Following seas flooding engines

[nofacey]

I’ve experienced a couple boats with properly designed/installed wet exhaust systems back flood in prolonged heavy seas from astern.

Install full bore valves in the exhaust run - leave them open while coastal cruising, shut them as engine turned off offshore, hang keys on “valve closed” hook. Did same with genset.
1) motor won’t start with exhaust closed (& it doesn’t blow up either)
2) you become very accustomed to “open valve, start engine”

[Uplander]

A simple answer is to clamp a section of a motorcycle tube to the exhaust. Collapses when a following sea hits it yet allows the exhaust to exit.

[NYSail]

Originally Posted by yachtski

L40 when sailing with following seas and wind 120 to 180 especially on the starboard side have found water is coming up the exhaust .. some people are trying to tell me that is from the cooling water not having a siphon loop. That small amount of water from the heat exchanger tubes that might possibly trickle in the muffler is nothing compared to what can be stuffed up that exhaust by a hard following seas.. there's some other posts and threads in other sections people experiencing this. Considering exhaust flaps but facing the wrong way they become a scoop. Is the wave coming up from the bottom as the boat goes down from the back from a wave breaking on quarter ?? There is also some good illustrations on good exhaust design like the North Sea system that has a poor on both sides and the water can flow through while the exhaust has to come down from the top into that passage. I'll be the best but not the easiest solution. Some experts talk about putting a valve to close the exhaust outlet.. in the meantime I know when I'm sailing in that position I'm running that engine. ...

Centek makes a check valve for the exhaust system…… or you can add a gooseneck to prevent water backflow.

Greg
s/v Souleil

[Looking4Neptune]

I have a 2010 Leopard 46 and have had saltwater flood back up the exhaust twice in the past six weeks. Had to pull the injectors, suction the water out. The second time the exhaust system was so flooded that every time I suctioned and hand cranked, water flooded in again. I had to disassemble the exhaust system to dump the water.

I just put foam plugs in the exhaust pipes and cards hanging over the start switch to remove the plugs before starting. There is very little that can be done to raise the exhaust hose routing with the layout of the engine bay.

Sure hope it works. There are no diesel mechanics out here in the outer Cook Islands.

On the bright side, I met a great diesel mechanic in Raiatea who built a tool for me to remove stuck fuel injectors and taught me the process. I was able to do it myself in Aitutaki. If you need a great mechanic in Raiatea, ask for Hio at Raiatea Carenage.

[skipperpete]

Originally Posted by Looking4Neptune

I have a 2010 Leopard 46 and have had saltwater flood back up the exhaust twice in the past six weeks. Had to pull the injectors, suction the water out. The second time the exhaust system was so flooded that every time I suctioned and hand cranked, water flooded in again. I had to disassemble the exhaust system to dump the water.

I just put foam plugs in the exhaust pipes and cards hanging over the start switch to remove the plugs before starting. There is very little that can be done to raise the exhaust hose routing with the layout of the engine bay.

Sure hope it works. There are no diesel mechanics out here in the outer Cook Islands.

On the bright side, I met a great diesel mechanic in Raiatea who built a tool for me to remove stuck fuel injectors and taught me the process. I was able to do it myself in Aitutaki. If you need a great mechanic in Raiatea, ask for Hio at Raiatea Carenage.

I’m curious to know if it was the same engine both times and under the same wind and sea conditions.
I’ve never seen a valve of any type that remained operable in an exhaust hose, and the physical size of 75 mm full flow ball valve is a difficult thing to accommodate , it needs a locker of its own if regular visits are planned, maybe big plastic ball valve might work. Nearly all the engines I’ve encountered that were terminally damaged by wet exhausts DID NOT get flooded by following seas but by far more predictable circumstances and the only engine I know for sure that was flooded UP the exhaust happened while the vessel was aground. She either flooded on the falling tide or after she dried out and the flood tide reached over the side deck as she refloated.
The damage caused by an engine flooding often doesn’t become apparent until long after the initial event, if the water gets into the sump, even if an oil change is done immediately there’s inevitably a small amount of seawater below the suction pickup that gets circulated through the lube oil circuit and often ends up in the injector pump housing ( inline and cassette pumps mainly, DPA and VE are fuel lubricated) and 6 months later, maybe a year, the engine won’t start and corrosion is found in the injector pump.

[Looking4Neptune]

Skipper Pete - it was the stbd engine both times. Its exhaust hose is at least 3 feet shorter than the port engine. I just finished another passage with 3+ meter seas hitting us on the aft quarter and the foam plug I made got stuffed into the exhaust and it appears that it is flooded again. I will know in an hour or so. Very disappointing.

[KevinE]

This issue was discussed on on one of the leopard FB groups I follow where there was no anti siphon loop. I guess leopard said this is the responsibility of the engine supplier and the engine supplier said it was the responsibility of the builder. OMFG.

What is typical normal practice WRT to engine commissioning on a new build? Is this done by the engine supplier or the builder? From a cost perspective I think I know the answer...

[mvweebles]

Originally Posted by KevinE

This issue was discussed on on one of the leopard FB groups I follow where there was no anti siphon loop. I guess leopard said this is the responsibility of the engine supplier and the engine supplier said it was the responsibility of the builder. OMFG.

What is typical normal practice WRT to engine commissioning on a new build? Is this done by the engine supplier or the builder? From a cost perspective I think I know the answer...

Responsibility of the installer based on installation parameters. Above, I posted a picture from Northern Lights showing three different install options depending on configuration of engine vs waterline. There is no way for the engine builder to know this ahead of time unless they were consulted and made a specific recommendation. My guess is the engine documentation provided by the engine OEM spells this out quite clearly

The builder knows this..if they say it's the engine manufacturers responsibility, they are shoveling BS.

[skipperpete]

Originally Posted by Looking4Neptune

Skipper Pete - it was the stbd engine both times. Its exhaust hose is at least 3 feet shorter than the port engine. I just finished another passage with 3+ meter seas hitting us on the aft quarter and the foam plug I made got stuffed into the exhaust and it appears that it is flooded again. I will know in an hour or so. Very disappointing.

Oh bugger, I hope it didnt get water up the pipe to the engine. A friend of mine has a Knysna 44 and I look at his exhaust system with horror, if ever there was a system destined to fail, this is it….. but in over 25 years it never has. The engines are amidship and the exhaust comes out of the mixer and into a small vetus waterlock all the way through the aft cabin and then the shower/toilet …into the steering locker…. Then a loop up to about 600mm above the waterline and down to the overboard exactly ON the waterline. The single hose run is over 20’long and entirely down to the engine from the top of the loop in the steering locker. My biggest concern is actually the stainless steel overboard fitting, one hull is overloaded and that fitting is constantly ½ submerged, the other hull is less loaded and the overboard is exactly on the waterline, if either of these thru hulls fail, flooding is inevitable and even though this system stands out as one most likely to flood from following or quartering seas it never has despite the boat being in fairly foul weather many times in its life.
Oh, it is fitted with vent loops near the mixer but on this boat they were more of a precaution than a necessity, the injection point on the mixer elbows is above the waterline.

[CarlF]

At least on the Leopard 50's the flooded engines I've heard about have been caused by cooling water not waves up the stern. The Yanmar 4JH4's are known to have "leak by" past the impeller. Over days of fast sailing enough water leaks by the impeller to fill the exhaust and overflow into the cylinders.

Starting the engine briefly every 6 hours or so will blow the water out. A better fix is to install a high vented loop in the hose from the raw water pump to the entrance of the heat exchanger. Many have done this.

The problem is not unique to Leopards but can strike most brands of cats using a 4JH4

[Kazamaran]

Ok….lets take a step back for a minute. The exhaust hose loop is a sea water ingress prevention method by restricting water flow into the exhaust system while underway with the engine off. A poorly designed loop and not enough height from the engine exhaust will surely do it (manometer effect). Generally a fairly unique circumstance on catamarans. But heavy following seas continually pressurizing a poor loop will surely be cause for concern. Others have mentioned, starting the engine periodically, exterior flaps etc. Some folks even recommend cracking the exhaust canister drain plug. I say whatever works, but rerouting of the exhaust hose to its highest point would be my first fix. My engines are roughly three feet from the exhaust hull opening to the wet exhaust canister.

The vented loop discussion is different in that the vacuum breaker is mounted in the raw water input line at the top of a hose loop. This prevents any the chance for water entering the system and eventually the engine caused by a siphoning effect that can occur. This can sometimes happen when a boat is simply bouncing around with the raw water inlet valve open.

So in essence the OP discussion has gone in two different directions. Beware, one won’t fix the other.

Cheers, K

[SailingHarmonie]

Originally Posted by skipperpete

I’ve never seen a valve of any type that remained operable in an exhaust hose, and the physical size of 75 mm full flow ball valve is a difficult thing to accommodate , it needs a locker of its own if regular visits are planned, maybe big plastic ball valve might work.

With all due respect, because you personally have not seen a thing does not mean it does not exist, or even is rare. I have not seen a kangaroo. But some people who talk with an odd accent insist they are common animals…

There are highly reliable butterfly valves, for example, in sizes from small, to way bigger than you have ever seen, that would work fine in this service. If you only look in your local chandlery you won’t find them, but they do exist.

It is of course infinitely better to have a properly designed exhaust system that does not require such shenanigans by providing passive protection against seawater intrusion.

A boat designed without the possibility of installing a proper exhaust system in the space allowed, is just a badly designed boat. Period. Blaming the problems on the engine manufacturer is totally bogus. When you see stuff like that you should ask yourself, “What else did the screw up to save money?”

[Cheechako]

On one boat I had the engine flood minimally right at the dock. The quarter was exposed to open water and low wind chop did it. It would slap right into the exhaust opening. The boat had some rise in the exhaust but it seemed to just pump it in. I think the rubber flappers would avoid it on most boats, but they seem harder to find for sailboat smaller outlets and the outlet fittings often dont protrude enough to put one on..

[Looking4Neptune]

It did happen a 3rd time. As mentioned, the plugs I made had gotten stuffed into the exhaust exit pipe and turned sideways so that they wouldn’t prevent water getting by. Now I have put acrylic caps that are bigger than the opening so they won’t be stuffed in again. I hope that is the end of the problem.

CarlF mentioned that the Yamar 4JH4 (my engine) can have water forced up past the impeller. I have to think about that more. It appears to me that there is always a compressed impeller fin between the input and output of the pump that should stop the water. Maybe enough pressure, over enough time will overcome this?

On the upside, I’m getting very good at pulling my injectors and pulling salt water from my engine ��

[dougweibel]

Originally Posted by GordMay

"Inner Tube", effective though it may be, in preventing back flooding, will NOT meet the required 'standards'.

Is this relevant if the inner tube is attached outside the transom? Doesn't seem like it is exactly "exhaust hose" in that situation. I don't know. I'm just asking.