Generator Hydro-Locking

[Alaskan Sea-Duction]

So this has happened to me twice now. Sea Conditions were following Seas or off the Port Stern.

Setup:

Genny in cockpit.
Exhaust line is below waterline then enters lift muffler. Top of lift muffler just below water line.

Genny exhaust designed to empty into Port Engine Exhaust.

See schematic.

Solutions:

1. Flapper on main engine exhaust. Problem exhaust tube is 8.5 inches.
2. Install a check valve on top of lift muffler. Exhaust is 2 inches.
3. Install a loop in the exhaust line. Can genny handle this?

I have no way of knowing if this is the original design. When we bought the boat in 03, the generator had new exhaust lines.

I am heading over to Shearwater Marine and see what they come up with, but as always I put forth this issue to my TF brothers.

What say you?

 

[Ka_sea_ta]

I'm certainly not an expert on marine exhaust system but every boat that I've had with the genny in the lazerette had it's own dedicated exhaust with a anti siphon loop after the lift muffler that was well above the waterline... A flapper would be a belt/suspender thing.... Good luck a inop genny can be a show stopper. A lift muffler should have a internal check valve

 

[DavidM]

That is a POS genny exhaust system and is guaranteed to back flood the genny. Whoever designed and built this should be shot. Any water that sloshes back into the main exhaust will go into the generator's lift muffler, fill it up and back into the genny engine.



Your best solution would be an exhaust loop as high as possible from the lift muffler before it enters the main engine exhaust. The loop needs to be about 12" above the entry point into the main exhaust line. A flapper on the exhaust hose would also help.


I don't much like check valves although Centek makes them. They can fail and stick open.


And finally what have you done after the two hydrolocks? I would change the oil a couple of times at minimum to get the salt water out of it. If these weren't done then look into the oil filler if it lets you see the exhaust train and look for rust spots on the rockers and springs. If so I would lap the valves.



David

 

[O C Diver]

Have never understood why people go to the effort of building a lift muffler into an exhaust system, to only get marginal lift above sea level. My engine lift is over 24" above sea level and the generator which ties into the main engine exhaust tube, has a lift of around 48" above sea level.

Ted

 

[dhays]

Sounds to me like the permanent solution is to redesign the muffler system so you get adequate rise above the WL. In your current situation, you may try an exhaust flap and a check valve to try and avoid the problem on this trip. I think it may be a matter of what you can get done in a timely manner, where you are currently, and at what cost. I would imagine that this time of year, most shops and yards are going to be pretty busy.

 

[kchace]

Northern Lights has a good installation manual that clearly defines how to build a safe exhaust system.


https://www.google.com/url?sa=t&rct...s/IM1000.pdf&usg=AOvVaw0gVNqMpjVHGve4SGFNyArh


Ken

 

[cafesport]

Northern lights also has white paper called “ Don’t drown me “ that is a list of do’s and don’ts for marine exhaust specs.

 

[Greg S]

Flapper on the port, main, solution #1, would make it worse IMHO. Don't think of it as the following sea pushing into the genny but rather the port engine exhaust pushing its cooling water into it because it can't escape out the normal route.

 

[boatpoker]

Genny exhaust designed to empty into Port Engine Exhaust.

Surveyor should have mentioned ABYC ..... 1.5.7 A separate exhaust system and terminus shall be provided for each engine and generator installation.

 

[twistedtree]

Flapper on the port, main, solution #1, would make it worse IMHO. Don't think of it as the following sea pushing into the genny but rather the port engine exhaust pushing its cooling water into it because it can't escape out the normal route.

I suspect this is what's happening. You have residual water in the lift muffler. That's normal. In calm seas, your main exhaust is continually blowing it's pipe clear, so not creating back pressure to the gen exhaust.


Now throw in following seas, and your main exhaust is periodically getting submerged. Pressure builds to blow out the water, but that same pressure also pushes back into the gen lift muffler and pushes that water back towards and into the gen. Like Dave says, it's a crap design.


I think the correct fix is to add a dedicated exhaust thruhull for the gen, and be sure there is enough of a loop in the line. The "Don't Drown Me" paper from NL is a good reference.


A shorter term fix would be to install a shutoff valve between the muffler and the gen, or perhaps between the lift muffler outlet and the main exhaust tube. If you put it between the lift and main exhaust, just make sure there is sufficient drop from the gen to the lift muffler so you don't get slosh back into the gen. Placing the valve between the gen and lift muffler would have the most guaranteed results.


The down side of a valve is that you need to be absolutely sure that you re-open it before trying to run the generator, and you need to remember to close it if conditions are the least unsettled. So it's not a good longer term solution, but probably something you could easily get the parts for and implement with minimal disruption to your trip. Then fix it right over the winter.

 

[Ski in NC]

Can you do an elevation drawing (showing a side view) of the same plumbing?

 

[Alaskan Sea-Duction]

Northern Lights has a good installation manual that clearly defines how to build a safe exhaust system.


https://www.google.com/url?sa=t&rct...s/IM1000.pdf&usg=AOvVaw0gVNqMpjVHGve4SGFNyArh


Ken

Thank you for the reference.

Northern lights also has white paper called “ Don’t drown me “ that is a list of do’s and don’ts for marine exhaust specs.

Thank you

Flapper on the port, main, solution #1, would make it worse IMHO. Don't think of it as the following sea pushing into the genny but rather the port engine exhaust pushing its cooling water into it because it can't escape out the normal route.

It could, but the main exhaust tube is over 8 inches so I don't think it is coming from the main. This condition has only happened in following seas, so with those and the cooling water from the main, it is possible, but not from just the main exhaust.

Surveyor should have mentioned ABYC ..... 1.5.7 A separate exhaust system and terminus shall be provided for each engine and generator installation.

It might be that this was not a requirement in 1988. Besides ABYC only recommends, it can't require anything.

 

[Alaskan Sea-Duction]

So it would appear I do not have a loop after the lift muffler. I will need to get me some exhaust hose when I get to K-Town.

Thanks Ken for the reference. It helped a lot. My system looks just like the one depicted in the manual, except for the loop.

One nice thing about the genny exhaust emptying into the main exhaust is it is supper quiet.

 

[sunchaser]

Shearwater should have the loop hose you need and a young agile guy to connect it.

 

[Northern Spy]

Vetus makes a water lock gooseneck that might help.

I gave away a 2" one that I pulled out of my old main exhaust system a few years back to a transient passing through Powell River who had the exact same problem with his generator.

I have a 3" one for my main engine now.

 

[twistedtree]

The loop will help if the issue is water flooding back from the main exhaust, but I really don't think that's what's happening.


I really think that the same exhaust back pressure that blows the water out of the lift muffler from the genny side, is blowing the water backwards into the genny from the main when the main exhaust goes under water completely from following/quartering seas. The back pressure developed by the main will push equally against the water in the flooded exhaust tube, and against the water in the lift muffler. It will blow the exhaust tube water out the back, and blow the lift muffler water into the generator.

 

[DavidM]

The loop will help if the issue is water flooding back from the main exhaust, but I really don't think that's what's happening.


I really think that the same exhaust back pressure that blows the water out of the lift muffler from the genny side, is blowing the water backwards into the genny from the main when the main exhaust goes under water completely from following/quartering seas. The back pressure developed by the main will push equally against the water in the flooded exhaust tube, and against the water in the lift muffler. It will blow the exhaust tube water out the back, and blow the lift muffler water into the generator.

You may be right but the solution is the same: install a high exhaust loop in the generator exhaust and make it exit the transom separately.


David

 

[Ski in NC]

Yep, never liked exhaust shared between mains and genny. It is done, and some do fine, but get tailpipe submerged or slapped by a wave and the genny (if off) can get a mouthful, more likely than if it had it's own tailpipe. A hump at discharge of water lift is absolutely needed. A foot or two of hump.

I also advise my guys that if you get in rough stuff, just leave genny running. Water won't back up into it running.

 

[Alaskan Sea-Duction]

Thanks everyone for the help. I got a section of hose here at Shearwater, but was only able to raise the hose a couple of inches. According to the NL and my Onan install manual it states the loop needs to be "at lease" 1 foot. I can't get that.

So I ordered one of these and had it shipped to Ketchikan to Frontier Shipping.

https://www.defender.com/product3.jsp?path=-1|311|2349040|2349042&id=1656822

 

[Northern Spy]

Another guide with some reference numbers:

https://www.vetus.com/media/magentominds/sasdocument/20121106234215_0.pdf

 

[Crusty Chief]

Good thing were not on this trip with you, I’d be spending all your money (mostly on Libations) to supervise. LOL

Some great info from the fellow TF’ers, as usual.

Cheers gang

 

[Ski in NC]

Is the overhead too low to get some good rise in the hump?

 

[Greg S]

The loop will help if the issue is water flooding back from the main exhaust, but I really don't think that's what's happening.


I really think that the same exhaust back pressure that blows the water out of the lift muffler from the genny side, is blowing the water backwards into the genny from the main when the main exhaust goes under water completely from following/quartering seas. The back pressure developed by the main will push equally against the water in the flooded exhaust tube, and against the water in the lift muffler. It will blow the exhaust tube water out the back, and blow the lift muffler water into the generator.

This is the point I was describing with my comment.

 

[Northern Spy]

This is the point I was describing with my comment.

Yes. And that is why a gooseneck is preferable to just a plain hose loop. It has a volume chamber that would have to fill prior to back spilling over.

 

[twistedtree]

Yes. And that is why a gooseneck is preferable to just a plain hose loop. It has a volume chamber that would have to fill prior to back spilling over.

Just for clarity, where are you proposing the loop? Between the generator and lift muffler, or between the lift muffler and the main engine exhaust tube?

 

[Northern Spy]

Just for clarity, where are you proposing the loop? Between the generator and lift muffler, or between the lift muffler and the main engine exhaust tube?

In between the lift muffler and the main exhaust. But if he has no room for a hose, he has no room for this. Common in sailboats, with low hp diesels deep in the hull.

Look at the flow arrows on the attached drawing.

It would have the same purpose as the hump a hose after the water lock, but allows for volume on the downhill side which maintains the flow velocity on the gen exhaust, while providing a flood volume from the main engine exhaust.

 

[DDW]

Easiest short term solution is just to keep the genset running in the problematic conditions.

 

[sunchaser]

Easiest short term solution is just to keep the genset running in the problematic conditions.

Any stretch of the next 2000 + miles for ASD can be problematic. He is on the right track, fix it now so his very nice genset doesn't suffer a sad demise and ruin his trip.

 

[Steve DAntonio]

No engine or gen manufacturer warrants water entry into the cylinders, regardless of age because if you follow the installation instructions, there's virtually no way water can get in. To me that's very telling, I see violations of exhaust installation guidelines, for propulsion and genset engines, all too often. In many cases they've been that way for years before water actually makes its way into the cylinders.

This drawing is for Northern Lights, but it's pretty much what all genset manufacturers recommend https://www.northern-lights.com/media/PDFs/misc_pdfs/dont_drown_me.pdf

While you can have them as a belt and suspenders, I don't like to rely on check valves and flappers to keep water out out of engines/gens because they fail too often.

Also, there is an important difference between siphoning and flooding, this articles details the issue for a genset flooding scenario specifically https://www.proptalk.com/siphoning-vs-flooding.

General details of exhaust systems Exhaust system design - Ocean Navigator - May/June 2018

If you want the exhaust 'long story', you can find a detailed article here http://stevedmarineconsulting.com/wp-content/uploads/2014/03/ExhaustSystems170-FINAL.pdf

 

[ben2go]

I was going to post the don't drown me PDF but didn't know how to insert the PDF file into a post. I'm glad someone posted it. Thanks, Steve. That document can also help with main engine issues as well.