Straight through exhaust

Tamar

Tamar

Well-Known Member
Joined
9 Apr 2019
Messages
7,478
Location
All over the shop
Visit site
My Perkins M30 has the above, the exhaust outlet is on the water line so when I have a few passengers it is below the surface and is quieter.with just me onboard it is very noisy. I want to add a vetus muffler, can anyone see any problems with back pressure when it is under water and has a muffler.
Tia1000026056.png
 
I assume you have a water - injected exhaust, On an earlier boat with a Lister diesel, I fitted a Vetus water lock and a muffler. I subsequently found that the water lock did most of the silencing and I could dispense with the muffler. Perhaps you'd be better off thinking of fitting a water lock if you don't have one already?
 
neil_s said:
I assume you have a water - injected exhaust, On an earlier boat with a Lister diesel, I fitted a Vetus water lock and a muffler. I subsequently found that the water lock did most of the silencing and I could dispense with the muffler. Perhaps you'd be better off thinking of fitting a water lock if you don't have one already?
Click to expand...
Thanks, I did think about the water lock but I picked the muffler up cheap at a boat jumble. Hopefully it will make a difference
 
38mess said:
Thanks, I did think about the water lock but I picked the muffler up cheap at a boat jumble. Hopefully it will make a difference
Click to expand...
It will, but it is not a substitute for a proper waterlock but is an addition. Waterlocks are not expensive. A Vetus to fit yours is under £150.
 
38mess said:
My Perkins M30 has the above, the exhaust outlet is on the water line so when I have a few passengers it is below the surface and is quieter.with just me onboard it is very noisy. I want to add a vetus muffler, can anyone see any problems with back pressure when it is under water and has a muffler.
TiaView attachment 177159
Click to expand...
I fitted one vertical on my 4107 never had any problems and worked well .
 
My boat has a small Beta engine with a waterlock after the engine, a muffler like the above and a Vetus swan-neck thing at the transom.
I don't think back pressure is an issue.

I wonder if the silencing is mostly done by water mixing with the exhaust gases so maybe you might do better with some sort of S-bend before the skin fitting to retain some water in the system?
Do you have a waterlock near the engine?.

I guess your engine is lot bigger than mine and might be flowing a lot more gas at high rpm? Too restrictive an exhaust system might then be an issue, but what I have is pretty common with bigger engines
 
38mess said:
Thanks, I did think about the water lock but I picked the muffler up cheap at a boat jumble. Hopefully it will make a difference
Click to expand...

38mess said:
Thanks, I did think about the water lock but I picked the muffler up cheap at a boat jumble. Hopefully it will make a difference
Click to expand...
Given that the cooling water is driven from the exhaust system by exhaust gas pressure I would carefully do some research to ensure that this silencer doesn’t affect the efficiency of the gas removal, but more important the water ejection
 
Last edited:
I have one of those silencers in my exhaust but I don't think it makes much difference. it the water google that makes most noise so a water Seperator as used on generators may help to lower the noise
 
Beneteau381 said:
Given that the cooling water is driven from the exhaust system by exhaust gas pressure I would carefully do some research to ensure that this silencer doesn’t affect the efficiency of the gas removal
Click to expand...
The ss waterlock box on mine started to leak badly and dump water and exhaust fumes into the bilge.
I had to remove the box for safety (fumes) and connected direct exhaust, it was very noisy (and embarrassing to disturb others when parking or leaving early)
At the time I could only find the vets muffler as above, and decided to fit one, I mounted it vertical above the thro hull outlet so it would drain of any water, a small amount of water was retained in the exhaust 'U' of the Swan neck.
The system worked extremely well, never had a problem and wS quieter than the original watertrap setup. 4107.
 
billskip said:
The ss waterlock box on mine started to leak badly and dump water and exhaust fumes into the bilge.
I had to remove the box for safety (fumes) and connected direct exhaust, it was very noisy (and embarrassing to disturb others when parking or leaving early)
At the time I could only find the vets muffler as above, and decided to fit one, I mounted it vertical above the thro hull outlet so it would drain of any water, a small amount of water was retained in the exhaust 'U' of the Swan neck.
The system worked extremely well, never had a problem and wS quieter than the original watertrap setup. 4107.
Click to expand...
As I said, check carefully, if it goes wrong it means number 3 cylinder fills with water
 
Beneteau381 said:
As I said, check carefully, if it goes wrong it means number 3 cylinder fills with water
Click to expand...
I was running for a while with a blocked exhaust before I discovered the problem and the back pressure was almost popping the rubber end caps off. I must have been extremely lucky not to wreck the engine.
But surely the route of least resistance will be out of the exhaust even with a muffler installed?
 
38mess said:
I was running for a while with a blocked exhaust before I discovered the problem and the back pressure was almost popping the rubber end caps off. I must have been extremely lucky not to wreck the engine.
But surely the route of least resistance will be out of the exhaust even with a muffler installed?
Click to expand...
With the engine running the exhaust pressure would be higher than the water pump pressure at the exhaust port, that said when engine stops any back pressure or water retention could return into a cylinder as at least one exhaust valve will be open. Yours was partial blockage/restricted which gave you the warning indication.
 
I had a vetus muffler on my old boat which I retrofitted to reduce noise. It made a noticeable difference. It wasn't silent but it took the harshness out of the noise. If you already have it from a boat jumble go ahead and fit it. I'm sure it will do the job without any excessive back pressure.
 
38mess said:
I was running for a while with a blocked exhaust before I discovered the problem and the back pressure was almost popping the rubber end caps off. I must have been extremely lucky not to wreck the engine.
But surely the route of least resistance will be out of the exhaust even with a muffler installed?
Click to expand...
The blocked exhaust scenario happened to my mate here in Portugal. I did an article about it two issues ago. It blows coolant out as the seawater pressurises the fresh water system. The exhaust blows the water out, however if the capacity of the system and the height ofthe silencer or pipe is wrong then it all doesn’t get blow out and if the engine is stopped with a full ish system then it can run back in to the exhaust manifold and number 3 cylinder usually cops it. It isnt the pressure needed so much but the capacity of the syste,pm. I am only counselling caution and do some simple volume checks
 
billskip said:
With the engine running the exhaust pressure would be higher than the water pump pressure at the exhaust port, that said when engine stops any back pressure or water retention could return into a cylinder as at least one exhaust valve will be open. Yours was partial blockage/restricted which gave you the warning indication.
Click to expand...

alb40 said:
I had a vetus muffler on my old boat which I retrofitted to reduce noise. It made a noticeable difference. It wasn't silent but it took the harshness out of the noise. If you already have it from a boat jumble go ahead and fit it. I'm sure it will do the job without any excessive back pressurr
Click to expand...
Anyone want to buy a muffler? Going cheap
 
Beneteau381 said:
The blocked exhaust scenario happened to my mate here in Portugal. I did an article about it two issues ago. It blows coolant out as the seawater pressurises the fresh water system. The exhaust blows the water out, however if the capacity of the system and the height ofthe silencer or pipe is wrong then it all doesn’t get blow out and if the engine is stopped with a full ish system then it can run back in to the exhaust manifold and number 3 cylinder usually cops it. It isnt the pressure needed so much but the capacity of the syste,pm. I am only counselling caution and do some simple volume checks
Click to expand...
I know someone who had a waterlock "professionally" fitted to a MD2030. They got it wrong, result was not only a bent conrod on number 3, it actually bent number 2 as well.
 
38mess said:
Anyone want to buy a muffler? Going cheap
Click to expand...
Fit it just before the outlet skin fitting,vertical if possible so it can drain, if the rest of the exhaust is in the same configuration it will work just fine...

But what Ben381 says is correct, which is why I fitted mine vertical so it could drain out. If you don't have the space then go with caution.
 
billskip said:
Fit it just before the outlet skin fitting,vertical if possible so it can drain, if the rest of the exhaust is in the same configuration it will work just fine...

But what Ben381 says is correct, which is why I fitted mine vertical so it could drain out. If you don't have the space then go with caution.
Click to expand...
I have no space under the decks for this. The exhaust just comes out of the engine, drops down about two foot and exits around 4mtrs away in the transom, it been fine for 10 years but I'm getting old now and the noise after a few hours gets a bit much.
 
You must log in or register to reply here.

Share this page

Top