Exhaust back-flooding

fisherman said:
My contention is that it makes no difference how big the muffler, how long the pipe, it will still contain the same % mix of water and gas, so the system will contain x% water. BUT, it seems very likely that most systems are well over spec in terms of holding water, otherwise there would be more incidents and we would be relating many more experiences of flooded engines.
Both wet exhausts I had were just a swan neck with water injection bend, and a 3m or so hose, in a gentle catenary down and up to the outlet, which was not much lower than the swan neck. I remember being aware of a possible problem when my crew shut the engine down when were loaded and I yelled at him to start it again quick, and no problem. That boat is still fishing and I have spoken to successive owners who have had no trouble. The other one had the slap up flooding, but so did other boats the same night. Its outlet was very high off the water at rest, but the boat sat head down. A flap would have saved it, £8k.
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I agree with you, except for the last part. There is a high likelihood that that vessel would have had problems anyway, flap or not. It was an expensive lesson....
 
fisherman said:
And you don't think there might be other measures in a self righting boat?
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There are - quite a few.

jamie N said:
I'm sure that there are, but I can only say about the obvious ones blocking the exhaust from back-flooding.
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This is correct. The flap is there primarily to prevent water being pushed up the exhaust.

Lifeboats are extremely well designed and engineered (as I'm sure is obvious). They have to cope with roll-over and being towed stern first up ramps. But these are tools designed for specific and extreme tasks - in the same way we wouldn't look at an ambulance or fire engine and take that as the best way to build our cars, it is almost definitely not necessary to copy the engineering of a lifeboat aboard most pleasure craft.

I've cautioned a few times on this thread about not over-engineering and that stands true - most exhaust systems are well designed, and suitable for the task at hand. Those that are not should be looked at and re-engineered when possible. For those who are retrofitting storm equipment, there may be a requirement to prevent water ingress via the transom fitting. And then there are the outliers - the unique cases where due a particular set of events, an owner has been unlucky. I've seen plenty of those through the years, and the owners were grateful for insurance.

As I said in one of my first posts, I've seen more damage from bad winterisation and boats being lifted incorrectly than I have from damage at sea. I'd be more worried in my boatyard than I would sailing around this island....
 
fisherman said:
Yes, but it took twenty years to happen. A bad design that clung on until circs got the better of it.
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Not common, but happens more often than you might think - a marginal design is OK until something else changes. Boat loaded differently, change in location, etc, etc. Then the problem rears it's head...
 
Moodysailor said:
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As I said in one of my first posts, I've seen more damage from bad winterisation and boats being lifted incorrectly than I have from damage at sea. I'd be more worried in my boatyard than I would sailing around this island....
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This thread has certainly raised my awareness about how a boat's exhaust might be vulnerable in less obvious ways.
 
As a coincidence, earlier today for an unrelated reason, I was looking into the engine bay of a chum's boat where the water block was (I believe) upside down. The water block has 2 pipes at it, the exhaust into it, and the exhaust out of it, through a hose and out of the back of the boat. The pipe to the back of the boat was at the top, with the pipe into the water block from the engine, at the bottom.
Is that the right way or the wrong way?
A beer rests on this, so it's important.
 
As I understand it - and a competent marine engineer will politely shoot me down if wrong/misinformed - the Inlet is on the 'high' side, and the 'Outlet' starts 'low down'.

51687360010_9021255b6a_z.jpg


On most Vetus waterlocks, both 'IN' and 'OUT' are moulded into the side of case..... if such is visible.
 
Moodysailor said:
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.. ?
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I recently lost a fully serviceable Volvo 2030 to water ingress whilst out of the water for an annual engine service and powerhose. This boat, a Westerly, has a wet exhaust. The engineers suggested the fault could lie in incorrect lifting, but how could this possibly pitch the boat more than when it tumbles over a wave or wash from a ship?

Could excessively forceful power-hosing drive water into the engine?

Surely a wet exhaust is always more vulnerable than occasional waves crashing into a transom exhaust, but with no problems for 20 years it is obviously a system that works.
 
jamie N said:
As a coincidence, earlier today for an unrelated reason, I was looking into the engine bay of a chum's boat where the water block was (I believe) upside down. The water block has 2 pipes at it, the exhaust into it, and the exhaust out of it, through a hose and out of the back of the boat. The pipe to the back of the boat was at the top, with the pipe into the water block from the engine, at the bottom.
Is that the right way or the wrong way?
A beer rests on this, so it's important.
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jamie N said:
I think that I owe him a beer....
View attachment 125942
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The outlet & inlet are marked as they can be deceiving - as the two images show. What is important is how the WL is routed internally as this provides the 'lock'.

Very sorry, but I think you might need to crack open the wallet. I'd always suggest finding something else and going double or quits though - beer bets are the best kind :cool: ;) (y)
 
chrisD said:
I recently lost a fully serviceable Volvo 2030 to water ingress whilst out of the water for an annual engine service and powerhose. This boat, a Westerly, has a wet exhaust. The engineers suggested the fault could lie in incorrect lifting, but how could this possibly pitch the boat more than when it tumbles over a wave or wash from a ship?

Could excessively forceful power-hosing drive water into the engine?

Surely a wet exhaust is always more vulnerable than occasional waves crashing into a transom exhaust, but with no problems for 20 years it is obviously a system that works.
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This scenario is exactly the one I described, and one I have seen a few time unfortunately. If the vessel is lifted with the stern too high, it is my belief that the quite jerky motion of the vessel in the slings can force water forwards in the engine. Unfortunately in these cases, the smoking gun is evident to see as we know there is engine damage, and we know it is from water ingress - all that is left is for us to work out the sequence of events.

My strongest advice is to drain the waterlock prior to having the boat lifted as this is the best prevention method. Most have a drain for this reason, if the one fitted doesn't have a drain then disconnecting the exhaust hose from the exhaust elbow and moving it clear will do the same job.

And I know this is not possible in some yards, but if possible cranking or firing the engine ashore after lifting - even if only briefly - will push anything in the exhaust out. Do not do this if you believe, or know you have water in the engine though.

A few owners over the years have suggested the cause was high pressure washing (and I even know one who was successful in a claim for this), but my opinion is that this is not the cause - when the hull is being pressure washed, they generally keep the hose moving and do not focus the jet around areas such as the exhaust. There would need to be direct, sustained injection of water directly up the exhaust pipe for this to be the cause, and I can't remember the last time I saw someone in a yard being that incompetent with the pressure washer. I also hold the view that taking this view that prevention is better than claim, so draining the waterlock is the best course of action.
 
Moody sailor,

thanks for such a comprehensive and clear response, I appreciate your time.

hopefully a quick question: would turning off the raw water inlet say a minute before stopping the engine also clear the exhaust? Or would you say this is a high risk strategy?
 
Dad's boat has a Sabb with the option to "dry" the exhaust - a T junction in the cooling water after the engine before it goes into the exhaust - it can be put over the side for 5-10mins prior to sailing in rough seas etc.

Sorry, not sure why i only remembered this now(!)
 
chrisD said:
Moody sailor,

thanks for such a comprehensive and clear response, I appreciate your time.

hopefully a quick question: would turning off the raw water inlet say a minute before stopping the engine also clear the exhaust? Or would you say this is a high risk strategy?
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If you're going to go below and turn off the inlet, might you just as well open a muffler (low point) drain, after shutdown? That won't cause too much grief if it gets forgotten, for not too long anyway.
 
chrisD said:
Moody sailor,

thanks for such a comprehensive and clear response, I appreciate your time.

hopefully a quick question: would turning off the raw water inlet say a minute before stopping the engine also clear the exhaust? Or would you say this is a high risk strategy?
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A bad idea as the rubber hose will begin to overheat very quickly once the water stops, even a minute could cause damage and cumulatively over a season likely delaminate and block the exhaust.
 
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