Exhaust Riser needed.

[jonathanhsm]

Checked boat after recent storms on exposed mooring. Water up the exhaust had got to the cylinders presumably forced up the exhaust pipe which points straight down underneath transom.- filling water trap to brim and then onwards to manifold. So when trying to start hydrauliced immediately; Normally stick a tennis ball up the exhaust but this usually falls out. Managed to get water out by taking out injectors and spinning engine, and lo it started fine after that. Hopefully no damage done. However this isn't the first time this has happened and looking for a permanent solution. There is a working anti-siphon valve in place over the raw water inlet so water is not coming from there - in any case I always close the inlet seacock. The problem is that the drop from the exhaust water injection point to the water trap is minimal and there's no room to increase the angle. As an interim I will fit a valve on the 50mm exhaust pipe and hopefully remember to turn it off and on. But ultimately need an exhaust riser. Does anyone manufacture such things? Engine is Perama 18hp M20 - almost identical to Volvo 2020

 

[TopDonkey]

How about fitting a suitably sized one of these ?

http://www.ebay.co.uk/itm/4-inch-rubber-exhaust-flap-/160721108335?pt=UK_CarsParts_Vehicles_BoatEquipment_Accessories_SM&hash=item256bb97d6f#ht_500wt_1361

 

[jonathanhsm]

How about fitting a suitably sized one of these ?

http://www.ebay.co.uk/itm/4-inch-rubber-exhaust-flap-/160721108335?pt=UK_CarsParts_Vehicles_BoatEquipment_Accessories_SM&hash=item256bb97d6f#ht_500wt_1361

Good thought I didn't even know these existed - my exhaust points vertically down - would this still work?

 

[VicS]

Can you not fit a swan neck in the exhaust before the final discharge. Either something like the Vetus one or simply by taking the hose, after the water trap, up in a loop to deck level before coming back down to the outlet.

 

[Tranona]

Agree with VicS First thing to look at is the exhaust run to the transom. It should have a loop or a swan neck well above the waterline to prevent water flowing back into the exhaust pipe. See the schematics in the Vetus catalogue www.vetus.com You can achieve this with either a loop in the exhaust or a Vetus fitting if you are short of space. It performs a different function from the anti syphon valve. You do not need a high rise manifold if you have an AS valve these prevent water syphon back from the cooling system, not through the maain exhaust run - which seems your problem.

 

[jonathanhsm]

loop

I have a big loop up to deck level and down again to trap and assumed this would be enough. But boat has recently been out in force 10 gusts with waves up the jacksie - so assume swan neck was overwhelmed!

 

[jonathanhsm]

exhaust flap

OK after all this it looks like I need a 3 inch "exhaust flap" - (I'll have to measure it exactly) All the ones on the internet seem to be in the USA. Anyone know of a UK supplier?

 

[Tranona]

Not sure a flap is the solution - they are designed for power boats with straight exhausts. There is something else wrong - first place to look is the antisyphon valve as this could be stuck. If you have a swan neck and a water trap you should not get any water blown back through the exhaust. Think about it - it will mean that the stern of the boat is being submerged above the level of the top of the swan neck. Very unlikely.

 

[VicS]

Not sure a flap is the solution - they are designed for power boats with straight exhausts. There is something else wrong - first place to look is the antisyphon valve as this could be stuck. If you have a swan neck and a water trap you should not get any water blown back through the exhaust. Think about it - it will mean that the stern of the boat is being submerged above the level of the top of the swan neck. Very unlikely.

He said, "There is a working anti-siphon valve in place over the raw water inlet so water is not coming from there - in any case I always close the inlet seacock."

I think Id would double check that. Ensure that the anti-syphon valve is located high enough ( Vetus recommend 40cm min above the WL) and really working .. Also ensure that the seacock is shutting off.

Otherwise closing the exhaust outlet seems to be the only solution.


If you and I had not frightened away Rossynant bewteen us perhaps he would have the answer

 

[TopDonkey]

surely with the exhaust pointing straight down at the back on his yacht, the hydraulic force generated as many tonnes of yacht slam down hard onto the waters surface is where the problem is and a swan neck isnt going to cope with such a huge amount and force of water coming at it ?

The answer really is to have the exhaust pointing out the back rather than pointing down at the water ?, but as you cant really change the exhaust outlet location easily, the flap is the easiest solution ?

 

[Tranona]

If you and I had not frightened away Rossynant bewteen us perhaps he would have the answer

Yes, but it would have been even more wordy than my contributions!

 

[fisherman]

It is possible to have a hinged flap over the outlet, fitted with a counterweight which is raised as the flap opens, closes it when not in use. (Counterweight = piece of studding or a bolt through the flap, with a weight on the end). Simpler might be a hose tail on the outlet with a bit of soft hose jubilee clipped over it. That is, if the problem is definitely coming in from that end.

 

[john_morris_uk]

I have had exactly the same problem with our boat. In rough seas water appeared to be forced up the exhaust overwhelming the water trap and eventually finding its way into the engine and hyrdaulic locking it when we went to start the thing.

First partial cure for us was putting a Volvo high rise exhaust on the engine itself. This cured the problem 80% of the time, but we occasionally still had difficulties.

I then discovered that the main run of exhaust from the water trap was in a different (larger) size to the one that came from the engine. This meant that the engine exhaust was not pushing water out from this pipe with as much vim as it ought to and the water trap was ending up very full every time we stopped the engine - a long run of large exhaust partically full of water was too much for thre trap.

I changed the exhaust pipe to the correct size and made sure that there was a decent loop above the waterline and also added a seacock for 'in extremis' conditions. The result has been a quieter engine. No loss in power, and so far no repeats of the problem.

It might also be worth checking that the internal baffles in the water trap haven't melted as some stage, but the engine being run with a blockage of the sea water cooling etc.

 

[jonathanhsm]

Belt and braces

Many thanks all - I think the ultimate solution is to fit an exhaust riser with water injection point low down- there is plenty of room for it above the exhaust elbow - but where do I get one?

I will also try and find exhaust flap and make counterweight in a spirit of belt and braces. Again anyone know where I get three inch exhaust flap?

Failing that I'll put a ball valve in the exhaust line

I think I have managed to attach pic of boat out of water with exhaust outlet on far left of image - where you can see it would be easy for water to be "pumped" up by surging waves

 

[conor54]

Hi,

I had a similar exhaust problem - resulting in an expensive rebuild. I got a local engineering firm to make a high rise exhaust. I also fitted a larger water lock. No trouble since. See some pictures here:

Regards,

Conor

 

[jonathanhsm]

DIY riser

Thanks for that - what does something like that cost? and does it have the requisite swirl chamber etc And what happens when it finally rots/blocks up - I guess you have to commission another.
Don't the manufacturers - ie Perkins or Volvo - make a riser?

 

[john_morris_uk]

Thanks for that - what does something like that cost? and does it have the requisite swirl chamber etc And what happens when it finally rots/blocks up - I guess you have to commission another.
Don't the manufacturers - ie Perkins or Volvo - make a riser?

Yes they do. Its an optional exhaust and water injection manifold with high rise. They are not cheap - perhaps the thick end of £400?

 

[jonathanhsm]

400 quid

gosh - might look for someone breaking an engine!

 

[Talulah]

But ultimately need an exhaust riser. Does anyone manufacture such things? Engine is Perama 18hp M20 - almost identical to Volvo 2020

I had one made by Halyard.
Still going strong.
http://www.halyard.eu.com/Products/exhaust_risers.html

 

[jonathanhsm]

I had one made by Halyard.
Still going strong.
http://www.halyard.eu.com/Products/exhaust_risers.html

How much ... ish?