Exhaust back-flooding

Not exactly the same as mentioned but supposedly similar problem s
I've heard is, when engines have difficulty starting and long periods on the starter that do not clear the exhaust water output from the exhaust causing flowback into the engine and a hydraulic piston /compression situation - and being salt water too...! Some things are less obvious than those being considered at the time.

ianat182
 
Think on this: if you have a very high goose neck there is a lot of water being pushed over it by the engine, a percentage of the total volume, longer run/higher neck= more water. When you shut down that water drops back towards the engine, and just a bit more might tip the balance.
Take it to the extreme, a ludicrously high gooseneck, say fifteen feet, how much water between engine and highpoint? Also it depends on water flow, pipe dia, highly variable between engines/pumps/systems. Enough to flood the engine? It needs more meticulous calculation. Or a small drain cock just behind the engine, to be left open when needed: won't flood the boat, won't prevent startup.
There are more factors, like a turbo. As you open up the exhaust volume increases dramatically as the turbo cuts in while the water flow only increases in linear fashion with engine revs, so at high speed, more gas than water, low speed more water than gas, just before you shut down.
 
fisherman said:
Think on this: if you have a very high goose neck there is a lot of water being pushed over it by the engine, a percentage of the total volume, longer run/higher neck= more water. When you shut down that water drops back towards the engine, and just a bit more might tip the balance.
Take it to the extreme, a ludicrously high gooseneck, say fifteen feet, how much water between engine and highpoint? Also it depends on water flow, pipe dia, highly variable between engines/pumps/systems. Enough to flood the engine? It needs more meticulous calculation. Or a small drain cock just behind the engine, to be left open when needed: won't flood the boat, won't prevent startup.
There are more factors, like a turbo. As you open up the exhaust volume increases dramatically as the turbo cuts in while the water flow only increases in linear fashion with engine revs, so at high speed, more gas than water, low speed more water than gas, just before you shut down.
Click to expand...
Or more sensibly the water is introduced into the exhaust in a mixing chamber at the highest point.
 
fisherman said:
Think on this: if you have a very high goose neck there is a lot of water being pushed over it by the engine, a percentage of the total volume, longer run/higher neck= more water. When you shut down that water drops back towards the engine, and just a bit more might tip the balance.
Take it to the extreme, a ludicrously high gooseneck, say fifteen feet, how much water between engine and highpoint? Also it depends on water flow, pipe dia, highly variable between engines/pumps/systems. Enough to flood the engine? It needs more meticulous calculation. Or a small drain cock just behind the engine, to be left open when needed: won't flood the boat, won't prevent startup.
There are more factors, like a turbo. As you open up the exhaust volume increases dramatically as the turbo cuts in while the water flow only increases in linear fashion with engine revs, so at high speed, more gas than water, low speed more water than gas, just before you shut down.
Click to expand...
I guess that a small engine running into a big bore exhaust system at low rpm will allow a lot of water to remain in the run from the waterlock to the transom.
So the waterlock can start off with quite a lot in it.
I don't suppose the average yacht owner would ever know how full the water lock is, until it's suddenly a real problem?
Might be interesting to see how much is in there some time!
 
NormanS said:
Or more sensibly the water is introduced into the exhaust in a mixing chamber at the highest point.
Click to expand...
Yes, then you have a dry exhaust from engine to high point. OK if you could keep it short. What are you going to do about the heat? I had a dry exhaust, 135HP, it gets hot enough for combustion if unlucky. I had a big engine room, the choice was to let heat out of the 3m of pipe below, hot engine room, or insulate, and have the crew burn themselves on the stack, which was 2in bigger than the silencer above deck.
 
Wing Mark said:
I guess that a small engine running into a big bore exhaust system at low rpm will allow a lot of water to remain in the run from the waterlock to the transom.
So the waterlock can start off with quite a lot in it.
I don't suppose the average yacht owner would ever know how full the water lock is, until it's suddenly a real problem?
Might be interesting to see how much is in there some time!
Click to expand...
Could you find out by sounding it? Or use a meter. Worth knowing.
 
fisherman said:
Could you find out by sounding it? Or use a meter. Worth knowing.
Click to expand...
I might see how easy it is to remove the engine-waterlock hose and dip the level. Might be awkward as it goes through a bulkhead,
I'm not really seeing my boat as the '3 whole days on port tack ' ocean crossing type.
Like a lot of modern-ish boats I guess, it has the Vetus swan-neck thing, angled back at the angle of the transom, which can't really be ideal?

I think one test might be to give some revs (blowing a lot of water out), then drop to idle and see how long it is before water starts coming out again?
 
fisherman said:
Yes, then you have a dry exhaust from engine to high point. OK if you could keep it short. What are you going to do about the heat? I had a dry exhaust, 135HP, it gets hot enough for combustion if unlucky. I had a big engine room, the choice was to let heat out of the 3m of pipe below, hot engine room, or insulate, and have the crew burn themselves on the stack, which was 2in bigger than the silencer above deck.
Click to expand...
It sounds as if yours was a completely dry exhaust. That's not what I was referring to. It's normal to wrap insulation round the length of dry exhaust up to the mixing chamber, where the cooling water is introduced, and from there on it's usually hose. Even when I had a 60 ft fishing boat with a six cylinder Gardner, there was only about one metre of lagged pipe before the mixing chamber at the deckhead of the engine room.
 
NormanS said:
It sounds as if yours was a completely dry exhaust. That's not what I was referring to. It's normal to wrap insulation round the length of dry exhaust up to the mixing chamber, where the cooling water is introduced, and from there on it's usually hose. Even when I had a 60 ft fishing boat with a six cylinder Gardner, there was only about one metre of lagged pipe before the mixing chamber at the deckhead of the engine room.
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Yes exactly, but most folk have compact engines in compact spaces with little or no height to play with. I always struggled when I had a wet exhaust between the choices for arrangement. Stuck with the WFA regs original and ended up with a flooded engine, but so did several other boats, they all got wave slapped up the bum in a NW gale in Hayle. A flap would have saved it.
 
Neeves said:
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.
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I'm surprised at you dismissing the pragmatic; a flap valve would have protected and preserved your engine and would protect the engine in the case outlined in the OP. A flap cannot be forgotten by accident/in an emergency/by crew unfamiliar with the vessel, unlike a gate or ball valve.
 
elenya said:
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.
Click to expand...

Just the ticket,
 
Vetus makes an exhaust that has an inserted check valve which is not affected by waves slapping "up" the transom.
It costs the princely sum of 69 Euro and is a lot easier to install and a lot less faff than any gate valve or other type of solution.

An exhaust system that cannot evacuate the cooling water or store the remainder is simply poorly constructed or improperly dimensioned. A traditional, heavier hull will quite likely have the cooling water injection point below, or significantly below the waterline. Additionally, in an older style boat the freeboard may be considerably lower and hence the swan neck lower than on a modern craft. Properly laid out, the risk to water damage is minimal, regardless of sea conditions. I sailed such a craft (built in 1960) across the Pacific and back, 1500 miles on a single tack and two severe storms. We were pooped numerous times, so that we were up to our necks in water sitting in the cockpit, i.e. the deck was some 3' under water. Never the slightest problem with water ingress through the exhaust though. The fact that the boat, which has done numerous ocean crossings, is, to this day, still sailing with it's original engine should be proof enough that an exhaust system, properly conceived, will keep the engine dry.

Perhaps the Vetus "one size fits all" approach (I know they come in various sizes) does not accommodate all installations, engine sizes or length of exhaust runs.
 
It's clear that some deeply-experienced folk, from their experience, don't see this as a problem. Others with rather different deep-sea experience do see this as a possible issue.

Perhaps it's enough for us to raise this question here, and for those of us who care to consider the expressed views and to consider their options. Isn't that what we're about...?

The fact that the deeply-experienced individual I mentioned in my OP was sufficiently concerned to have that as an item on his 'to do' list was sufficient for me to raise it here for discussion.
 
penfold said:
I'm surprised at you dismissing the pragmatic; a flap valve would have protected and preserved your engine and would protect the engine in the case outlined in the OP. A flap cannot be forgotten by accident/in an emergency/by crew unfamiliar with the vessel, unlike a gate or ball valve.
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I don't actually dismiss the sprung, or possibly - not sprung, - flap. I'd like to try different flap concepts before committing (I like the idea of a collapsing tube/hose as well).

But to go back 20 years - when we commissioned our cat to be built, we were hull No 10, we had the naive expectation that the builder knew what they were doing and we certainly did not question how the vessels were launched. Technology and equipment has moved on and they launch a completely different way now. But you learn over time (that boat builders do not necessarily know what they are doing - and this refers to custom builders, like ours, or the volume production builders).

But to go back to the flaps.

We believe in belt and braces and overkill - which is why our 3rd reef takes the main down to 25% of its original size, why we carry 4 anchors (all of which could be a primary), have shore lines and short lengths of chain for the shore lines (in case we need to tie round rocks), carry a LR and have 3 GPS etc - if we were crossing an ocean we would install both a flap and a ball valve (once bitten, twice shy). Most people think 4 anchors is completely OTT - but on a 3 month cruise we would use all of them (not, yet, all together) - it merits note the combined weight of all 4 is around 32kgs and our primary 75m rode weighs 65kg - hardly excessive for a 38' cat. I'm sure people would equally think a ball valve and flap are OTT - but we do forget and a flap caters for human nature. I note Daydream has never had water in his fuel entered via the deck filler (and I hope he stays in this happy state) but we are not super human and we try to cater for our inadequacies (see note below).

I'm not sure which flap design would be best - I reserve comment. To cater for following seas it should be hinged aft, but that would impose a huge strain on the hinge when making 16 knots (going forward) - which is why I like the idea of a 'collapsing' pipe.

A story with a bit of colour on water in an engine (and a bit of thread drift) - and no mention of anchors!

Our cat was broken into the night before we were due to leave on our summer cruise. The perpetrators were backpackers, duly caught and sent home (to Europe but they emptied the cat of food and drink, including a bottle of single malt, (and the bolt croppers etc etc). This delayed our departure, we had the police on board, finger prints taken etc and we had to re-stock. 10 weeks or so later we were on the first leg of our passage home - the first leg was 120nm. The day we left to head home had poor visibility (100m), cold water, humid atmosphere and no wind and I decided now was a good time to top the fuel up from the 5 x 20l of diesel we carried. One engine was running and there was long swell that we could hear breaking on the rocks somewhere in the mist. I commenced decanting but keeping a watch for spills and the shore line. As I poured the last 20l into the tank the engine coughed and died. I knew immediately what the problem was - but could not understand the reason or background (water in the fuel). We fill our jerry cans from a 'normal' petrol station, its cheaper and has much less chance of contamination.

The back packers had carefully removed most of the diesel from each jerry can and refilled with water and I had just topped our 200l tank up with about 25l of diesel and 75l of water. When I commenced decanting each jerry can - it was diesel - as my attention was distracted by the noise of the swell on the shore line I was then decanting water.

It took hours to remove all, or most of, the water.

By this time the back packers were back where they came from - possibly laughing as to how clever they were.

We often hear of foreign miscreants being put on the next flight back to their home country. Their misdemeanours are held on Oz records - I have constantly hoped their misdemeanours are also on record in their home country (and are more fervent now in my hopes).

Who would have thought.......

Take care, stay safe

Jonathan
 
They sound suspiciously well prepared backpackers if they were able to carry off 75l of diesel(or they found a willing fence despite not being local) plus all that stuff; more like itinerant thieves. Quite a malicious thing to do with the jerry cans, they were already telegraphing their theft with the missing stores and tools so it cannot be put down as an attempt to conceal the act.
 
Perhaps it's my vintage, but I've never had the luxury of believing I could 'motor' all the way into my intended pontoon berth. Time and again, on OPB's boats. it was an expensive tow or a potentially-expensive 'sail in'.

Nae bovver....!
 
penfold said:
They sound suspiciously well prepared backpackers if they were able to carry off 75l of diesel(or they found a willing fence despite not being local) plus all that stuff; more like itinerant thieves. Quite a malicious thing to do with the jerry cans, they were already telegraphing their theft with the missing stores and tools so it cannot be put down as an attempt to conceal the act.
Click to expand...

Its a long sorry story.

They had a acquired a small diesel powered yacht (hence the need for diesel). which they were living on. It turned out they were observant and generally broke into yachts that were infrequently used - and many of the thefts went un-detected for some time. We were picked on as they had seen us stocking up the boat. After breaking into our yacht they decided that maybe they should move their hunting ground and they went north, only about 40nm. They chose their next meal ticket in a large salt water lake, or lagoon, that was entered under a road bridge that was opened on request. They were unaware that the police were already suspicious and when they 'disappeared' the police put out an alert for their yacht. Opening of the bridge required the requesting yacht to declare its name, being in a lagoon with no exit other than the bridge they were soon caught, with their ill gotten gains.

They had drunk the single malt by the time the police caught up with them.



zoidberg said:
It's clear that some deeply-experienced folk, from their experience, don't see this as a problem. Others with rather different deep-sea experience do see this as a possible issue.

Perhaps it's enough for us to raise this question here, and for those of us who care to consider the expressed views and to consider their options. Isn't that what we're about...?

The fact that the deeply-experienced individual I mentioned in my OP was sufficiently concerned to have that as an item on his 'to do' list was sufficient for me to raise it here for discussion.
Click to expand...


We all have different yachts, sail in different areas and have an amazing cross section of experiences. Sailing across an ocean exposes you to many aspects of sailing - but does not necessarily expose you to much anchoring - apparently long term cruisers don't anchor much in the middle of the Atlantic, maybe their rode length is insufficient? Liveaboards may not have much experience at crossing oceans - and I assume you actually don't need to develop sail trimming skills if you are a live aboard. We all have much to learn, much to share and we all need to accept - its unusual if there is only one 'right' answer.

Keep up offering new threads - we don't know what we don't know - until provoked (in the nicest possible way :) ).

Jonathan

Jonathan
 
I cannot imagine what your "backpackers" hoped to achieve by topping up your diesel containers with water. At least they just took the bottle of whisky, and didn't drink most of it and then top it up with p***. ?
 
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