exhaust musings

rooferdave · Post by **rooferdave** » Sun Nov 13, 2011 11:35 am

both my neighbours in my club have trojan 44's a 1976 and a 1980, the 76 has the exhaust pipes at the rear and are under water making his boat super quiet... could I do this?

alexander38 · Post by **alexander38** » Sun Nov 13, 2011 4:01 pm

that's a good question, thought about that to. I'd worry about water backup if the risers are to close to the water line, h'mmmm boats...

aaronbocknek · Post by **aaronbocknek** » Sun Nov 13, 2011 4:08 pm

hi dave, your tri cabin has the rear mounted engines with v-drives right? if i recall from the tri cabin i grew up with, the mufflers were the straight line models that ran off the manifolds hugging either the port or starboard side of the boats interior. i don't think your boat can be retrofitted with the type of underwater exhaust system my tri cabin has or the one's you mentioned. i did do a google search for 'marine underwater exhaust systems' and i fount two websites that might be of interest to you and others. the current set up that i have i hate for one reason. there is a 5" hole that goes right through the boat with no way to shut it off if i have to swap out an exhaust hose, or, god forbid, the bellows goes bad. i've pondered ways around this but from what i've read on line, the exhaust exiting the boat from under her actually lifts the hull up and gets her on plane faster. i'm still researching this. here are two sites that i've come up with that you might like to look at.
let me know what you think.
aaron

http://www.vonwidmanndesigns.com/home.html
http://www.freshairexhaust.com

Torcan · Post by **Torcan** » Sun Nov 13, 2011 4:18 pm

aaronbocknek wrote: the current set up that i have i hate for one reason. there is a 5" hole that goes right through the boat with no way to shut it off if i have to swap out an exhaust hose, or, god forbid, the bellows goes bad.

5 " hole through the hull underwater with no way to shut it off..!!!!!!

That is some scary "crap"

aaronbocknek · Post by **aaronbocknek** » Sun Nov 13, 2011 4:30 pm

Torcan wrote:
aaronbocknek wrote: the current set up that i have i hate for one reason. there is a 5" hole that goes right through the boat with no way to shut it off if i have to swap out an exhaust hose, or, god forbid, the bellows goes bad.
5 " hole through the hull underwater with no way to shut it off..!!!!!!

That is some scary "crap"

you said it. if you send me your email addy, i'll send you a pic of the set up. it scares the sh$$%#@ out of me knowing that there is no way to 1. shut off the system if the bellows goes bad, and 2. the boat has to be hauled to change out the exhaust hoses. centek industries built it for trojan and still can make the part. i've got the drawings they sent me in may of this year. anyway, the centek system is a 5'' dia collector with two 3'' tubes that take the engine water/gas and blow it down the 5'' hole thru the bottom of the boat. that also has a 1.5" bypass that is used at idle and low speeds that exit the boat on the side. the centek collector is then mounted on top of a rubber/neoprene ribbed bellows (think lost in space robot arm). that in turn is mounted to a bronze 5" through hull fitting. under the boat, there is a multi port pan flute exhaust system that allows water to flow through and carry the fumes and water away. it looks like a mini jet engine. clever, yes, i guess. why there is no way to shut anything off is beyond me. i want to swap out the cast iron 90 degree elbows for glass, but my mechanic said that the boat has to be hauled to do it as there is 16,000 pound of boat pushing up. can you imagine the water flow if one of those hoses or the bellows goes bad. it turns my stomach every time i think about it.

rooferdave · Post by **rooferdave** » Sun Nov 13, 2011 8:24 pm

the fresh air exhaust looks cool! I am going to the club soon and am going to look at the other trojans exhaust, as I recall it was only downturns into the water, and yes my exhaust is as you describe Aaron only mine was custom built by me

rooferdave · Post by **rooferdave** » Thu Dec 22, 2011 3:32 pm

took a while but this is a pic of the trojan 44's exhaust

rbcool · Post by **rbcool** » Thu Dec 22, 2011 4:22 pm

Is that toilet paper coming outta the exhaust??

Ron

prowlersfish · Post by **prowlersfish** » Thu Dec 22, 2011 5:42 pm

Dave you can refit yours like that . But you need a relief hole above the water line

Paul · Post by **Paul** » Thu Dec 22, 2011 7:33 pm

I made this one out of fiberglass and West System resin. I installed this mostly to help reduce the exhaust vapors in the cockpit from the "station wagon effect". I'd say it took care of about 80% of that problem plus it made the boat much quieter.

It has no relief holes above the water line and no back pressure problems. I believe that this is because it doesn't exhaust any deeper in the water than the relief holes on an I/O.

Since it hangs down below the hull, I ground out a line all the way around it that is flush with the bottom of the hull to basically create a weak point on the exhaust boot. That way if I should hit anything in the water it will shear off at that point. I proved it out a few years ago when I hit a dead head floating in the water and it sheared right where I planned. The repair was done right on the boat at haul out that fall.

Below is a photo of it that was taken when I was winterizing the engine a couple of years ago.

captainmaniac · Post by **captainmaniac** » Thu Dec 22, 2011 8:17 pm

Ditto on Paul and Paul's comments... with underwater exhaust you need an above-water relief hole for low speed operation and idling, plus it acts as a tell-tale so you can tell if you are pumping water.

And you want to be careful how far below the hull bottom it hangs down - at speed, there is a LOT of pressure against whatever fittings you might be dragging underneath or behind you. The way that 'fresh air exhaust' looks scares me a bit... that's going to put a HUGE amount of stress on fittings that aren't designed to be yanked on anywhere near that much.

If you look at Paul's design or the 44' you have the pic of, the boot is almost aligned with the hull bottom.

Paul · Post by **Paul** » Thu Dec 22, 2011 8:34 pm

Captainmaniac is correct about the drag created from having it hang down below the hull. To deal with this, I shaped mine like a lower unit at this point to cut thru the water. Also, to attach it to the boat it's bolted at the flange and by an additional bolt at the very bottom of the hull.

g36 · Post by **g36** » Fri Dec 23, 2011 7:49 am

must be the only one but i actually like the sound from my chryslers. i wouldnt want to quiet them down any... interesting stuff

rooferdave · Post by **rooferdave** » Sat Dec 24, 2011 6:48 pm

rbcool wrote:Is that toilet paper coming outta the exhaust??

Ron

actually shrink wrap to deter critters

rooferdave · Post by **rooferdave** » Sat Dec 24, 2011 6:53 pm

captainmaniac wrote:Ditto on Paul and Paul's comments... with underwater exhaust you need an above-water relief hole for low speed operation and idling, plus it acts as a tell-tale so you can tell if you are pumping water.

And you want to be careful how far below the hull bottom it hangs down - at speed, there is a LOT of pressure against whatever fittings you might be dragging underneath or behind you. The way that 'fresh air exhaust' looks scares me a bit... that's going to put a HUGE amount of stress on fittings that aren't designed to be yanked on anywhere near that much.

If you look at Paul's design or the 44' you have the pic of, the boot is almost aligned with the hull bottom.

maybe the pic does not show well but the exhaust I photographed is level with the botom of the hull and is in a streamlined shape, aslo I do not think it has the above water relief. Yet this is a trojan and it is also the same year as mine (76) As I have zero knowledge on the subject all the input is greatly appreciated. I will keep you all up on how it goes and will check before launch