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Old 05-07-2016, 07:46 PM   #21
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Ok, on the boat we're on right now with Twin Man 1200's. At 900 RPM, 62 decibels, at 1400 RPM, 66 decibels, at 1900 RPM, 71 decibels, at 2400 RPM, 76 decibels.

Our noisiest boat is a sport boat so open and at 1000 RPM, 71 decibels, at 1500 RPM, 74 decibels, at 2300 RPM, 80 decibels.

Our quietest boat at 750 RPM, 51 decibels, at 1500 RPM, 59 decibels, at 2450 RPM, 60 decibels.

I consider quiet to be a boat that never tops 70 decibels and noisy to be one that hits 80 decibels.

And, yes, we have a decibel meter. I've found the numbers on the testing sites to be within 2 or 3 decibels of real, however.
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Old 05-07-2016, 08:08 PM   #22
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My engines, JD 6068's, are under the saloon floor. I was curious about how much the wall to wall carpet helped with noise reduction. Numbers below, at 1750 rpm (8.5 kn) which is typical running speed:

Carpet in place - lower helm 70 dB Saloon 75 dB
Carpet removed - lower helm 80 dB Saloon 82 dB
Entrance to ER, door open - 99 dB

I was a little surprised at modest noise level variation between 1500 and 2000rpm. With carpet, 1500 rpm gave 73 dB at the helm, but was unchanged at 75 dB in the saloon. At 2000 rpm, helm was 72 dB and saloon was 78 dB.

Without carpet sound levels were the same throughout that rpm range at the helm but in the saloon increased to 86 dB at 2000 rpm.

I have subsequently put a mat on the saloon floor but have not re-measured the noise. It won't be as quiet as with the carpet which also had a a rubber underlay.

I should also note that the saloon floor has a number of hatches to the ER that provide a 6' x 6' opening. With better attention to sealing the bedding of the hatch (at present wood on wood) sound levels would be reduced.

On the bridge of course there is little engine noise, but I did not measure it.
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Old 05-07-2016, 08:20 PM   #23
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Definitely can hear the engine here. That's good because it gives a clue on the engine's state. Not loud enough, fortunately, to drown normal-volume conversations.
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Old 05-07-2016, 08:22 PM   #24
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My engines, JD 6068's, are under the saloon floor. I was curious about how much the wall to wall carpet helped with noise reduction. Numbers below, at 1750 rpm (8.5 kn) which is typical running speed:

Carpet in place - lower helm 70 dB Saloon 75 dB
Carpet removed - lower helm 80 dB Saloon 82 dB
Entrance to ER, door open - 99 dB

I was a little surprised at modest noise level variation between 1500 and 2000rpm. With carpet, 1500 rpm gave 73 dB at the helm, but was unchanged at 75 dB in the saloon. At 2000 rpm, helm was 72 dB and saloon was 78 dB.

Without carpet sound levels were the same throughout that rpm range at the helm but in the saloon increased to 86 dB at 2000 rpm.

I have subsequently put a mat on the saloon floor but have not re-measured the noise. It won't be as quiet as with the carpet which also had a a rubber underlay.

On the bridge of course there is little engine noise, but I did not measure it.
Sometimes it doesn't take a lot to make a big change as shown by your carpet.

On the lake we owned a 30' Cobalt Bowrider with twin 430 hp gas volvo I/O's. It was over 70 decibels at 1000 RPM or so, over 80 at moderate running speeds, and it topped 90 decibels at WOT. The dealer went to work trying to reduce the sound with some under cover insulation, with some sealing around the engine cover, and with some soundproofing under the seats that were over the engines, part of the engine hatch. It was a very powerful sounding boat, but wanting to keep our hearing plus be able to carry conversations on, we wanted it quieter. Lowered it 5 to 10 decibels depending on speed. Biggest difference was at cruise and WOT where it was very throaty.
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Old 05-07-2016, 08:26 PM   #25
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Tug,
Is that the sound of you and your friends breathing on the bridge?
on bridge and pilot house can't hear engine only noise from water on hull
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Old 05-07-2016, 09:23 PM   #26
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The carpet is a good point. My boat came with carpet sections cut and edged for the saloon floor. The carpet sits on top of that mesh non-skid stuff. I hadn't though about it, but that has to add a lot of sound insulation to the saloon. I love the look of the teak and holly floor, but I have to say the carpet is fantastic.
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Old 05-07-2016, 11:23 PM   #27
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twin 330 cummins

In the pilothouse at displacement speeds there is a low rumble. In the salon you can hear them but not so loud that watching a movie is bothersom.

At 2400 RPM cruise you can hold a conversation in the salon but watching a movie is not as plesant. From the pilothouse you can hear the engines but not so bad that normal quiet conversation is difficult.
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Old 05-07-2016, 11:40 PM   #28
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With the new 4 cylinder John Deere turning 1,400 rpm at cruise, the boat especially the pilothouse is very pleasant. It's so quiet I can easily here the engine room exhaust blower running.

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Old 05-07-2016, 11:44 PM   #29
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Mrs. Sanders climbs the steps to the pilothouse with a coffee for the skipper.
Kevin?
Kevin?
KEVIN!

Yeah hon, I'm down here watching Pretty Woman. Come join me.
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Old 05-08-2016, 12:09 AM   #30
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Each year, as I get older, the engine gets quieter.
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Old 05-08-2016, 06:36 AM   #31
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At least now I know why Detroits are called Screaming Jimmies.
That said it's quite OK in the wheelhouse.Saloon is good too.We are a galley down model,door to the ER is in the galley.Somewhat different down there.
I guess every boat is a compromise.Surprising what you get accustomed to.
I also have a unexplained attachment to Seagull outboards so noise obviously doesn't worry me.
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Old 05-08-2016, 06:44 AM   #32
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As we boat for pleasure , it cant be too quiet.

With a 6-71 just below our PH for long trips we use head phones .

I use ones with a built in radio, the bride loves books on tape , there is no conflict as we listen to different sources.

Eventually sound absorbing will be added to the overhead , although conversation is fine now , due to 2lb sq fr Soundown in the ER.

CH 16 can still be monitored with headphones on..
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Old 05-08-2016, 11:46 AM   #33
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At least now I know why Detroits are called Screaming Jimmies.
That said it's quite OK in the wheelhouse.Saloon is good too.We are a galley down model,door to the ER is in the galley.Somewhat different down there.
I guess every boat is a compromise.Surprising what you get accustomed to.
I also have a unexplained attachment to Seagull outboards so noise obviously doesn't worry me.
DD two stroke are call screeming Jimmies as they have been know by self feeding themselves. The fuel pump seal can fail, pumping diesel into the oil pan, when the level get high enough it will run away which sounds like screaming. Out 671 almost got to a point of doing that. Lucky I check the oil level and noted the oil level was increasing. so make sure you check the oil level for to much as well as to little.
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Old 05-08-2016, 11:52 AM   #34
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Oh, as to noise level it's very quiet after we changed from dry stack to wet,added a in line muffler and a modified water muffler with muffler wrap and carpeted the salon floor. The water splash out of exhaust of gen set is louder.
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Old 05-08-2016, 11:54 AM   #35
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Hawg- Mostly it is the difference in 3b vs 4b regarding noise. 4b has more pressure pulses, but each is less in magnitude. The DQX has a funky blade shape that the prop guys say often gets good results. So if I am going to 4b, I'm going to want the most efficient I can get. 4b usually has a little more drag than 3b. But like anything related to props, it's half science and half black magic.
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Old 05-08-2016, 12:13 PM   #36
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Couple o' sweet running Mercruiser 350's; top out at 255 hp each. Just below hull speed (around 7 knots / 7.58 is calced hull speed) with both running it's very quiet in salon, no sound on Bridge - 2 +/- nmpg. At full plane doing 16/17 knots - still easy to talk in reg volume in Salon. Very little sound on bridge - 1 +/- nmpg. Near WOT... in salon the 4 bbl's secondaries get to sucking big air input (gulping much fuel too! lol). In salon can hear that air suck and the high RPM of engines; still able to converse, albeit with a but more volume. On bridge - rushing sound of air past our ears and wooshing sound of water as boat cuts through doing 20 + knots... with powerful exhaust sounds is a pleasure to listen too. - High fuel usage is not pleasant to pay for!

If we want to really save on fuel burn... I sometimes run on one engine at 5 to 5.5 knots. Then she whispers with nearly no engine sound in salon. At that speed on one screw... we then get just under 3 nmpg.

Our Tolly is a very affordable, fully self contained, seaworthy, comfortable and fun water-craft to own for pleasure-time boating.

Happy Sound-Level Daze! - Art
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Old 05-08-2016, 05:37 PM   #37
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I was very surprised by the lack of noise on this CHB 34' I just got. Coming down from Bellingham at just over 1650 it was quite quiet in the cabin. I am quite hard of hearing so being in noisy places is a problem for me and conversation. No issues here.
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Old 05-08-2016, 06:43 PM   #38
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A good friend of mine has a 31 ft lobster boat with twin 3116 Cats. We sit on the lead foam lined engine boxes in the cabin. Easy cruise speed is 17 kts at 2050 rpm. At that speed we can carry a normal conversation without shouting. Crank it up to 2200 and the turbo whine grows but not yet earplug worthy. 2400 and I want earplugs for anything longer than 10 minutes. Peg the throttles and they make a subdued roar. 1500 rpm with a box ajar will have you looking for the ear plugs and muffs.
I have a sound meter app now and will take some readings next time out.
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Old 05-08-2016, 07:32 PM   #39
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A good friend of mine has a 31 ft lobster boat with twin 3116 Cats. We sit on the lead foam lined engine boxes in the cabin. Easy cruise speed is 17 kts at 2050 rpm. I have a sound meter app now and will take some readings next time out.
Lobster boat with tein engines? Not where I come from...
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Old 05-08-2016, 09:54 PM   #40
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Mrs. Sanders climbs the steps to the pilothouse with a coffee for the skipper.
Kevin?
Kevin?
KEVIN!

Yeah hon, I'm down here watching Pretty Woman. Come join me.
Spartacus actually
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