Exhaust back-flooding

[zoidberg]

Listening today to a very experienced ocean single-hander, he tells me of his concerns for possible back-flooding in conditions when heavy seas are crashing into the transom repeatedly - despite his having a Vetus gooseneck bottle properly fitted - with possible seawater back-flooding of the engine through the exhaust system.

He's considering a gatevalve he can screw shut just inboard of his transom exhaust outlet, in appropriate conditions offshore, when he has deployed a Jordan Series Drogue.

What does the hive mind think?

 

[Tradewinds]

Listening today to a very experienced ocean single-hander, he tells me of his concerns for possible back-flooding in conditions when heavy seas are crashing into the transom repeatedly - despite his having a Vetus gooseneck bottle properly fitted - with possible seawater back-flooding of the engine through the exhaust system.

He's considering a gatevalve he can screw shut just inboard of his transom exhaust outlet, in appropriate conditions offshore, when he has deployed a Jordan Series Drogue.

What does the hive mind think?

Well, my Nic39 has it's exhaust outlet amidships, just above the waterline when level, and it has a gate valve on it (shudder) so the people at C&N must have had similar thoughts.

So a valid point - but don't use a gate valve.

PS Don't forget to open it when you want to use the engine - it can be a right bugger to start otherwise.

 

[penfold]

Why not just have a lightly sprung flap valve with a rubber seal? Halyard used to sell these, although a competent fabricator shouldn't have difficulty knocking one up.

 

[Neeves]

Our cat is supplied with 2 x Volvo 2020s. The installation diagram was approved by Volvo. Volvo commissioned the engines. Volvo were on board during a test run, with the engines. During the test run the Volvo commissioning engineer detected an issue and suggested it be checked at the first service, after (from memory) 50 hours - as it might have rectified itself by then (?).

We followed the instructions and the Volvo service engineer at the 50 hour service said there was an issue but again it might rectify itself so at the next service, another 50 hours, if the problem was still there the engine might need to be removed - not much room in our engine bays.

The engine was removed, now at 100 hours. There was a bent con rod. Volvo denied any responsibility but confirmed the only way the con rod could be bent was if water had entered via the (approved) exhaust system. The blame was focussed at us - despite the fact we had insufficient knowledge to even detect the engine noise that raised the concerns.

The arguments over responsibility did not last long - we were absolved of any blame.

Even fully approved systems are not fool proof.

In our case the cat was launched down quite a steep ramp and it maybe that the exhaust plumbing was good, but did not anticipate the transoms being submerged to quite a depth.

If you want certainty you need to have a positive closure system (and I don't think a flap on a spring is fool proof). It would be easy to have a cover over the ignition button saying ....., it would be easy to include a power cut of with a warning cover etc etc.

Water in the fuel is another issue - are you sure the fuel intake located on the deck? is storm proof - it might be good for pottering around the Solent (or Hong Kong) - is it good when having water thrown at it for days on end - been there done that (towed through the protecting reef at San Fernando (Phillinpines) courtesy of the big Nic Navy entry - sister vessel to Kukri (whom were just behind us).

You really need some means to guarantee water is not in the wrong place and be able to detect if the fuel is contaminated etc etc - without the need to run the engine to find out.

If you need the engine to top up batteries regularly then the problems might diminish - if you sail for weeks (or only a few days) without using the engine - lots might happen and you don't really want to find out - when the engine really matters.

Take care, stay safe.

Jonathan

 

[Laminar Flow]

Any exhaust should have a goose neck that reaches up to the deck head.
For 99.9% of all situations that should be quite sufficient.

I have seen installations with an in-line ball or gate valve, however this can be difficult to access as the correct location would be at the exhaust trough-hull. It is also another thing not to forget when starting the engine. Not likely? Well, how many instances do you know of someone forgetting to turn on the raw water cooling valve? I can count at the very least half a dozen, some of which led to catastrophic engine failure.

Vetus offers a couple of models of exhaust with a built-in check valve. I think this type of exhaust with a properly installed goose neck would be perfectly sufficient.

Though I have been through a few storms at sea in a variety of boats and where we were regularly pooped or the boat was continuously awash at times, we never had any issues with taking on water or flooding the engine through the exhaust. None of the boats had neither a check valve nor a shutoff.

I've never taken on water through a closed deck filler.

 

[Blueboatman]

A manual drain on the bottom of the water trap , check daily /weekly/after survival at sea type storm ?
Better, a cork on a string @ exhaust outlet

 

[elenya]

We have a standard ball valve in the exhaust as it exits the hull. We use this on longer passages. We have a tag that we place on the engine start to remind us it is closed.
We do have a goose neck to deck level and a water trap drain but for the cost of a ball valve.
Peace of mind for some people is worth a few dollars. We will never know if we really needed it but hey.

 

[NormanS]

Many years ago, I built a wooden Folkboat. (Great little boat in which we enjoyed some classic cruises). Her auxiliary power was a hand started single cylinder Volvo diesel. We had no electrics at all. The water injection into the exhaust was as high as possible up under the side deck, but these boats sail over on their sides......
I fitted a valve (yes, it was a gate valve) on the exhaust skin fitting on the inside of the transom. My aid memoir was simply always to hang the starting handle on the valve. It worked. I'm sure that nowadays some interlock system could prevent the engine from being started until the valve was proved open.

 

[fisherman]

Seen this happen in harbour when there was a bit of a breeze. If possible, as above, an external flap. I made one, a simple one hinged at the top, with a piece of studding through it, which had two nuts with a lead barrel weight between. The nuts/weight could be adjusted to give more or less closing force, the only thing extra would have been a rubber disc to help the seal. Even a downward looking exhaust can be closed off with the right leverage.
Also seen one with an external tube extension, with a soft hose clamped on, just folds flat when hit by water, flat fire hose ideal.

 

[Wing Mark]

I know of a couple of yachts losing engines to water up the exhaust.
Sailing for several days in following seas, ISTM that the odd wave will slap the transom hard enough t o overcome the swan-neck. Over time this builds up and fill the exhaust.
Perhaps if the swan neck wasn't there, the water might have just run out again?

Obviously, it's not common, most yachts never have an issue.
But maybe it's a good idea to run the engine every day to blow any water out before it accumulates on a long passage?
Some mobo's have little flaps over the exhaust outlet, like on American lorries.

 

[sarabande]

I know of a couple of yachts losing engines to water up the exhaust.

Can you give a citation (reference) ? How did they lose their engines ?


Sailing for several days in following seas, ISTM that the odd wave will slap the transom hard enough t o overcome the swan-neck. Over time this builds up and fill the exhaust.


Perhaps if the swan neck wasn't there, the water might have just run out again?

I am pretty certain you do not have experience of how a swan neck is constructed, and the risk that the OP has identified and for which he is seeking mitigation.


Obviously, it's not common, most yachts never have an issue.

Wild surmise. What do you mean by "most" ? Is that based on your experience ?


But maybe it's a good idea to run the engine every day to blow any water out before it accumulates on a long passage?

And if the water fills the exhaust system before your daily run ? What then ?

Some mobo's have little flaps over the exhaust outlet, like on American lorries.

Flaps are hinged at the top. And if a wave slaps the transom below the flap, it is likely to force the flap upwards.

 

[Moodysailor]

An anecdote from the other side - a marine engineer.

I've replaced more engines that have had water ingress from being lifted incorrectly (stern too high) in the boatyard than I have from water ingress from a following sea. I've also replaced more from blocked exhausts (rags, valves, buckets, hose collapse) than from a following sea.

My view as a sailor is that if I am ever in the situation where I am preparing to deploy a drogue, I don't think I want to be worrying about a gate valve at the exhaust outlet. From an engineering and sailing perspective this just sounds like a solution looking for a problem where one already exists - a properly designed and installed exhaust system, with a suitable rise above the transom and waterlock adequately sized near the engine is not rocket science and is common ground for any engineer worth their salt.

If you happen to be in seas that are so great that water can force itself past that lot, then come and look me up as I'll buy all the beers whilst you tell me that story - it will be epic.. ?

 

[bikedaft]

our engine should have a high rising water mixing elbow, but no room (fitted about 10 years before we got her). we have had water in the engine twice, at the mooring, after a gale (each time). exhaust swan neck is at deck level - but wave tops were also at this level. now i drain exhaust (garden hose from Vetus trap to easily accessed bilge area, with a small ball valve on end of hose) and have fitted a ball valve near transom. never had an issue again.

apart from starting it with gate valve shut... cured by attaching engine key to valve handle...

 

[Moodysailor]

our engine should have a high rising water mixing elbow, but no room (fitted about 10 years before we got her). we have had water in the engine twice, at the mooring, after a gale (each time). exhaust swan neck is at deck level - but wave tops were also at this level. now i drain exhaust (garden hose from Vetus trap to easily accessed bilge area, with a small ball valve on end of hose) and have fitted a ball valve near transom. never had an issue again.

apart from starting it with gate valve shut... cured by attaching engine key to valve handle...

Do you have a waterlock as well as a swan neck?

 

[Moodysailor]

If I had the space on an installation, I would definitely install a water separator in the exhaust line. These were primarily designed to reduce the exhaust splashing noise for equipment such generators, but removing the water part of the equation provides some peace of mind.

 

[bikedaft]

Do you have a waterlock as well as a swan neck?

Yes, one, Vetus. Surveyor suggested add another in line - but that wouldn't cure the problem, just delay water getting to engine.

 

[DownWest]

A Swan had problems with this. One engine was rebuilt, then replaced. I was asked to look at it and reckoned the Volvo water trap was not big enough or low enough after the manifold. Space was a problem for any off the shelf Vetus ones, so made a one off in GRP that was three times the capacity of the Volvo and 300mm lower. Apart from the long length from the trap to the transom, I suspect bumping into head seas might have been a cause.

If fitting a gate valve, maybe keep the engine keys clipped to it? Pref a ball valve, easy to see if open or closed.

 

[Moodysailor]

Yes, one, Vetus. Surveyor suggested add another in line - but that wouldn't cure the problem, just delay water getting to engine.

Thanks. If you have a low deck height then this will be a challenge. The additional waterlock would at least provide some additional security. Some other ideas could be to re-locate the exhaust outlet to a different place (out the way of direct water impact), or using an outlet with non-return flap on it (as referenced in some earlier posts).

 

[webcraft]

Avy-J had a seized gate valve (seized open) just before the exhaust outlet when we got her. No Swan neck, just a loop up to cockpit seat height, and a small waterlock.

I asked the yard to replace the seacock with a gate valve. They charged me handsomely and installed it so the handle was almost inaccessible.

The engine subsequently died, due to historic and possibly current water ingress. We had big following seas a couple of times coming down the Iberian coast, but removing everything from the lazarette to try to access the seacock was out of the question, and by the second time this happened the engine was already dead.

New engine has a high rise exhaust elbow and an adequately sized waterlock. A Swan neck is installed in the cockpit coming, well above deck level.

If you think you need a seacock on your exhaust then you probably need to rethink the whole system. If you must have one, I believe a gate valve is preferable as it is less likely to be affected by heat.

- W

 

[Wing Mark]

An anecdote from the other side - a marine engineer.

I've replaced more engines that have had water ingress from being lifted incorrectly (stern too high) in the boatyard than I have from water ingress from a following sea. I've also replaced more from blocked exhausts (rags, valves, buckets, hose collapse) than from a following sea.

My view as a sailor is that if I am ever in the situation where I am preparing to deploy a drogue, I don't think I want to be worrying about a gate valve at the exhaust outlet. From an engineering and sailing perspective this just sounds like a solution looking for a problem where one already exists - a properly designed and installed exhaust system, with a suitable rise above the transom and waterlock adequately sized near the engine is not rocket science and is common ground for any engineer worth their salt.

If you happen to be in seas that are so great that water can force itself past that lot, then come and look me up as I'll buy all the beers whilst you tell me that story - it will be epic.. ?

I recall the stories not being all that 'epic' just 'and then we reached on port tack for 3 days....' kind of thing.