I'd like some quiet Please?

BSnB · Dec 24, 2011

I have twin Crusader 4.3L Direct Drive V6's on my 28 foot 1987 Chris Craft Express Cruiser. The boat is new to me and I'm doing some renovations and improvements. At idle the engines are quiet, but on acceleration and cruising speed the exhaust noise is deafening. What I assume are factory mufflers are installed in-line. They are a barrel type with the exhaust entering on one end after the exhaust "T" and exiting the other end of the muffler before taking a 90 degree turn out of the side of the boat.

My questions are...Should they be this loud? Do marine mufflers wear out? I know the engines need to be tuned up, but they are running fairly well. It seems that I have sufficient water flow from the pumps, but I'll be replacing the impellers anyway this Spring to be sure. I'd rather not spend money on new mufflers if there is something I can do to make these quieter.

I look forward to advice from the Guru's. Merry Christmas everyone!

GA_Boater · Dec 24, 2011

Re: I'd like some quiet Please?

BS - could you put up a pic to see what your set-up is? Might help.

BSnB · Dec 25, 2011

Re: I'd like some quiet Please?

Sorry, GA_Boater, I don't have a photo and the boat is all shrink wrapped for the winter. My drawing skills suck, but here's a sketch of the layout.

The Risers loop up from the exhaust manifold and then curve back down to the exhaust pipes where they meet up at the crossover. A single exhaust pipe exits the crossover and angles down and back to the muffler. The muffler looks like a 5 gallon bucket laying on its side with the exhaust pipe entering one end and the tail pipe exiting the other before turning out and thru the hull. That's one bad drawing.:facepalm:..but I hope it helps illustrate the set-up.

Merry Christmas!!!

GA_Boater · Dec 25, 2011

Re: I'd like some quiet Please?

That's a good drawing, much better than I could do and cleared up what I envisioned I'm not able to much help, but if the mufflers are original there is a chance the internals have eroded over the years. Hopefully some more knowledgeable folks will chime in soon

Merry Christmas.

BSnB · Dec 25, 2011

Re: I'd like some quiet Please?

Thanks, GA_Boater. It's baffling (pun intended). Maybe the mufflers can erode inside. No way to check without destroying them I guess.

Bondo · Dec 25, 2011

Re: I'd like some quiet Please?

The muffler looks like a 5 gallon bucket laying on its side with the exhaust pipe entering one end and the tail pipe exiting the other before turning out and thru the hull.

Ayuh,.... What diameter are the pipes in, 'n out,..??
What levels do the pipes enter, 'n leave,..??

3, or 4" pipes allow a pretty fair Window to the insides...

In my experince, it don't get Quiet, til ya get the tips below water level, or in the wash at least...

gus-gus · Dec 25, 2011

Re: I'd like some quiet Please?

I am far from an expert, but believe the following;

Something has to absorb the sound. Usually this is done with chambers that are filled with a heat resistive fiber. This fiber is retained with a perforated metal or screen.
However some mufflers use chambers and baffling alone are used to smooth the sounds out, actually quieting or lessening the vibrations.

Other than that there only a couple fixes left. Directing the exhaust aft or place the outlet under water.

BSnB · Dec 25, 2011

Re: I'd like some quiet Please?

I'm pretty sure that the exhaust lines are 4", Bond-o. I know that the tailpipe exiting the side of the boat is that big. The exhaust pipe enters the muffler at a point somewhat higher than it exits, but essentially it's a straight shot through the muffler.

You can see in this picture the exhaust exiting out the side of the boat above the waterline. Getting these underwater or re-routed aft would be quite a challenge, gus-gus.

My expectation is not SILENCE with these big open pipes and it is fairly quiet at idle...just a low rumble really. However at speed the exhaust noise is quite loud and my expectation is that the mufflers should do more to deaden the sound. I am familiar with I/O's and OB's and the sound deadening qualities of underwater exhaust. This is my first experience with owning an Inboard. I've been on a friend's inboard ski boat with the exhaust tips exiting high out the stern and his boat is not even remotely as loud as mine.

I've had auto mufflers fail, of course, but the failure is usually an external hole rather than a failure of the internal fiber or baffles. I don't know the construction of marine mufflers, but I thought it was more about baffling and using the cooling water mixed with the exhaust to dampen the sound.

Thanks for taking the time today. Merry Christmas!!

gus-gus · Dec 25, 2011

Re: I'd like some quiet Please?

YUP BSnB, I see your predicament. However there are still only a couple areas which will change your outcome. Longer exhaust system might fix it, new and better muffs might do the trick, but the best and cheapest fix is a louder stereo! Or ear plugs.

BSnB · Dec 26, 2011

Re: I'd like some quiet Please?

I'll work on the loud stereo, gus-gus. Something I've wanted anyway!

I've seen these silencer inserts made out of stainless with baffles in them that you install in the exhaust line before the muffler. Any idea of the success from these? I also suspect that installing some sound dampening material on the engine access panels might do some good. What do you think?

BSnB · Dec 27, 2011

Re: I'd like some quiet Please?

I continued to think about this issue, in light of the advice I received from both of you...thanks Bond-o and gus-gus. I've focused on this being only an exhaust issue. I'd still like to quiet the exhaust some more, but I've realized that a big part of the problem might also be engine room insulation. As straight inboards, both engines sit directly below the Helm. There are three decks panels set side-by-side over the engines to provide access. These panels are plain fiberglass. There is no sound deadening insulation attached to these panels. In fact, there is no sound insulation at all in the engine compartment and I imagine the sound just bounces around in there and resonates the deck and gunwale walls.

Any thoughts on good sound insulation?

Bondo · Dec 27, 2011

Re: I'd like some quiet Please?

Any thoughts on good sound insulation?

Ayuh,.... On My barge, I went dumpster divin' for a pile of This stuff...
The stuff I got was considerably thicker, but it can be doubled, or tripled if needed...

My motorbox has 'bout 3/8" of the stuff, 'n the side curtains have 'bout a 1/4" of it...

It's muffled the sound Nicely, 'n it's closed cell, so's it won't hold water...

Since then, I dumpster dove another spot, 'n now have a nice selection of 1/2" stuff...

gus-gus · Dec 27, 2011

Re: I'd like some quiet Please?

BSnB said:
Any thoughts on good sound insulation?

You are correct that it is very likely adding to the exhaust note. my concern with your choice of insulation is fire proof or as a minimum, fire resistant material.
Because BOAT and FIRE don't play well together.
Personally, I would choose something exactly like this. KLIK

BSnB · Dec 27, 2011

Re: I'd like some quiet Please?

In terms of price, gus-gus, Bond-o's got ya beat. Although I don't know if I'd go dumpster diving for material that I can buy for about a penny per sq.ft.

On the other hand, $7 per sq.ft. for fire-retardant sound proofing isn't terrible.

Hmmm...I love bubble wrap. I wonder if I can find it made by inflating the bubbles with CO2. Sound proof AND a fire retardant that installs easily!!

gus-gus · Dec 27, 2011

Re: I'd like some quiet Please?

I use a product for aircraft (Piper Supercubs actually) that was light easy to apply, was actually bubble wrap that is foil faced. It was not fire proof, but being foil faced would be tough to ignite by direct means. KLIK
I used it on 5 or so Cub rebuilds and the owners loved it. It worked well for r-value insulation, I don't know how functional it would be for sound, but it is cheap.

BSnB · Dec 28, 2011

Re: I'd like some quiet Please?

I used something like this on my other boat, gus-gus, and it worked fairly well. Bond-o still has it beat on price for an engine compartment the size of the one I've got to do. I'm now considering doing the underside of the weather deck using a product like the Quiet Barrier stuff you first recommended and then go dumpster diving to find Bond-o's material for the sides. Failing that, the foil faced stuff for the sides might work pretty well.

I'm still going to explore reducing the exhaust noise. I can't help but think that it should be quieter and that something in the exhaust system is not functioning right.

Bondo · Dec 28, 2011

Re: I'd like some quiet Please?

I'm still going to explore reducing the exhaust noise. I can't help but think that it should be quieter and that something in the exhaust system is not functioning right.

Ayuh,... I'd pull 1 or both mufflers, 'n Look into it to see if it's baffled...

triman · Dec 31, 2011

Re: I'd like some quiet Please?

What about one of those ideas from left field, such as either a 90-degree elbow on the exhaust outlet, pointing down, to aim the noise away from the boat, or just a short length of tube, slit lengthwise and fitted to the exhaust.
The thought is to deflect any noise down or away from the hull.
Just my $0.02 plus tax and a happy new year to all.

BSnB · Jan 2, 2012

Re: I'd like some quiet Please?

I wondered about that as well, triman, but because the exhaust exits the side of the boat at the stern I wonder about having an exhaust pipe sticking out. I have seen some of those tailpiece extensions that have a silencer built in. They look like they might project out 2 or 3 inches and they are cut on the bias which might allow my to turn the exhaust down toward the water some. Would that then create a water scoop of sorts that might force water, in certain conditions, back up the pipe and into the engine?

Bondo · Jan 2, 2012

Re: I'd like some quiet Please?

BSnB said:
I wondered about that as well, triman, but because the exhaust exits the side of the boat at the stern I wonder about having an exhaust pipe sticking out. I have seen some of those tailpiece extensions that have a silencer built in. They look like they might project out 2 or 3 inches and they are cut on the bias which might allow my to turn the exhaust down toward the water some. Would that then create a water scoop of sorts that might force water, in certain conditions, back up the pipe and into the engine?

Ayuh,... Unless you move the dumps to the transom, I don't think this'll work very well, if at all...

I'd like some quiet Please?

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