right there was worth the price of admission for me!

I thought it odd that in both before and after tests, our twins are louder at idle than they are at 1200 RPMs.

-Chris