Underwater exhaust pros and cons

Old Mud

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WoundUpMarine

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Old Mud

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Diesel Jerry

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SSTIDD7

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And so you constantly have the urge to take a leak yourself.

:D
Reading this post that was my first thought. I had a Henriques with exhaust built into the double chine. Worked well but that tinkle of water all day!
 

Blitzen

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Bringing this one back up as it's a good idea for my Duffy, I want to try and keep the stern clean, with less soot and this seems like a great solution. @Blitzen do you have any pictures of your 36 or the new boat's underwater outlets? I'm curious how much of a lip is used to create a good vacuum while cruising ahead.
John,
Here are a few pictures I dug up, you don't need much of a brow in front of the tube a little goes a long way, to too big will cause problems. I will try and find a better picture from the side so you can see it better. The port on
the starboard side of the transom is the relief line for when the boat is not moving.

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Blitzen

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John,
On the new boat we went with dual underwater and no telltale, but I did buy a temperature alarm for the exhaust elbows which should alert me long before we have a problem. Also if there is any doubt down the road or excessive back pressure in the system a telltale can be added easy enough to divert some water and act as an indicator.
For me the best thing about the system is not smelling the diesel exhaust on those hot calm days trolling offshore.
 

Old Mud

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Blitzen

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Not to mention all those folks that ask, "Where the hell is your exhaust" And you say, well it's up on the house top where no one can see it. :p
Don, the look of the faces when I would tell people the HP of the engine and then they looked down and see the exhaust port on the stern. They would give me a blank look and say oh yeah, ok and walk away scratching their head like I was the crazy one. I am sure they were thinking that there was no way I had that much HP with that little exhaust line in the transom.
 

HUNTHARD

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I have dual underwater exhaust on my Wesmac. It's an amazing system. Gotta be 75% quieter when running compared to other boats. We also have a relief tube out the back when at idle or slow trolling water and exhaust comes out the back. I agree these fish feed right off the back of draggers way louder then my boat. I never smell fumes and never have soot on my transom. Genny is the same way. I hear the motor run but not the exhaust noise. It's very easy on the ears after a two day trip, all you hear in the cockpit is wind and water. No drown from the engine. I would highly recommend it on any NEW build. My muffler in the engine is made by sound down and is about 4ft wide and 3.5ft tall feeding dual under water exhaust. My wife loves to fish with me and has never once complained about the fumes since ownership.
 
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Tunacious

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every henriques I have seen has under water exhausts, know a bunch of owners who do well tuna fishing
my only concern would be introducing air and a bubble stream ahead of the prop.
I owned a 28 express. The under water design was an opening above the recessed trim tabs. It also had an oval slot in the transom for when the tabs were pulled up. I loved it. Henriques also incorporated a water lift muffler design into the exit. Very quiet. I'm a Marlin guy and the boat raised Marlin better than any other boat I owned. I believe BFT are more sight hunters and any noise is irrelevant.
 

Downrigga

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One downside would be not being able to see or maybe hear whether raw cooling water is pumping through the exchanger into the exhaust. My GM 26 has a diverter at the transom that directs the exhaust to a point a few inches below the waterline. I miss not being able to hear and see the raw water exiting the exhaust just so I know immediately if there is a problem with the raw water cooling loop. (Are those diverter units really useful? Should I take it off?)
Have no fear. The box that the underwater exhaust goes thru has a small seperate pressurized compartment. On top side of the compartment is a small tube that is tied into the. 2" above water line exhaust so you can see the water coming out.
 

WoundUpMarine

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WoundUpMarine

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Downrigga

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That is WAY more involved than what I was going to do on my boat. Looks awesome, clean set up and great use of a tube for water flow.
Its actually very easy to make. The bottom 2 " white hose has nothing to do with the exhaust system.
 
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