wet exhaust/muffler Volvo MD

[Neeves]

We have what I think is called a 'wet exhaust', which is now leaking. These are standard Volvo components.

It is located prior to the water exit from the yacht, prior to an anti syphon loop and after the exhaust elbow. It consists, from the exterior, of a rubber cylinder with 2 stainless end pieces that take the exhaust and sea water hose. The rubber cylinder is clamped to the stainless end pieces with large hose clips, 2 at each end.

I understand the cylinder or reservoir muffles sound and holds water that runs back from the hoses, so they cannot flood the engine.

Ours are 16 years old - so difficult to complain about lifespan. But the one that is leaking is where the stainless has corroded at the bottom of one end piece, not at the weld. It seems to have corroded as it has always had seawater in contact for 16 years.

Do they need to be made from stainless? The water at that point is hardly 'hot' why not make them from fibreglass (they might then last, even, longer and could more easily be repaired). I have not taken ours apart - is there anything sophisticated inside the cylinder?

Jonathan

 

[macd]

Yes: no need for stainless. They're most commonly made from plastic and have been for years. GRP is also used, although lends itself less well to volume manufacture. They're usually called a water trap, but have some silencing properties. The Vetus catalogue is full of them, and of schematics of 'correct' exhaust design, such as here: http://www.vetus.com/exhaust-systems/waterlock-muffler.html

The interior design isn't complicated, but it does need to be right.

The "anti-siphon" you mention is probably not: it' sounds more like a goose-neck/swan-neck, to deter ingress of water from the sea. An anti-siphon, of course, would have an air bleed facility at the top of the loop; a goose-neck does not. Anti-siphons are intended to prevent siphoning on the inlet side and are thus located at some point between the seawater pump and the mixing point at the exhaust elbow, but most commonly after the heat exchanger.

 

[Neeves]

Thanks Mac, we live and learn.

We actually have 2 anti syphons, both have bleed facilities, one on the exhaust (as mentioned) and one on the seawater intake side, post impellor but prior heat exchanger.

I'll have a look at Vetus (I had only thought of Volvo, Vetus are not mainstream in Oz)

Jonathan

 

[DownWest]

Inside there is a baffle at the forward end and the aft exit tube is turned down inside to close to the bottom. This ensures that the exhaust gas pressure blows out any water that drains down from the tubing further aft.

The one I looked at was also leaking, but from the drain plug at the aft end. Instead of the original ss plug, there was a brass one and it had disintergrated from galvanic corrosion.

I replaced it with a GRP custom made one as it was not big enough to contain all the drain-down water. I think that surging from punching into head seas was the cause of sea water getting into the engine requiring rebuilds. Since I could not find a Vetus one that was big enough and would fit in the space, the GRP one built.
Vetus also make mufflers as seperate items.

One plus of GRP, is that in the event of a raw water pump failure, it lasts longer that the moulded plastic ones in the hot gas.

Edit: Neeves, I was typing (slowly..)while you were replying. The unit could have been repaired with a patch, but it was not the problem. It was just not big enough. Forgot to mention too, that it had a temp sensor at the forward end to warn of pump failure. This might be a good idea as you go forward.
Andrew

 

[youen]

Had the same problèm on my Volvo waterlock after only 6 years the stainless steel was totally corroded by the mix saltwater and gas inflortunatly I had not enough room to put a Vêtus one

 

[macd]

Jonathan: I've edited my post for clarity since (I think) you read it.

I'd agree with DownWest that a temp alarm is worth considering since the exahust hose, if not your steel water-trap, is very vulnerable to prolonged dry running. You can pay a small fortune for a proprietory one, but a temperature-sensitive switch and a buzzer cost just a few $ and do the job just as well. Locate it* at the bottom end of the mixing elbow, below the water injection point. The normal running temperature there is surprisingly low, so spec the switch for something like 70C.

* the switch, not the buzzer :ambivalence:

 

[youen]

Did the same bought one exhaust temperature alarm very easy to mount from Salty John (no link)

 

[charles_reed]

We have what I think is called a 'wet exhaust', which is now leaking. These are standard Volvo components.

It is located prior to the water exit from the yacht, prior to an anti syphon loop and after the exhaust elbow. It consists, from the exterior, of a rubber cylinder with 2 stainless end pieces that take the exhaust and sea water hose. The rubber cylinder is clamped to the stainless end pieces with large hose clips, 2 at each end.

I understand the cylinder or reservoir muffles sound and holds water that runs back from the hoses, so they cannot flood the engine.

Ours are 16 years old - so difficult to complain about lifespan. But the one that is leaking is where the stainless has corroded at the bottom of one end piece, not at the weld. It seems to have corroded as it has always had seawater in contact for 16 years.

Do they need to be made from stainless? The water at that point is hardly 'hot' why not make them from fibreglass (they might then last, even, longer and could more easily be repaired). I have not taken ours apart - is there anything sophisticated inside the cylinder?

Jonathan

Mine is 26 years old and a plastic one made by Vetus - it' on its second engine and third lot of exhaust tubing.
I tend to avoid anything made by Volvo - looking suspiciously for their deliberate design mistake, rather than their excessive margins.
Apart from Vetus, give Halyard Marine, here in the UK a ring and "discuss" their pricing. Usually I've found them very "sensible", though I had an awful experience with a prop-seal they produced (and withdrew) which put me on the moral high ground.
Most mufflers are in hellish inaccessible positions and inadequate space so I wish you luck (and the services of a treble jointed, extra-long armed achrondoplast.
Re sophistication - entry above exit and, ideally, @ or above waterline, below exhaust elbow. They actually mix water and gases rather than prevent backflow, talk to a competent marine engineer or naval architect.
It's amazing how quickly a faulty exhaust-line or failed raw-water pipe fills a bilge!!!
So do it quickly.

 

[ghostlymoron]

My MD1 had a modified exhaust system. The Volvo muffler was removed and replaced with a Vetus water trap to stop exhausted water running back into the engine when it stops, and a gooseneck from the same supplier. Both are made from plastic and good quality but expensive. There are many patterns of inlet/outlet to fit in awkward spaces. The trap needs to have enough volume to hold all water contained in the exhaust line to the outlet.

 

[Neeves]

Charles you must have seen our engine bay - you have described it perfectly. We actually have plenty of room for a big muffler - but then there would be no room for scrunched up me! Mac, I've taken note of the corrections or changes. My first line of investigation will be Vetus who appear to have a consistently positive following, on this thread (and who gave me good service with their windlass).

We unfortunately discovered how quickly the failed muffler fills the engine bay up with water. Coincidentally we were monitoring the heat exchanger, that I had sand blasted and I had just installed with a new thermostatic valve - or we would have had more water in there. A slow drip becomes a veritable deluge when the engine is running - its amazing the amount of water we collected and so quickly.

I'll have a look at a temperature alarm as well.

Thanks for the informed and consistent comments. Its nice when everyone agrees!

Jonathan

 

[macd]

The trap needs to have enough volume to hold all water contained in the exhaust line to the outlet.

To elaborate a little (but keeping everything 'nice' as Jonathan mentions :encouragement Vetus state that the maximum volume of water in the exhaust when an engine is running is 25% of total exhaust volume. They then add a safety factor and advise that the water trap should be sized safely to hold 50% of exhaust volume. They even have a little volume calculator somewhere on their site, although there are plenty of hose (i.e cylinder) calculators on-line if you prefer to check it yourself. Or do it the old way with Πr² x length.

 

[Neeves]

Having perused the Vetus catalogue I find our Volvo 'waterlock/muffler' looks antediluvian and crude. Vetus having nothing like it. I would be spoilt for choice - except I find, prompted by ghostlymoron and Mac, that there is science behind choice and I need to measure my exhaust plumbing and polish up my arithmetic - as I have learnt not to assume the installation we have is correct.

Jonathan

 

[DownWest]

Having perused the Vetus catalogue I find our Volvo 'waterlock/muffler' looks antediluvian and crude. Vetus having nothing like it.
Jonathan

They still sell them though...

One point about volume is that because of the Volvo design, with the inlet and outlet inline with the main chamber, the water capacity is around half of the total volume, part of the problem on the installation I was looking at. Vetus has the ports above the main body, allowing better use of the 'tank'. Because of the history of water getting back to the engine, I used as much of the limited space as possible to cater for the total volume of the exhaust piping and swan neck. Belt and braces after one rebuild and one new engine....
DW

 

[Tranona]

The Vetus NLP3 is a good replacement for the Volvo muffler. 5l capacity is enough for a 2020 engine unless you have a superlong exhaust - I am guessing your exhaust is even shorter than a typical mono. The pot type NLP is also suitable, but being a different shape may not fit your space. Halyard Marine also have a GRP one that would be a replacement.

Unlike others I have had good service out of the Volvo muffler. My 2001 Bav 37 is still on its original one with no signs of corrosion.

 

[Neeves]

Tranona, you have a good memory - our pipe runs are very short. This engine is located back to front, engine aft of the saildrive so the exhaust elbow faces forward. The muffler is located 'alongside' the raw water pump, just behind it (so right aft), and the pipe run is from the elbow round the engine to the muffler, then a loop up to the deck and back to, the hull fitting, just above waterline. So very short, though lengths are very deceptive - its not far but the pipe work makes lazy curves - being stiff. I'm off to measure up today.

Our muffler is just a bit older then yours and maybe warmer weather increases corrosion. But I'm not complaining - 16 year life of a marine component is better than the life of many components.

I am surprised that given the acceptability of plastic, which surely might last longer, its not used as standard.

I also note that the Vetus mufflers have a drain port for winterisation, missing from the Volvo. This suggests that Vetus are possibly considering frost but Volvo allow water to sit there 365, corrosion - and frost or not. I don't see how you can easily drain a Volvo muffler without disconnecting the pipework. We don't winterise here, I suspect 'winterise' is not in the Australian dictionary, but draining of the exhaust system is not something I recall enjoying much emphasis on any PBO et al winterisation schedule.

Mention has been made of a thermostat alarm - I note Vetus sell one and it reads as if they incorporate a port (or a simple cut out) to accomodate the thermostat in their mufflers.

Jonathan

 

[Tranona]

Very little water ends up in the muffler and it is very shallow so there is really no need to drain it to protect from frost. The Vetus type is much deeper and the plastic can potentially crack if the water freezes - hence the drain.

Like all things there are staunch advocates of different solutions. I used to be very friendly with a salesman for Halyard who would tell tales of doom and gloom if you used plastic waterlocks - but of course he sold GRP ones! The Volvo type is an exercise in extreme simplicity and thousands are in service with few problems. I have owned both types and had no problems with either. However, if I was lucky enough to own one of those fabulous big MOBOs so loved by some of the folks on the MOBO forum, I would expect only GRP waterlocks! BTW when the idea first came in they were usually fabricated from stainless steel - or even mild steel and it took only a few years to find out how unsatisfactory they were and how quickly the Vetus type took a big share of the market.

 

[prv]

I am surprised that given the acceptability of plastic, which surely might last longer, its not used as standard.

Well, it is pretty standard. I've only come across plastic ones in person, I've heard of GRP, but stainless steel and rubber is a new one on me

Pete

 

[Tranona]

Well, it is pretty standard. I've only come across plastic ones in person, I've heard of GRP, but stainless steel and rubber is a new one on me

Pete

Standard equipment on thousands of Bavarias (and Volvo engined HRs). Given the number in use and the fact you as a regular poster here have never heard of them suggests they are pretty trouble free. In fact even on Nigel's Bavaria forum I think I have only seen one thread on the subject.

 

[scottie]

Volvo rightly or wrong have thought outside of the box in many occasion either by designing their own or outsourcing
Saildrives and combined rubber shaft seals are two of the better ones that come to mind
Self erasing hour meters from VDO whilst a great source of income for their spares dept one of the worst

 

[pvb]

Standard equipment on thousands of Bavarias (and Volvo engined HRs). Given the number in use and the fact you as a regular poster here have never heard of them suggests they are pretty trouble free. In fact even on Nigel's Bavaria forum I think I have only seen one thread on the subject.

My old HR352 had a Volvo stainless/rubber muffler, fitted in 1990 when the boat was built. It was still working fine in 2014 when I sold the boat.