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Boat quiet?

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Re: Boat quiet?

Postby Rivernut » Sat Nov 14, 2020 5:52 am

I have people tell me they hear me coming from miles away. On cars they say a cross-pipe helps reduce the sound while increasing performance. My Eagle / Gator has a mild 350 with dual 4” raw water exhaust. a Anyone ever tried a cross-pipe in a boat?
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[video] https://m.youtube.com/watch?v=27Q3f4y6at4[/video]

[video] https://m.youtube.com/watch?feature=emb ... 4oJuaAt1RI[/video]
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Re: Boat quiet?

Postby viking » Sat Nov 14, 2020 11:55 am

Quiet... no wait, my speakers were off. Maybe that's the secret. Install a stereo and turn the speakers off. Then your boat will be quiet.
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Re: Boat quiet?

Postby Rivernut » Sun Nov 15, 2020 12:29 pm

Real Boats Don't Have Propellers!
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Re: Boat quiet?

Postby Riverjohn » Sun Nov 15, 2020 12:47 pm

Rivernut wrote:https://www.amazon.com/noise-cancelling-speakers/s?k=noise+cancelling+speakers

Let us know how it works.
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Re: Boat quiet?

Postby hilljackian » Mon Nov 16, 2020 11:31 am

Speaking of air in the pump, many of you will recall the "air-bleed" lines that where on the 3-stage Hamilton (and clone) pumps. The expressed purpose of this system was to quiet the notoriously loud 3-stage. It consisted of a tube that ran from a port in the pump at the transom into the intake housing. It connected atmospheric pressure (through the pump port) to the suction of the intake, which means that air was flowing into the intake of the jet pump. Assumedly it helped because they included this equipment on not only on the old Hamilton's but the current production Flo-Pros.

However, injecting air into the pump is counterintuitive to the common consensus that eliminating air in the pump helps reduce noise. My best effort at getting an answer as to how this air-bleed system worked produced a weak explanation along the lines of "the injected air reduces harmonics in the impellers, thereby reducing noise." Which, to me is equivalent to saying "some kind of magic happens." Can anybody explain this better? Does anybody have a 3-stage with an air-bleed system that can confirm it works to reduce noise?
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Re: Boat quiet?

Postby Justboatn » Mon Jan 11, 2021 11:15 am

I removed the internal mufflers and added two external ones. It seems to have helped but I haven't used a sound meter yet. My phone said 89 at wot. When viking tested it it was 91 wot with a meter.
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Re: Boat quiet?

Postby viking » Wed Jan 13, 2021 10:44 am

Indeed, we should test with same meter. Where did you put your boat in that is ice free? Also, the 91 db was at cruise rather than WOT, so 89 at WOT may mean 85 at cruise (or something).
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Re: Boat quiet?

Postby Justboatn » Fri Jan 15, 2021 7:18 am

I tested it awhile ago. I left the factory mufflers on after I put the exterior ones on and tested it. It was very similar to the original numbers. I pulled the interior mufflers and installed new rubber hose and got the results I posted. I think the rubber exhaust hose deadens the sound alot better than the metal mufflers inside the engine compartment.
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Re: Boat quiet?

Postby viking » Sun Apr 04, 2021 7:21 pm

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Re: Boat quiet?

Postby Justboatn » Mon Apr 05, 2021 10:02 am

Did you do any testing on the stiffeners alone?
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Re: Boat quiet?

Postby viking » Mon Apr 05, 2021 10:21 am

Yes to stiffeners only. About 2 dB. But there is some uncertainty on this.

1) The dB meter is bouncing plus or minus 2 dB from the "average" my brain selects, so uncertainty is significant.

2) It seemed to reduce the bass more than 2 dB. This may have been my wishful thinking, or it may be related to the way the dB is calculated. I'm too lazy to research, but it's probably something like amplitude x frequency. Given the low frequency of bass, a high amplitude may measure as relatively low dB. So completely eliminating the bass may not affect the measured dB very much. I welded mine, so there is some scorched paint and minor hull rippling. I thought to just use epoxy, but this was a no-go due to extreme force required to push the side back to flat: it was slightly bowed due to use.

Overall, the minus 5 dB significantly reduces the thought "I need some ear protection." But conversation will still require some yelling. Food for thought is the suggestion that luxury automobiles are... quiet.
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Re: Boat quiet?

Postby Justboatn » Mon Apr 05, 2021 1:14 pm

I like the idea of getting the reinforcement back there and helping to reduce the noise. Thanks for the information.
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Re: Boat quiet?

Postby Nater11 » Mon Apr 05, 2021 5:24 pm

viking wrote:Food for thought is the suggestion that luxury automobiles are... quiet.


Also, luxury vehicles are twice the weight of similar sized cars... (Bentley Gt almost 6k lbs) something to that me thinks.
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Re: Boat quiet?

Postby viking » Mon Apr 05, 2021 5:51 pm

On the other hand, my 2002 Ford Taurus was very quiet even at full throttle. And on the other hand, I had a Ford cargo van that had zero interior behind the front seats. This made it very loud when the road was wet due to spray into the wheel wells.
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Re: Boat quiet?

Postby viking » Wed Apr 07, 2021 12:14 pm

So I decided to research how ambient noise meters typically weight various frequencies. It turns out this is a very standard and uniform process as per line A below.

Interpreting the x-axis (frequency), 20 is about the lowest bass you can perceive, while 20K is about the highest. 100 is a low male speaking voice, and 1000 is a very high soprano.

The y-axis (Gain dB) is the weighting applied to the frequency. -6 means it is cut in half. -12 means reduce by x4. -18 means reduce by x8. The frequencies that carry maximum weighting (no reduction) are roughly 1000 to 6000. It turns out the leaves rustling are in the upper portion of this range, which makes sense from an evolutionary perspective. (Old people can't hear well at high frequencies, which is why it's easy to sneak up on them.)

So low bass tones in boats are nearly ignored in dB meters. But... if you are interested in conversing with male voices, then this unweighting is deceptive. If you completely remove the boat's bass, this will have little effect on the meter, but conversation will be much easier.

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