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Old 05-08-2016, 11:30 PM   #41
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My 40 year old cruiser with 6-71s had only some acoustic tiles on the engine room liner and carpet in the saloon. Even in the pilothouse I have to admit that I suffered from noise fatigue on long 5-7 day cruises. Never did take an acoustic reading, but it couldn't have been good, probably in the 70+ db range.

My 20ft CC has a 4 stroke outboard, only 60hp, but after an hour of straight cruising I start disliking the noise. Will measure it with the phone app this weekend to have an idea of what my ears consider to be uncomfortable.

On our construction sites I would build a plywood box with one open side and fit it on top of the portable genset, with the open side facing away and reflecting the noise. Cut noise more than half. I have been considering building a similar fiberglass cover for my o/b.
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Old 05-09-2016, 12:01 AM   #42
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My 20ft CC has a 4 stroke outboard, only 60hp, but after an hour of straight cruising I start disliking the noise. Will measure it with the phone app this weekend to have an idea of what my ears consider to be uncomfortable.

.
I didn't even mention center console but a typical CC with triple 300's goes from 70 decibels to 90 decibels depending on speed and it's not a regular curve as at certain RPM it jumps up and then back down a bit.

I also found a test on an 15' Edgewater with a 60 hp Yamaha. Very similar. Starts at 67-68 decibels, then at cruise it's around 81 decibels and at WOT it's 90 decibels.

One thing about outboards too is that they're not just loud for whoever is in the boat, but loud for all around it too.

I'm surprised we haven't seen more boats with covers over the outboards.
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Old 05-09-2016, 12:20 AM   #43
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Originally Posted by makobuilders View Post
My 40 year old cruiser with 6-71s had only some acoustic tiles on the engine room liner and carpet in the saloon. Even in the pilothouse I have to admit that I suffered from noise fatigue on long 5-7 day cruises. Never did take an acoustic reading, but it couldn't have been good, probably in the 70+ db range.

My 20ft CC has a 4 stroke outboard, only 60hp, but after an hour of straight cruising I start disliking the noise. Will measure it with the phone app this weekend to have an idea of what my ears consider to be uncomfortable.

On our construction sites I would build a plywood box with one open side and fit it on top of the portable genset, with the open side facing away and reflecting the noise. Cut noise more than half. I have been considering building a similar fiberglass cover for my o/b.
Well, I know what 70 dB sounds like as I posted above. Not that bad at all, doesn't disrupt conversations. I suspect your 6-71's would have been closer to 90 than 70. I know what 3-71's sound like, we had them on the farm. My older brothers are partially deaf, partly due to the 3-71's and partly from tractor transmission noise.
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Old 05-09-2016, 12:27 AM   #44
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My 40 year old cruiser with 6-71s had only some acoustic tiles on the engine room liner and carpet in the saloon. Even in the pilothouse I have to admit that I suffered from noise fatigue on long 5-7 day cruises. Never did take an acoustic reading, but it couldn't have been good, probably in the 70+ db range.

My 20ft CC has a 4 stroke outboard, only 60hp, but after an hour of straight cruising I start disliking the noise. Will measure it with the phone app this weekend to have an idea of what my ears consider to be uncomfortable.

On our construction sites I would build a plywood box with one open side and fit it on top of the portable genset, with the open side facing away and reflecting the noise. Cut noise more than half. I have been considering building a similar fiberglass cover for my o/b.
WAYYYYY Back When (mid 50's) - Dad built plywood hatch that sat in front of the 25 Johnson outboard on small cuddy-cabin family cruiser. Cut down the noise a lot! I remember that well... also, made mom really pleased!
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Old 05-09-2016, 06:22 AM   #45
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https://books.google.com/books?id=Y-...boards&f=false

Noise Control POLYFORM® Molded Outboard Motor Application | Polymer Technologies, Inc.
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Old 05-09-2016, 06:30 AM   #46
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I helped deliver a 46' Post with a pair of 6-71 Detroits. The skipper handed out ear plugs when we left the dock. Even on the fly-bridge you needed them.

Hobo's pretty quite. The pilot house is great as is the fly bridge. We have throw rugs/pads over the engine hatches which cut down the noise considerably.
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Old 05-09-2016, 06:38 AM   #47
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In the beginning of this thread there was a link to the logSPL app that I decided to download and play with. It turns your iPad or iPhone into a sound meter and it is reported as accurate...
Anyway, yesterday we drove 200 miles in my Cummins powered Ram and I had the phone on indicating sound levels with the app.
In general, driving at speeds between 0 mph and 70 mph depending upon throttle position, we saw a general range of between 60 dBa and about 80 dBa...
Now I intend to compare those numbers with the sound levels measured on the AT 395 with the Cummins 6.7 on Wednesday.
I'm not sure I fully understand the ins and outs of using decibels for sound measurement but perhaps this will help me build on the understanding...
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Old 05-09-2016, 06:45 AM   #48
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Our boat is as loud as a sawmill, well not quite but it gets loud at anything over 1400 rpm's. Flybridge is where we hang out so not a big issue for our type of boating.
Twin Cummins 5.9 6BTA, 250hp each.

Throw the gen into the mix (8KW gronan) and it sounds like a symphony of construction equipment.
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Old 05-09-2016, 06:58 AM   #49
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BB - The April 1931 Popular mechanics (with outboard cover blurb) is a hoot! Any Idea who made notations all over the Pages?
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Old 05-09-2016, 09:00 AM   #50
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Lobster boat with tein engines? Not where I come from...
True, not for lobster, but for tuna. JC Casco Bay 31 built in New Hampshire.
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Old 05-09-2016, 09:31 AM   #51
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My own preference is the quieter the better. Our pilot house is mid 60 db, salon a db or two louder, and the boat deck and fly bridge are mid 70s because you are closer to the dry exhaust outlet. I spent a bunch of time trying to figure a way to quiet down the fly bridge even more, and was close to installing a second muffler, but then found it would exceed the engine back-pressure allowance. The only way to fix it would have been to enlarge the entire exhaust from 5" to 6" or more, so that killed the project.

I agree with BandB on the target levels. 60s is good, and anything over 80 is just too loud. We had a Back Cove 29 that ran just over 90 at the helm which was completely unacceptable. My wife and I both had to wear ear plugs, and still couldn't talk to each other wile underway on a plane.
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Old 05-09-2016, 10:40 AM   #52
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BB - The April 1931 Popular mechanics (with outboard cover blurb) is a hoot! Any Idea who made notations all over the Pages?
No idea, but I thought it was funny.
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Old 05-09-2016, 10:45 AM   #53
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There are many decibel guidelines to both compare levels to other things and to tell what is likely to cause ear damage. For instance, they say 85 dB is safe up to 8 hours, but 94 is only safe for an hour.

Dangerous Decibels » How Loud is Too Loud?

Hear are some very good charts, slightly different numbers. I found it interesting that 85 is like traffic when you're in a car but 95 is like a jackhammer from 50'.

http://www.gcaudio.com/resources/howtos/loudness.html

I've dealt with sound a lot in business. We had jobs that exposed one to noisy and required the wearing of ear muffs in those job. We had a lot of battles with employees who would be seen without. It was a fire-able offense.
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Old 05-09-2016, 11:01 AM   #54
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My 40 year old cruiser with 6-71s had only some acoustic tiles on the engine room liner and carpet in the saloon. Even in the pilothouse I have to admit that I suffered from noise fatigue on long 5-7 day cruises.
The effect of noise on fatigue is something that I had not considered until a few years ago when making a road trip in my 350Z. I have several exhausts for the car and at the time had a race exhaust that wouldn't break the newer 100db noise limit for SCCA Autocross. It is still pretty noisy and the 350Z has a lot of interior road noise as well depending on road conditions. I found that using ear plugs made a huge difference in fatigue level on a 12 hour road trip. I would bet the same is true for a 6 hour run in a boat when the noise levels are higher.

One of the things that sold me on my new boat was how quiet it was during the sea trial. Even last weekend when a mechanic reinstalled my HX and aftercooler, he and I were chatting in the saloon with the engine running at 1300 rpm with all the engine room hatches open. The QSB is pretty quiet.
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Old 05-09-2016, 12:17 PM   #55
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That QSB is SOOO much quieter than it's predecessor 6BTA, especially at low load. Believe it not, most of the 6bta noise at low load is timing gear lash. I think the CR pump on the Q keeps the lash in one direction. Big difference.
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Old 05-09-2016, 02:13 PM   #56
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The new 6.7's are even quieter. Take a look..
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Old 05-09-2016, 02:16 PM   #57
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That is Cummins QSB 6.7's, sorry about that.
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Old 05-09-2016, 04:42 PM   #58
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The new 6.7's are even quieter. Take a look..
That was no load, I guess? Also, what rpm levels were used? - Thanks, Art
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Old 05-09-2016, 05:49 PM   #59
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I bought my spouse a set of noise-cancelling headphones for Christmas. She likes to wear them on the boat--in fact, she seems to be wearing them around the house as well. Hmmmm
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Old 05-09-2016, 06:00 PM   #60
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Anyone here realize that noise levels double every 3db, thus lowering tolerance by half? Just a little fyi...
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