Underwater exhaust conversion...

[Keith-i]

Vas, I fitted a Centek waterlock silencer a while back and iirc the inlet is halfway up the side and the outlet is off the top. Quite what goes on inside I have no idea but I may have a manufacturers diagram somewhere so I’ll take a look for it. I bought a length of 6” grp exhaust tube from asap supplies. I still have a metre spare but I’m not sure of the practicalities of shipping it to you if it would be of use.

 

[MapisM]

Comments appreciated as always

Just a couple of things, V:

1) I don't understand why the blue connecting tube should be so high.
If the purpose is to have the upper part of the box full of water, in order to cool also the higher side of the outlet (diagonal violet tube), I don't think it would work. In fact, unless I'm missing something, the raw water can never go higher than the bottom part of the violet tube, from which it's discharged overboard - in other words, I don't think water would ever reach the upper part of the blue tube, hence possibly leaving all the upper part of the box completely dry.

2) Is it really so difficult to place the final outlet astern?
Aside from being a recipe for having the boat hull always dirty with soot, I don't like the side placement also because whenever the boat should roll with the engines turned off, there is a much higher risk (compared to stern outlets) of water reversal.

 

[vas]

Vas, I fitted a Centek waterlock silencer a while back and iirc the inlet is halfway up the side and the outlet is off the top. Quite what goes on inside I have no idea but I may have a manufacturers diagram somewhere so I’ll take a look for it. I bought a length of 6” grp exhaust tube from asap supplies. I still have a metre spare but I’m not sure of the practicalities of shipping it to you if it would be of use.

thanks Keith,

doubt it makes sense shipping such a thing overseas, especially now that I found a factory building GRP and carbon tubes in various diameters and silly lengths (iirc up to 12m!)
Further, I'm on 5inch, so only use would be for the blue pipe connecting the two compartments that MapisM mentions below.
If you do come across any technical drawing I'd like to have a look, but I doubt they have such things available to customers.

Just a couple of things, V:

1) I don't understand why the blue connecting tube should be so high.
If the purpose is to have the upper part of the box full of water, in order to cool also the higher side of the outlet (diagonal violet tube), I don't think it would work. In fact, unless I'm missing something, the raw water can never go higher than the bottom part of the violet tube, from which it's discharged overboard - in other words, I don't think water would ever reach the upper part of the blue tube, hence possibly leaving all the upper part of the box completely dry.

P., good point, not really much of a reason other that I didn't have time to calculate it carefully and overshot it by maybe 50mm or so
It's like a fountain thing, main idea is getting the water and exhaust make long routes within the silencer thus "reducing" the energy of them, deflecting sound and water all around. You're right the top compartment at most will have 50-80mm of water.
Was also toying with the idea of having a series of holes around the body of this tube for the last 200mm effectively diffusing the water around the top compartment. In a similar manner to the ones used in performance car exhausts (dry of course...)

2) Is it really so difficult to place the final outlet astern?
Aside from being a recipe for having the boat hull always dirty with soot, I don't like the side placement also because whenever the boat should roll with the engines turned off, there is a much higher risk (compared to stern outlets) of water reversal.

outlet astern, just forget it!
the bulkhead separating the e/r to the lazarette features the two 250lt watertanks going all the way to the hull frames and to the salon/aft deck floor. No way in hell I can route a 5+ inch hose there other than to the centre where the e/r access door is, and I'm definitely not doing that :/
Water reversal would at worse (I doubt it will ever happen tbh!) be to the top compartment of the silencer. Top of exhaust riser is a good 500-550mm above the bottom of the side hull exhaust exit.

Did a fair bit of studying and my backup plan is to fit a pressure gauge before the silencer measure back pressure now and then with the thing on at different revs. If it's within specs, I can live with it, especially if it does the job of silencing the IVECOs

cheers

V.

 

[Portofino]

I’d go for a full under water box like on the pics I posted which includes a fart pipe with water .
That fart pipe even though it’s side exit can water wise be only a small out , majority leaving the main box .
For example an oil cooler out so show there’s a flow or a small T , actually a SSteel Y off the main water before .

Use where possible SS piping after your risers .

You see the noise aspect disappears into the expanding gas into the air void at the top of the box and plain seawater .
Once you get Fwds movement and a bit of suction the gas and noise is just dissipated into the sea under the boat .

Those boxes don’t have to be big occupying about 1/2 the space as what you have drawn .
At tick over low rpm use the existing exhaust already in situ for the fart pipe , bit of gas escape , pressure relief and some water to show or hear .Even with full instrumentation you can’t beat the mk1 eye ball and hear .Nothing is more satisfying after a start up is to go to the stern to release the lines and see + hear gas and water exiting - allbeit a token amount.

There’s no bubbles lateral to the UW boxes as the P is too low .
Rev up in N at the dock to 2000 then huge bubbles escape at the lateral aspects .Running you don’t see that .But it’s still quiet exhaust sound wise stationary .

Thing is I,am concerned about the back pressure issue with what you have proposed .Long term not the first 10 mins in the doc or 1/2 hr seatrail before corks start popping deeming it quiet .
Thinking chronic EGT elevation , injector tip hassle , cos it’s too hot in there , hotter than normal downstream turbo blade tips due to gases backing up = bearing failure .

You won’t notice any of this n the first season it will all come home to roost eventually, later .

I know your diagrams are just diagrams but forcing gas through water at different heights all together feels intuitively wrong by guess work .Tick over it might be the worst especially after a run out .No I,am not comfortable with the handling of the back pressure throughout the rev range .

 

[vas]

interesting points Porto and things I'm worried about in general.
However, I have to admit that whatever you typed above also applies to u/w exhaust systems
Further Centek, Halyard and Vetus must have sold thousands of these boxes, wont find much about them causing problems on the internet...

so plan is to:

A. have a modular system built on port engine (three pieces sealed and bolted together)
B. have EGT sensors after the turbo and backpressure sensors after the mixer as well as sw pressure
C. compare B data between the two engines on different conditions.

If port is more than X% or Y value limit (to be debatable) then take the box apart, reduce length of blue tube, or add extra tube connecting top-bottom compartments refit retest. When happy, do stbrd box (next winter...)
if not happy and cannot manage to get it right, dump it and replace with the old exhaust hose which will be stored at the garage at home.
Total loss will be the cost of materials, my labour (that's just fun no loss) and a bit of wear on the keyboard typing all that...
What's not to like?

2X 6+ inch holes at the bottom of my boat is not to be taken lightly (I know I proposed it above...) and the more I think about it the less attractive it becomes especially since there's no drawings/docs/etc explaining and justifying the whole thing. Further if I do the u/w and values on B. above are not right, it means back to the hard for either correction or blanking the holes...

cheers

V.

 

[vas]

this cutout is the clearest i've found demonstrating the way these things are meant to work.
No reason to believe that actual boxes by Vetus are much different inside than this!

 

[vas]

and an interesting take on underwater exhaust, tempting, v.tempting!
only problem I see with this is that the 5inch exhaust hose from the mixer will be "flying" fairly high to enter this box way above w/l which means access to the outside of the engine will be "interesting" having to crawl under it, not going to be fun...

[from http://www.cottyfaymarine.com]

 

[MapisM]

V, I'm struggling a bit to understand the constraints of your e/r.
Do you possibly have a drawing of your current exhaust system, or maybe a pic?
An indication of the static w/l would also be interesting.

 

[vas]

sorry P.

thought I had a couple of pics posted in this thread, alas...

static w/l is fairly low say 150mm (more likely 200mm) lower than the low point in the flexhose to hull side outlet.

[excuse the mess...]

V.

 

[MapisM]

Interesting. I didn't realize/remember that the OEM exhaust is straight out to the boat sides.
Are you really sure that you can't live with the noise?
From the engines efficiency/health viewpoint, Versilcraft made those exhaust precisely "comme il faut", I reckon!

 

[vas]

well, I guess the other similar sized (or slightly bigger) Versilcrafts must be straight out to the grp (the only grp piece of the whole boat btw!) scoops on the sides.

and to answer the main Q, yes, it's getting on my nerves after a couple of hours even at 7 or 8kn. It's ok(ish) on the f/b but none can sit and have discussion on the aft deck and usually the ladies are there. Kids are either inside or at the bow (and generally don't mind that much although daughter has complained a few times)

Well whatever I do I now have all the kit to measure and compare port to stbrd re EGT, backpressure after the riser or at the EGT probe position 100mm after the turbo as well as the seawater circuit pressure before the heat exchangers.
If ALL these values are identical and backpressure is within IVECOs specs I'll be happy.

BTW, I just came across these guys who seem to have some interesting designs for u/w exhaust. Have a look at the following pages:

https://www.vonwidmanndesigns1.com/recent-works

interesting idea with running the exhaust in parallel to the hull going aft to cool the exhaust mix before going up and out to create the necessary suction/bernouli on the way out. Very smart!
https://www.vonwidmanndesigns1.com/single-post/2019/03/21/Have-not-seen-you


cheers

V.

 

[Portofino]

I’ve nicked a pic from above .
You need just the box bit with main gas / water entering from above and a smaller water in ( say from oil cooler ?) to the side or use existing rear pods as fart pipes .

The red box is an additional silencer really just a Kellogg box size expansion chamber to lower the noise more in the fart pipe .
That side gas out will control back pressure below rpms to overcome the head / depth of water and relative lack of suction at slow speeds .

This is essentially what I have except a little underwater sculpture.
- a fwd deflector
- rear of the box it’s slight ramp so sort of increases the mixture area like the above a little .

WL is where I put the blue line - more / less same as mine .

Obviously my fart pipes are through to the rear 1/4 s and there’s a grp glassed in box say rectangle 70 cm x 15 x15 before the SS outlets .

Zero exhaust noise basically in the boat .

 

[vas]

boat is still in the water, and I'm still considering options re exhausts.

Finally yesterday evening I had a go at 3D modelling in AutoCAD an underwater exhaust option.
The idea is that there'll be a ply/epoxy/mat box approx 400X210X300mm (LxWxH) with a SS "lid" where the 127mm dia exhaust pipe will be coming in.
There's going to be a 2.5in fart pipe which will be functioning in the way the single chamber vertical mufflers work.
An oval (anyway some short of shape...) hole will be passing the main bulk of the water/gasses to a reasonably streamlined chamber which is open to the sea.

Idea is that since up to around 8kn the demand is for 40-45hp from each engine. So up to low D speeds this design I believe would facilitate venting all gasses/water through the bypass/fart pipe which will simply go into the 127mm hole on the side of the hull.

Thinking about it after finishing the model, I'd probably lift the sides to the hull side up to the main box height, which means that even if something is messed up and there's a leak on the final outlet area/shapes, water will be contained in there and in theory I should be able to go slowly back to port or wherever safe.

So in a way this is a 2 in 1 solution with underwater exhaust, plus a one chamber muffler (with a twist) running the fart pipe and quieten things on the way out.
Note that there's a small(ish) inlet ramp and the outlet has a 20deg rise (IIRC, could be 24) to help in venting gasses and water to the sea when the boat is moving.

any ideas welcomed

V.

 

[vas]

morning all, an update!

after lots of back and forth, sketches, more sketches and lots of measuring I decided to go for it.
I minimised the whole setup and pushed it as far outwards as it can posibly go. So now its a box 380X140X360mm (outside dims) sitting just under the existing side outlet with a slot to let the gasses/water combo exit under the craft by the chine.
Slot is 330mm long, average 100mm wide and the narrower part of it at the back is slanting upwards to let gasses exit more gracefully when boat is moving. There's going to be a deflector on the front side as well. Actual hole is going to be approx 25% larger in surface than the 127mm dia exhaust hose, so there shouldn't be a bottleneck there.
Further, the lid (not seen in the pics below as it's not even made yet...) will be ss and will have a SS elbow parallel and to the side of the existing exit. Means swapping from my box to original outlet will be 5min job (with engine cool ) The lid will also have a 45mm dia outlet going around 50mm lower than the w/l so that it will pick water and some gasses as and when needed from the box to the side original outlet. Fart pipe of a silencer sort of thing.
Telltale pipe would have to come from the stuffing box water will devise something at some point. After all I've got my seawater circuit pressure to give me a warning if there's a blockage/whatever in the seawater cooling circuit.

Regarding the box construction, it's 18mm marine ply (yes it's thick...), which on Tue will be epoxied and bolted on the frames and with 40x40mm battens secured all around where there's no iroko frames to keep it contained (ie. the free side towards the centre of the boat) There's going to be another 40X40 all around the top to give enough surface to seal the ss lid on. Then George is doing some triangular section 30X30mm pieces to "break" the corners so that I can start glassing and epoxying the boxes inside. Would like to have a fairly decent thickness of glassfibre there, maybe 3 layers, we shall see.
There will be close spaced through bolts with nuts embedded on the other side of the battens and probably some sika in between (will try a foamy rubber strip not sure on temp rating though-will see)
Box volume is not v.large, water line is approx 150mm down from the lid, so plenty of "breathing" space in there. May end up adding a baffle in the lid going under the waterline to deflect further the gasses, lower their energy and silence it a bit more.
Slightly worried if I'm buidling a nice marine home in there, will make sure everything is smooth and sloping downwards!

Some pics for now:

test fitting the pieces (need cutting on top to level them with the back reinforcing panel):

the free standing piece will pierce through the hull and create a small (say 25mm) deflector sending the gasses/water combo outwards and away from the props (it's far away as it stands anyway!) BTW, I know that I should really have the trapezoid shaped hole opening up at the back but would either have to weaken the 32mm iroko beam on the chine side which I don't want to , or sent more gasses towards the props which I also don't want to...

and how the thing looks from outside (just drilled the corners and drawn the box, will cut on Tue.

Plan is to finish off the two boxes, antifoul the area around (had left the top chine with the old non-functioning copper epoxy a/f when I did coppercoat the rest of the hull) and be in the water next w/e. We shall see

cheers

V.

 

[MapisM]

Vas, if anyone else would be doing what you are doing, the more polite comment I could think of (noise reduction aside) is that such job will at best affect negatively the engines efficiency, and at worst could be downright dangerous for the vessel safety.
Then again, it's not anyone else who is doing that, it's your good self......
I wish you all the very best for the first sea trial, I for one am really looking forward to read about it.

 

[Bouba]

Amen to that. Vas, I would never judge you because I mostly can’t understand you. But have you tried the simple approach first, like sound insulate your engine room?
Please feel free to disregard this

 

[vas]

Vas, if anyone else would be doing what you are doing, the more polite comment I could think of (noise reduction aside) is that such job will at best affect negatively the engines efficiency, and at worst could be downright dangerous for the vessel safety.
Then again, it's not anyone else who is doing that, it's your good self......
I wish you all the very best for the first sea trial, I for one am really looking forward to read about it.

P.,

worries accepted, only with all the sensors installed it's highly unlikely the engines will have a chance to be damaged... If values escalate (EGT-backpressure) I'll just pull back the levers and next morning with engines cool I'll swap the exhaust flex hose from the custom box to the original side outlets. Even had a crazier idea of using the box as a silencer without a bottom and get a second 127mm dia elbow facing the side outlet, effectively use a fartpipe the same dim as the normal exhaust Easy to do with Nikos (the ss fabricator) if things don't pan out right. TBH, I very much doubt I'll notice anything abnormal with the 45mm fartpipe.

Amen to that. Vas, I would never judge you because I mostly can’t understand you. But have you tried the simple approach first, like sound insulate your engine room?
Please feel free to disregard this

damn Bouba, I thought my english was good enough for the natives to understand
yep, e/r is now fully soundproofed with v.decent (and bloody expensive!) material and an lead based undercarpet material is also in place keeping the noise from the engines at v.decent levels in the salon. The problem is the booming and general exhaust noise when sitting on the aft deck, doing your head in.

cheers

V.

 

[MapisM]

Even had a crazier idea of using the box as a silencer without a bottom and get a second 127mm dia elbow facing the side outlet, effectively use a fartpipe the same dim as the normal exhaust

I see the rationale of that, but don't forget that u/w exhausts, if well designed, can also INCREASE the engines efficiency, and with this solution you couldn't exploit this potential advantage. I appreciate that I am now contradicting my previous post, sort of, but bear with me.

Depending on the placement and design of the outlets, and obviously also on the boat speed, you can create a scavenging effect, reducing the backpressure even in comparison to straight exhausts, in turn lowering also the EGT.
Now, according to the initial seatrial report of my boat, backpressure is very low at idle (courtesy of the bypass), but rapidly increases from 900 to 1600 rpm, because this is the range where the bypass struggles to cope with the higher exhaust flow, and the boat is not yet fast enough to create a scavenging effect on the u/w outlet.
But after 1600rpm, backpressure suddenly drops by almost 50%, and stays constant all the way up to WOT - unsurprisingly, since 1600rpm is when the hull begins to be steadily on the plane.

Bottom line, on P boats, u/w exhausts can be not only effective for reducing noise, but also for improving the boat efficiency/performance.
But AFAIK, their design and position is carefully considered from the beginning, at hull design stage.
And afterwards, checked and possibly adjusted based on the initial results with boat #1.
More easily said than done, when retrofitting...

 

[vas]

P,

all's fine, except that i'll be using my engines (well, I AM using my engines) at around 1300rpm 7-8kn. So that's the max backpressure I'll get I guess.
anyway next Tue MiToS will be back in the water and testing will commence
for the time I'm on two saunas a day (morning and worse evening) with ambients from 32-38, not nice working in the e/r and climbing up and down all the time, I'm getting old (and tired!)

holes cut, pieces matched and epoxied in place. Battens also epoxied and bolted in place, whole box looks overengineered tbh. Tomorrow I'm getting the 4mm SS lid and matching the elbow for the exhaust pipe.
BTW, anyone aware that the 127dia exhaust hose (5in for you up north) is actually 129mm???
Nikos the fabricator had a 129mm OD ss pipe that was going to use and was not particularly keen that he had to cut it, remove some material (probably just over the width of the cut) and weld it again to drop it down to 127mm. Only to take the port hose (it's shorter...) over to his workshop for testing to find out that it fits fine without messing about!
Checking back on the boat, sure enough the factory fitted hose is 129mm OD, odd?

anyway, the hole:

still missing the deflector in the front, done but not epoxied yet:

and the overengineered box from the inside, no way in hell this is going to be compromised and boat flooded through here!

cheers

V.

 

[Mr Googler]

As said.....anyone else....this would be madness but Vas....you’re a genius!