Water up exhaust

jonathanhsm

Member
Joined
8 Jan 2007
Messages
192
Location
Lymington
Visit site
Went for a long run – messed about for ages trying to pick up a mooring – secured then turned off engine. When I tried to restart a few minutes later there was a dull klunk – motor refused to turn over. This had happened once before when water had found itself into the cylinder(s) via the exhaust. So this time I immediately checked the exhaust water trap which was full up. As soon as I drained it the engine turned over and started.
The first time this happened I assumed that waves had forced water up the exhaust. This time though there was little swell. So I can only assume water in the gooseneck to the exhaust had gone back to the trap which filled up and pushed water through exhaust outlet into cylinder. But why has it only happened twice ? So what’s the solution – a bigger trap?
The first time it happened I took out all the injectors got all water out etc. This time once trap was emptied the engine turned and started. I kept it going for half an hour so hopefully will be OK? I don’t really want it to happen again so any advice gratefully received. PS engine is a Perkins Perama M20 almost identical to Volvo md2020. Exhaust goes down into water trap and then up (as high as cockpit sole will allow) into a loop then down to exhaust outlet which discharges vertically from stern which is swept up and clear of water – but only by a couple of feet or so. There is an anti-siphon valve - which has been blocked in the past - could this have caused the problem?
 

sailorman

Well-known member
Joined
21 May 2003
Messages
78,860
Location
Here or thertemp ashore
Visit site
Went for a long run – messed about for ages trying to pick up a mooring – secured then turned off engine. When I tried to restart a few minutes later there was a dull klunk – motor refused to turn over. This had happened once before when water had found itself into the cylinder(s) via the exhaust. So this time I immediately checked the exhaust water trap which was full up. As soon as I drained it the engine turned over and started.
The first time this happened I assumed that waves had forced water up the exhaust. This time though there was little swell. So I can only assume water in the gooseneck to the exhaust had gone back to the trap which filled up and pushed water through exhaust outlet into cylinder. But why has it only happened twice ? So what’s the solution – a bigger trap?
The first time it happened I took out all the injectors got all water out etc. This time once trap was emptied the engine turned and started. I kept it going for half an hour so hopefully will be OK? I don’t really want it to happen again so any advice gratefully received. PS engine is a Perkins Perama M20 almost identical to Volvo md2020. Exhaust goes down into water trap and then up (as high as cockpit sole will allow) into a loop then down to exhaust outlet which discharges vertically from stern which is swept up and clear of water – but only by a couple of feet or so. There is an anti-siphon valve - which has been blocked in the past - could this have caused the problem?

the exhaust must have a large loop before the skin fitting.
(the Vetus site has a good diagram / schematic layout)
the vent is extremely important to stop the cylinders sucking in water, the Vetus site also gives dimensions for this as well
 

Chris_Robb

Well-known member
Joined
15 Jun 2001
Messages
8,054
Location
Haslemere/ Leros
Visit site
Went for a long run – messed about for ages trying to pick up a mooring – secured then turned off engine. When I tried to restart a few minutes later there was a dull klunk – motor refused to turn over. This had happened once before when water had found itself into the cylinder(s) via the exhaust. So this time I immediately checked the exhaust water trap which was full up. As soon as I drained it the engine turned over and started.
The first time this happened I assumed that waves had forced water up the exhaust. This time though there was little swell. So I can only assume water in the gooseneck to the exhaust had gone back to the trap which filled up and pushed water through exhaust outlet into cylinder. But why has it only happened twice ? So what’s the solution – a bigger trap?
The first time it happened I took out all the injectors got all water out etc. This time once trap was emptied the engine turned and started. I kept it going for half an hour so hopefully will be OK? I don’t really want it to happen again so any advice gratefully received. PS engine is a Perkins Perama M20 almost identical to Volvo md2020. Exhaust goes down into water trap and then up (as high as cockpit sole will allow) into a loop then down to exhaust outlet which discharges vertically from stern which is swept up and clear of water – but only by a couple of feet or so. There is an anti-siphon valve - which has been blocked in the past - could this have caused the problem?

There is one very silly possibility which I have seen before. The trap can be connected in the wrong way with the exit connected to the engine side and vice versa. The exit has a dip tube in it, which means the water is scavenged to the bottom of the tube, and so there is enough volume left for the drain back from the exhaust.

It could also be that your dip tube has broken off.

Worth checking anyway to eliminate this.

Also worth checking the antisiphon valve as a combination of the above and this would definitely cause a problem.
 

PetiteFleur

Well-known member
Joined
29 Feb 2008
Messages
5,043
Location
Suffolk
Visit site
On a previous boat I also had a Perkins M20 with a stainless water trap and then the exhaust pipe went into a high loop against the transom before exiting at just above water level. Must admit I never had a problem with water filling up the water trap but I did have a siphon trap fitted. (but the Exhaust Elbow coked up and was renewed with the VP one which was identical and cheaper!)
My current boat with a new engine I fitted all Vetus gear, a water trap, inline muffler and gooseneck on the transom. I did redirect the exhaust through the transom rather than underwater as the original installation. And I fitted a syphon trap which is the open type which piddles water out through the transom. This I converted as the original syphon salted up after a season.
 

CSFenwick

New member
Joined
7 Mar 2005
Messages
250
Location
Cheshire
Visit site
From your description the exhaust outlet was well above the level of any lapping water implying the water hadn't come back up the exhaust from the sea. Meaning it's cooling water coming from the heat exchanger. Is it possible that the exhaust is becoming blocked? - build up of carbon? So at idle (picking up mooring) it isn't quite clearing the lift box which slowly fills up? I don't know your specific engine but assuming you have an injection elbow I'd take that off and check it's not becoming blocked.

On our Perkins M50 the elbow was getting choked with carbon specifically at the point the raw water joined resulting in over pressure in the raw water circuit and raw water being pushed past the seal into the fresh side. Not your problem but if the restriction is further down...

Worth a look anyway.
 

VicS

Well-known member
Joined
13 Jul 2002
Messages
48,364
Visit site
There is an anti-siphon valve - which has been blocked in the past - could this have caused the problem?
Thats is one of the first things I would check but I'd not expect it to fill the system in a few minutes unless the injection point into the exhaust is well below the water line level and the pump impeller getting a bit worn
 

conor54

Member
Joined
21 May 2010
Messages
42
Location
Ireland
Visit site
Hi,

I have a Perkins Permama M20 in a Contessa 32. A few seasons ago my engine began to get harder and harder to start and got water back up in the exhaust as far as the engine block. Like you I then had to drain the water lock before trying to start again. I think the original problem was that the waterlock was not low enough and on one tack it could empty its water into the engine. Sometimes this would all drain back to the waterlock when the boat levelled out but sometimes not.

It got to the point where I would close the seacock before pulling the stop to try to keep the waterlock mostly empty when the engine was not running. I would also start the engine before opening the raw water seacock as sometimes it would crank but not fire but was putting water into the waterlock. Possibly this water in the waterlock + a short run of hose meant that there was too much back pressure - not really sure.

However some damage was done and I had to get the engine expensively rebuilt. There was a lot of pitting on the rearmost(lowest) cylinder head from the water.

After the rebuild I wanted to prevent a re-occurence so I changed the exhaust around. I got a local firm to make up a stainless riser and fitted a 10 litre vetus waterlock box. The engine now starts far more easily that it did with rebuilt engine+old exhaust setup.

There are some pictures of my solution here:
https://picasaweb.google.com/114505843350208459584/Contessa32Exhaust#

All the best,

Conor
 

PetiteFleur

Well-known member
Joined
29 Feb 2008
Messages
5,043
Location
Suffolk
Visit site
Hi,

I have a Perkins Permama M20 in a Contessa 32. A few seasons ago my engine began to get harder and harder to start and got water back up in the exhaust as far as the engine block. Like you I then had to drain the water lock before trying to start again. I think the original problem was that the waterlock was not low enough and on one tack it could empty its water into the engine. Sometimes this would all drain back to the waterlock when the boat levelled out but sometimes not.

It got to the point where I would close the seacock before pulling the stop to try to keep the waterlock mostly empty when the engine was not running. I would also start the engine before opening the raw water seacock as sometimes it would crank but not fire but was putting water into the waterlock. Possibly this water in the waterlock + a short run of hose meant that there was too much back pressure - not really sure.

However some damage was done and I had to get the engine expensively rebuilt. There was a lot of pitting on the rearmost(lowest) cylinder head from the water.

After the rebuild I wanted to prevent a re-occurence so I changed the exhaust around. I got a local firm to make up a stainless riser and fitted a 10 litre vetus waterlock box. The engine now starts far more easily that it did with rebuilt engine+old exhaust setup.

There are some pictures of my solution here:
https://picasaweb.google.com/114505843350208459584/Contessa32Exhaust#

All the best,

Conor
After I initially fitted my Beta 25 engine, I realised that the standard exhaust was barely higher than the waterlock so fitted a High Rise version which Beta swopped for the original + ££ and it has worked well.
 

jonathanhsm

Member
Joined
8 Jan 2007
Messages
192
Location
Lymington
Visit site
Thanks all. My system looks very much like Conor's "old" system. And I think the problem has probably been there for some time. When I got the boat the exhaust valve on cylinder next to exhaust elbow was rusted in and broke the rocker in mid Solent. Anyway I fixed that - and hopefully recent experience won't have caused a problem as the engine was up and running within ten minutes of "seizure" so hopefully no time for corrosion. I like the solution but not sure I want to spend too much money right now. I am hoping it is down to the anti-siphon valve being crudded which would explain the fact that it has happened only twice (in my ownership) in scores of engine starts. One of my boating colleagues suggested that if the siphon was blocked then water could be "sucked up" into exhaust as engine cooled? Although I'm no expert on hydrostatics!
 

Tranona

Well-known member
Joined
10 Nov 2007
Messages
41,490
Visit site
Thanks all. My system looks very much like Conor's "old" system.

In which case you are never going to be able to solve the problem. The Vetus instructions are quite clear - min 30cm from water injection point to inlet to water trap. If the hull is not deep enough to achieve this then you need a high rise exhaust manifold to raise the injection point.
 
Joined
26 Nov 2009
Messages
13,406
Location
everywhere
Visit site
If the anti syphon valve is blocked you could well get water syphoning into the exhaust via the pump and heat exchanger - depending on relative levels of course. But if a blocked anti syphon valve didnt allow that then you have to ask what the valve is there for.
 
D

Deleted member 36384

Guest
From this web site http://www.tb-training.co.uk/Exhaust.htm :-

Water filling the exhaust from the raw water system

Although the raw water pump should not pass water when it is stationary it will almost certainly do so as it or the impeller wears. This will allow raw water to fill the exhaust pipe and back-feed into the manifold and engine. To guard against this at some point the supply from the raw water pump should be taken through a high swan neck that is well above the waterline. The top of this swan neck should be fitted with a siphon break valve at the highest point.

I believe that what he is saying is that when the engine is off, a worn pump will allow seawater to bypass and fill the exhaust. This could be another area to check.
 

VicS

Well-known member
Joined
13 Jul 2002
Messages
48,364
Visit site
These two pictures below from Vetus show how an antisyphon valve should be plumbed in to the system. Two types are shown one with a valve that opens to admit air, the other with a vent tube but no valve that can either discharge a continuous stream of water overboard or into a cockpit drain where it can be seen. ( these are the old types, Vetus have changed the design a bit now)

The waterlock trap must be large enough to easily hold all the water which remains in the exhaust system when the engine is shut down.



VetusV.jpg


VetusH.jpg
 
Top