transom exhaust is too loud

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Mark Brandly

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Hi all
I have a 77 stamas, fresh water cooled 350 mercruiser with above water transom exhausts.The two 3" pipes have a marine inline mufflers and are about 4 feet long each, measured from the riser to the transom.
The boat is too noisy for me even though I do enjoy the rythmic sound of the v8.
My question... can I install an elbow piece on the outside and lead the exhaust under water.
It seems like a simple solution to me.
 
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insanity

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Re: transom exhaust is too loud

It would work but look silly, also think about the drag forces involved.
 
roncoop75

roncoop75

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Re: transom exhaust is too loud

Mark Brandly said:
Hi all
I have a 77 stamas, fresh water cooled 350 mercruiser with above water transom exhausts.The two 3" pipes have a marine inline mufflers and are about 4 feet long each, measured from the riser to the transom.
The boat is too noisy for me even though I do enjoy the rythmic sound of the v8.
My question... can I install an elbow piece on the outside and lead the exhaust under water.
It seems like a simple solution to me.
Click to expand...

Will this be a problem:

Say you shut down the engine, now you have a sealed section of exhaust gas, cooling, contracting and tending to pull water back into the exhaust system.

I have no idea if this would be a problem, I'm sure it's been tackled by boat builders before. Do they vent the system some how?
 
jtmarten

jtmarten

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Re: transom exhaust is too loud

I've seen it done, as said before it just looks silly. Can't imagine a SBC with mufflers being very loud. Are the muffers still in good working condition? If the Y pipe is still installed, why not just switch back to thru-hub?
 
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Mark Brandly

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Re: transom exhaust is too loud

Thanks for the advice.
I must also ad some info.
The boat is a inboard, there is no y pipe, each exhaust manifold goes back and has its own exhaust pipe and tip.
The inline mufflers are new, about 12' long and did very little in terms of noise reduction.
My chief concern is water flowing back towards the engine (wake) or/and the vacuum created by the engine at idle or is the cooling water going to back up as it is recycled down the exhaust pipes into the ocean?
Looks and speed are not an issue. It is a 26' single engine (heavy) fishing boat and I keep the rpm's under 3000.
The tips are well covered by a large swim step which is about 6"above water.
 
jtmarten

jtmarten

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Re: transom exhaust is too loud

The exhaust system should have a drop of x inches. Don't know exactly what x is, but there needs to be a drop so water flows to the transom. Does the system have any flappers? If you have flat cut tips, you can install simple rubber external flappers that'll keep water out when you stop quickly.
 
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Mark Brandly

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Re: transom exhaust is too loud

Today I dove below the swim step (brrrrrrr...Pacific), removed the two rubber flappers, measured the od on the tips.
Went to the hardware store, bought two beefy 90 degree rubber elbows from general plumbing...50 bucks for both.
Tomorrow is the big day.
A second dive will see the installation and hopefully the result of an exhaust noise only equaled by a Duffy.
Just kidding...Thanks for all the great replies!
 
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Mark Brandly

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Re: transom exhaust is too loud

Dear friends
It is done...I installed the rubber elbows. I drilled a quarter inch hole above the water line for all eventual vacuum issues.
The result is AMAZING...the exhaust sound is hardly audible and consists of water bubbles.
I am mighty proud and thankful for all your input.
It looks good too. The photo shows the fruits of my labor.
Yours
Mark
 

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Mark Brandly

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Re: transom exhaust is too loud

Hi eliminator
At first I couldn't figure out what you meant, and then I saw it too and IT DOES look like a rock !
What you are looking at is the top of a Benett trim tab with minor marine growth on it.
Yours
Mark
 
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VaBeach1234

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Re: transom exhaust is too loud

I have 26' Trojan (similar exhaust noise issues as yours) and was wondering how far below the water do the elbow tips extend? Also, how far above the bottom of the boat are the tips. I assume they don't extend past the bottom of the boat so they are still out of the water when you are on plane. Correct?

Great looking setup.

Thanks.
Ken
 
Bondo

Bondo

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Re: transom exhaust is too loud

I assume they don't extend past the bottom of the boat so they are still out of the water when you are on plane. Correct?
Click to expand...

Ayuh,... That's the ticket....
 
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